
Lipopolysaccharide (LPS), now more commonly known as endotoxin,
is a collective term for components of the outermost membrane of the
cell envelope
The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In Gram-negative bacteria an bacterial outer membrane, outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is abse ...
of gram-negative bacteria, such as ''
E. coli'' and ''
Salmonella
''Salmonella'' is a genus of bacillus (shape), rod-shaped, (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two known species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' ...
''
with a common structural architecture. Lipopolysaccharides are large
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s consisting of three parts: an outer core
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
termed the O-
antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
, an inner core
oligosaccharide
An oligosaccharide (; ) is a carbohydrate, saccharide polymer containing a small number (typically three to ten) of monosaccharides (simple sugars). Oligosaccharides can have many functions including Cell–cell recognition, cell recognition and ce ...
and
Lipid A (from which toxicity is largely derived), all covalently linked. In current terminology, the term endotoxin is often used synonymously with LPS, although there are a few endotoxins (in the original sense of
toxin
A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...
s that are inside the bacterial cell that are released when the cell disintegrates) that are not related to LPS, such as the so-called
delta endotoxin protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s produced by ''
Bacillus thuringiensis''.
Lipopolysaccharides can have substantial impacts on human health, primarily through interactions with the immune system. LPS is a potent activator of the immune system and is a
pyrogen (agent that causes fever).
In severe cases, LPS can trigger a brisk host response and multiple types of acute organ failure
which can lead to
septic shock. In lower levels and over a longer time period, there is evidence LPS may play an important and harmful role in
autoimmunity
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease ...
,
obesity
Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...
,
depression, and
cellular senescence
Cellular senescence is a phenomenon characterized by the cessation of cell division. In their experiments during the early 1960s, Leonard Hayflick and Paul Moorhead found that normal human fetal fibroblasts in culture reach a maximum of appro ...
.
Discovery
The toxic activity of LPS was first discovered and termed ''endotoxin'' by
Richard Friedrich Johannes Pfeiffer. He distinguished between
exotoxins, toxins that are released by bacteria into the surrounding environment, and endotoxins, which are toxins "within" the bacterial cell and released only after destruction of the bacterial outer membrane. Subsequent work showed that release of LPS from
Gram negative
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists of ...
microbes does not necessarily require the destruction of the bacterial cell wall, but rather, LPS is secreted as part of the normal physiological activity of
membrane vesicle trafficking in the form of
bacterial outer membrane vesicles (OMVs), which may also contain other
virulence factor
Virulence factors (preferably known as pathogenicity factors or effectors in botany) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following:
* c ...
s and proteins.
Functions in bacteria
LPS is a major component of the outer cell membrane of
gram-negative bacteria
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...
, contributing greatly to the structural integrity of the bacteria and protecting the membrane from certain kinds of chemical attack. LPS is the most abundant
antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
on the cell surface of most gram-negative bacteria, contributing up to 80% of the outer membrane of ''E. coli'' and ''Salmonella''.
LPS increases the negative charge of the
cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
and helps stabilize the overall membrane structure. It is of crucial importance to many gram-negative bacteria, which die if the genes coding for it are mutated or removed. However, it appears that LPS is nonessential in at least some gram-negative bacteria, such as ''Neisseria meningitidis'', ''Moraxella catarrhalis'', and ''Acinetobacter baumannii''. It has also been implicated in non-pathogenic aspects of bacterial ecology, including surface adhesion,
bacteriophage
A bacteriophage (), also known informally as a phage (), is a virus that infects and replicates within bacteria. The term is derived . Bacteriophages are composed of proteins that Capsid, encapsulate a DNA or RNA genome, and may have structu ...
sensitivity, and interactions with predators such as
amoebae. LPS is also required for the functioning of
omptins, a class of bacterial protease.
Composition

LPS are amphipathic and composed of three parts: the O antigen (or O polysaccharide) which is hydrophilic, the
core oligosaccharide (also hydrophilic), and
Lipid A, the hydrophobic domain.
O-antigen
The repetitive
glycan
The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate ...
polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
contained within an LPS is referred to as the O
antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
, O
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
, or O side-chain of the bacteria. The O antigen is attached to the core oligosaccharide, and comprises the outermost domain of the LPS molecule. The structure and composition of the O chain is highly variable from strain to strain, determining the serological specificity of the parent bacterial strain;
there are over 160 different O antigen structures produced by different ''
E. coli'' strains.
The presence or absence of O chains determines whether the LPS is considered "rough" or "smooth". Full-length O-chains would render the LPS smooth, whereas the absence or reduction of O-chains would make the LPS rough. Bacteria with rough LPS usually have more penetrable cell membranes to hydrophobic antibiotics, since a rough LPS is more
hydrophobic
In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, thu ...
. O antigen is exposed on the very outer surface of the bacterial cell, and, as a consequence, is a target for recognition by host
antibodies
An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...
.
Core
The core domain always contains an oligosaccharide component that attaches directly to
lipid A and commonly contains
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose
Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...
s such as
heptose and
3-Deoxy-D-manno-oct-2-ulosonic acid (also known as KDO, keto-deoxyoctulosonate). The core oligosaccharide is less variable in its structure and composition, a given core structure being common to large groups of bacteria.
The LPS cores of many bacteria also contain non-carbohydrate components, such as phosphate, amino acids, and ethanolamine substituents.
Lipid A
Lipid A is, in normal circumstances, a
phosphorylated glucosamine
Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylated proteins and lipids. Glucosamine is part of the structure of two polysaccharides, chitosan and chitin. Glucosamine is one of the mo ...
disaccharide
A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common examples are sucrose, ...
decorated with multiple
fatty acids
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
. These hydrophobic fatty acid chains anchor the LPS into the bacterial membrane, and the rest of the LPS projects from the cell surface. The lipid A domain is the most bioactive and responsible for much of the toxicity of
Gram-negative bacteria
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...
. When bacterial cells are
lysed by the
immune system
The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
, fragments of membrane containing lipid A may be released into the circulation, causing fever, diarrhea, and possible fatal endotoxic septic shock (a form of
septic shock). The Lipid A moiety is a very conserved component of the LPS.
However Lipid A structure varies among bacterial species. Lipid A structure largely defines the degree and nature of the overall host immune activation.
Lipooligosaccharides
The "rough form" of LPS has a lower molecular weight due to the absence of the O polysaccharide. In its place is a short oligosaccharide: this form is known as Lipooligosaccharide (LOS), and is a glycolipid found in the outer membrane of some types of
Gram-negative bacteria
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...
, such as ''
Neisseria'' spp. and ''
Haemophilus'' spp.
LOS plays a central role in maintaining the integrity and functionality of the outer membrane of the
Gram negative
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists of ...
cell envelope. LOS play an important role in the pathogenesis of certain bacterial infections because they are capable of acting as
immunostimulators and immunomodulators.
Furthermore, LOS molecules are responsible for the ability of some bacterial strains to display molecular
mimicry
In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. In the simples ...
and
antigenic diversity, aiding in the evasion of host immune defenses and thus contributing to the
virulence of these bacterial
strains. In the case of ''
Neisseria meningitidis'', the
lipid A portion of the molecule has a symmetrical structure and the inner core is composed of
3-deoxy-D-manno-2-octulosonic acid (KDO) and
heptose (Hep) moieties. The outer core oligosaccharide chain varies depending on the bacterial
strain.
LPS detoxification
A highly conserved host enzyme called
acyloxyacyl hydrolase (AOAH) may detoxify LPS when it enters, or is produced in, animal tissues. It may also convert LPS in the intestine into an LPS inhibitor. Neutrophils, macrophages and dendritic cells produce this lipase, which inactivates LPS by removing the two secondary acyl chains from lipid A to produce tetraacyl LPS. If mice are given LPS parenterally, those that lack AOAH develop high titers of non-specific antibodies, develop prolonged hepatomegaly, and experience prolonged endotoxin tolerance. LPS inactivation may be required for animals to restore homeostasis after parenteral LPS exposure. Although mice have many other mechanisms for inhibiting LPS signaling, none is able to prevent these changes in animals that lack AOAH.
Dephosphorylation of LPS by
intestinal alkaline phosphatase can reduce the severity of ''
Salmonella tryphimurium'' and ''
Clostridioides difficile''
infection
An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...
restoring normal gut microbiota.
Alkaline phosphatase prevents intestinal inflammation (and
"
leaky gut") from bacteria by dephosphorylating the Lipid A portion of LPS.
Biosynthesis and transport

The entire process of making LPS starts with a molecule called lipid A-Kdo2, which is first created on the surface of the bacterial cell's inner membrane. Then, additional sugars are added to this molecule on the inner membrane before it's moved to the space between the inner and outer membranes (
periplasmic space) with the help of a protein called MsbA. The O-antigen, another part of LPS, is made by special enzyme complexes on the inner membrane. It is then moved to the outer membrane through three different systems: one is Wzy-dependent, another relies on ABC transporters, and the third involves a synthase-dependent process.
Ultimately, LPS is transported to the outer membrane by a membrane-to-membrane bridge of lipolysaccharide transport (Lpt) proteins.
This transporter is a potential antibiotic target.
Biological effects on hosts infected with Gram-negative bacteria
LPS storage in the body
The human body carries endogenous stores of LPS. The epithelial surfaces are colonized by a complex microbial flora (including gram-negative bacteria). Gram-negative bacterial will shed endotoxins. This host-microbial interaction is a symbiotic relationship which plays a critical role in systemic immunologic homeostasis. When this is disrupted, it can lead to disease such as endotoxemia and endotoxic septic shock.
Immune response
LPS acts as the prototypical endotoxin because it binds the
CD14
CD14 ( cluster of differentiation 14) is a human protein made mostly by macrophages as part of the innate immune system. It helps to detect bacteria in the body by binding lipopolysaccharide (LPS), a pathogen-associated molecular pattern (PAMP). ...
/
TLR4/
MD2 receptor
Receptor may refer to:
* Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...
complex in many cell types, but especially in
monocytes
Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also i ...
,
dendritic cells
A dendritic cell (DC) is an antigen-presenting cell (also known as an ''accessory cell'') of the mammalian immune system. A DC's main function is to process antigen material and present it on the cell surface to the T cells of the immune system ...
,
macrophage
Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...
s and
B cell
B cells, also known as B lymphocytes, are a type of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or inserted into the plasm ...
s, which promotes the secretion of pro-
inflammatory cytokine
Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling.
Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...
s,
nitric oxide
Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...
, and
eicosanoids.
Bruce Beutler was awarded a portion of the 2011 Nobel Prize in Physiology or Medicine for his work demonstrating that
TLR4 is the LPS receptor.
As part of the cellular
stress response,
superoxide
In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of t ...
is one of the major
reactive oxygen species
In chemistry and biology, reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from diatomic oxygen (), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (H2O2), superoxide (O2−), hydroxyl ...
induced by LPS in various cell types that express TLR (
toll-like receptor
Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane protein, single-spanning receptor (biochemistry), receptors usually expressed on sentinel cells such as macrophages ...
). LPS is also an exogenous
pyrogen (fever-inducing substance).
LPS function has been under experimental research for several years due to its role in activating many
transcription factor
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...
s. LPS also produces many types of mediators involved in
septic shock. Of mammals, humans are much more sensitive to LPS than other primates,
and other animals as well (e.g., mice). A dose of 1 μg/kg induces shock in humans, but mice will tolerate a dose up to a thousand times higher. This may relate to differences in the level of circulating natural antibodies between the two species. It may also be linked to multiple immune tactics against pathogens, and part of a multi-faceted anti-microbial strategy that has been informed by human behavioral changes over our species' evolution (e.g., meat eating, agricultural practices, and smoking).
Said et al. showed that LPS causes an
IL-10-dependent inhibition of
CD4 T-cell expansion and function by up-regulating
PD-1
Programmed cell death protein 1 (PD-1), (CD279 cluster of differentiation 279). PD-1 is a protein encoded in humans by the ''PDCD1'' gene. PD-1 is a cell surface receptor on T cells and B cells that has a role in regulating the immune system's re ...
levels on
monocytes
Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also i ...
which leads to IL-10 production by monocytes after binding of PD-1 by
PD-L1
Programmed death-ligand 1 (PD-L1) also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1) is a protein that in humans is encoded by the ''CD274'' gene.
Programmed death-ligand 1 (PD-L1) is a 40kDa type 1 transmembrane prote ...
.
Endotoxins are in large part responsible for the dramatic clinical manifestations of infections with pathogenic Gram-negative bacteria, such as ''
Neisseria meningitidis'', the pathogens that causes
meningococcal disease, including
meningococcemia,
Waterhouse–Friderichsen syndrome, and
meningitis
Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...
.
Portions of the LPS from several bacterial strains have been shown to be chemically similar to human host cell surface molecules; the ability of some bacteria to present molecules on their surface which are chemically identical or similar to the surface molecules of some types of host cells is termed molecular
mimicry
In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. In the simples ...
.
For example, in ''
Neisseria meningitidis'' L2,3,5,7,9, the terminal tetrasaccharide portion of the oligosaccharide (lacto-N-neotetraose) is the same tetrasaccharide as that found in
paragloboside, a precursor for
ABH glycolipid
Glycolipids () are lipids with a carbohydrate attached by a glycosidic (covalent) bond. Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the c ...
antigens found on human
erythrocyte
Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood ce ...
s.
In another example, the terminal trisaccharide portion (lactotriaose) of the oligosaccharide from pathogenic ''
Neisseria'' spp. LOS is also found in lactoneoseries
glycosphingolipids from human cells.
Most meningococci from groups B and C, as well as
gonococci, have been shown to have this trisaccharide as part of their LOS structure.
The presence of these human cell surface 'mimics' may, in addition to acting as a 'camouflage' from the immune system, play a role in the abolishment of
immune tolerance when infecting hosts with certain
human leukocyte antigen
The human leukocyte antigen (HLA) system is a complex of genes on chromosome 6 in humans that encode cell-surface proteins responsible for regulation of the immune system. The HLA system is also known as the human version of the major histo ...
(HLA) genotypes, such as
HLA-B35.
LPS can be sensed directly by
hematopoietic stem cell
Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells. This process is called haematopoiesis. In vertebrates, the first definitive HSCs arise from the ventral endothelial wall of the embryonic aorta within the ...
s (HSCs) through the bonding with TLR4, causing them to proliferate in reaction to a systemic infection. This response activate the TLR4-TRIF-ROS-p38 signaling within the HSCs and through a sustained TLR4 activation can cause a proliferative stress, leading to impair their competitive repopulating ability. Infection in mice using ''
S. typhimurium'' showed similar results, validating the experimental model also ''in vivo''.
Effect of variability on immune response

O-antigens (the outer carbohydrates) are the most variable portion of the LPS molecule, imparting antigenic specificity. In contrast, lipid A is the most conserved part. However, lipid A composition also may vary (e.g., in number and nature of
acyl chains even within or between genera). Some of these variations may impart antagonistic properties to these LPS. For example, diphosphoryl lipid A of ''
Rhodobacter sphaeroides'' (RsDPLA) is a potent antagonist of LPS in human cells, but is an agonist in hamster and equine cells.
It has been speculated that conical lipid A (e.g., from ''
E. coli'') is more agonistic, while less conical lipid A like that of ''Porphyromonas gingivalis'' may activate a different signal (
TLR2 instead of TLR4), and completely cylindrical lipid A like that of ''Rhodobacter sphaeroides'' is antagonistic to TLRs. In general, LPS gene clusters are highly variable between different strains, subspecies, species of bacterial pathogens of plants and animals.
Normal human blood
serum contains anti-LOS antibodies that are bactericidal and patients that have infections caused by serotypically distinct strains possess anti-LOS antibodies that differ in their specificity compared with normal serum.
These differences in humoral immune response to different LOS types can be attributed to the structure of the LOS molecule, primarily within the structure of the oligosaccharide portion of the LOS molecule.
In ''
Neisseria gonorrhoeae'' it has been demonstrated that the antigenicity of LOS molecules can change during an infection due to the ability of these bacteria to synthesize more than one type of LOS,
a characteristic known as
phase variation. Additionally, ''
Neisseria gonorrhoeae'', as well as ''
Neisseria meningitidis'' and ''
Haemophilus influenzae
''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, Motility, non-motile, Coccobacillus, coccobacillary, facultative anaerobic organism, facultatively anaerobic, Capnophile, capnophili ...
'',
are capable of further modifying their LOS ''in vitro'', for example through
sialylation (modification with sialic acid residues), and as a result are able to increase their resistance to
complement-mediated killing
or even down-regulate complement activation
or evade the effects of
bactericidal
A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics.
However, material surfaces can also have bactericidal properties based solely on their p ...
antibodies.
Sialylation may also contribute to hindered
neutrophil
Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in differe ...
attachment and
phagocytosis
Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
by immune system cells as well as a reduced oxidative burst.
''
Haemophilus somnus'', a pathogen of cattle, has also been shown to display LOS phase variation, a characteristic which may help in the evasion of
bovine host immune defenses.
Taken together, these observations suggest that variations in bacterial surface molecules such as LOS can help the pathogen evade both the
humoral (antibody and complement-mediated) and the
cell-mediated (killing by neutrophils, for example) host immune defenses.
Non-canonical pathways of LPS recognition
Recently, it was shown that in addition to
TLR4 mediated pathways, certain members of the family of the
transient receptor potential ion channels recognize LPS. LPS-mediated activation of
TRPA1
Transient receptor potential cation channel, subfamily A, member 1, also known as transient receptor potential ankyrin 1, TRPA1, or The Mustard and Wasabi Receptor, is a protein that in humans is encoded by the ''TRPA1'' (and in mice and rats by ...
was shown in mice and ''
Drosophila melanogaster
''Drosophila melanogaster'' is a species of fly (an insect of the Order (biology), order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly" ...
'' flies. At higher concentrations, LPS activates other members of the sensory
TRP channel family as well, such as
TRPV1
The transient receptor potential cation channel subfamily V member 1 (TRPV1), also known as the capsaicin receptor and the vanilloid receptor 1, is a protein that, in humans, is encoded by the ''TRPV1'' gene. It was the first isolated member of ...
,
TRPM3
Transient receptor potential cation channel subfamily M member 3 is a protein that in humans is encoded by the ''TRPM3'' gene.
Function
The product of this gene belongs to the family of Transient receptor potential channel, transient receptor ...
and to some extent
TRPM8
Transient receptor potential cation channel subfamily M (melastatin) member 8 (TRPM8), also known as the cold and menthol receptor 1 (CMR1), is a protein that in humans is encoded by the ''TRPM8'' gene. The TRPM8 channel is the primary molecular ...
.
LPS is recognized by
TRPV4
Transient receptor potential cation channel subfamily V member 4 is an ion channel protein that in humans is encoded by the ''TRPV4'' gene.
The ''TRPV4'' gene encodes TRPV4, initially named "vanilloid-receptor related osmotically activated chann ...
on epithelial cells. TRPV4 activation by LPS was necessary and sufficient to induce nitric oxide production with a bactericidal effect.
Testing
Lipopolysaccharide is a significant factor that makes bacteria harmful, and it helps categorize them into different groups based on their structure and function. This makes LPS a useful marker for telling apart various Gram-negative bacteria. Swiftly identifying and understanding the types of pathogens involved is crucial for promptly managing and treating infections. Since LPS is the main trigger for the immune response in our cells, it acts as an early signal of an acute infection. Therefore, LPS testing is more specific and meaningful than many other serological tests.
The current methods for testing LPS are quite sensitive, but many of them struggle to differentiate between different LPS groups. Additionally, the nature of LPS, which has both water-attracting and water-repelling properties (amphiphilic), makes it challenging to develop sensitive and user-friendly tests.
The typical detection methods rely on identifying the lipid A part of LPS because Lipid A is very similar among different bacterial species and serotypes. LPS testing techniques fall into six categories, and they often overlap: in vivo tests, in vitro tests, modified immunoassays, biological assays, and chemical assays.
Endotoxin Activity Assay
Because the LPS is very difficult to measure in whole blood and because most LPS is bound to proteins and complement, the Endotoxin Activity Assay (EAA™) was developed and cleared by the US FDA in 2003. EAA is a rapid in vitro chemiluminescent immunodiagnostic test. It utilizes a specific monoclonal antibody to measure the endotoxin activity in EDTA whole blood specimens. This assay uses the biological response of the neutrophils in a patient’s blood to an immunological complex of endotoxin and exogenous antibody – the chemiluminescent reaction formed creates an emission of light. The amount of chemiluminescence is proportional to the logarithmic concentration of LPS in the sample and is a measure of the endotoxin activity in the blood. The assay reacts specifically with the Lipid A moiety of LPS of Gram-negative bacteria and does not cross-react with cell wall constituents of Gram-positive bacteria and other microorganisms.
Pathophysiology
LPS is a powerful toxin that, when in the body, triggers inflammation by binding to cell receptors. Excessive LPS in the blood, endotoxemia, may cause a highly lethal form of sepsis known as endotoxic septic shock.
This condition includes symptoms that fall along a continuum of pathophysiologic states, starting with a systemic inflammatory response syndrome (SIRS) and ending in multiorgan dysfunction syndrome (MODS) before death. Early symptoms include rapid heart rate, quick breathing, temperature changes, and blood clotting issues, resulting in blood vessels widening and reduced blood volume, leading to cellular dysfunction.
Recent research indicates that even small LPS exposure is associated with autoimmune diseases and allergies. High levels of LPS in the blood can lead to metabolic syndrome, increasing the risk of conditions like diabetes, heart disease, and liver problems.
LPS also plays a crucial role in symptoms caused by infections from harmful bacteria, including severe conditions like Waterhouse-Friderichsen syndrome, meningococcemia, and meningitis. Certain bacteria can adapt their LPS to cause long-lasting infections in the respiratory and digestive systems.
Recent studies have shown that LPS disrupts cell membrane lipids, affecting cholesterol and metabolism, potentially leading to high cholesterol, abnormal blood lipid levels, and non-alcoholic fatty liver disease. In some cases, LPS can interfere with toxin clearance, which may be linked to neurological issues.
Health effects
In general the health effects of LPS are due to its abilities as a potent activator and modulator of the immune system, especially its inducement of inflammation. LPS is directly cytoxic and is highly immunostimulatory – as host immune cells recognize LPS, complement are strongly activated. Complement activation and a rising anti-inflammatory response can lead to immune cell dysfunction, immunosuppression, widespread coagulopathy, and serious tissue damage, and can progress to multi-system organ failure and death.
Endotoxemia
The presence of endotoxins in the blood is called endotoxemia. High level of endotoxemia can lead to
septic shock,
or more specifically endotoxic septic shock,
while lower concentration of endotoxins in the bloodstream is called metabolic endotoxemia.
Endotoxemia is associated with obesity, diet,
cardiovascular diseases,
and diabetes,
while also host genetics might have an effect.
Moreover, endotoxemia of intestinal origin, especially, at the
host-pathogen interface, is considered to be an important factor in the development of alcoholic hepatitis, which is likely to develop on the basis of the
small bowel bacterial overgrowth syndrome and an increased
intestinal permeability.
Lipid A may cause uncontrolled activation of mammalian immune systems with production of
inflammatory mediators that may lead to endotoxic
septic shock.
This
inflammatory reaction is primarily mediated by
Toll-like receptor 4 which is responsible for immune system cell activation.
Damage to the
endothelial layer of blood vessels caused by these
inflammatory mediators can lead to
capillary leak syndrome, dilation of blood vessels and a decrease in cardiac function and can further worsen shock.
LPS is also a potent activator of complemen.
Uncontrolled complement activation may trigger destructive endothelial damage leading to
disseminated intravascular coagulation
Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking Microvessel, small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems ...
(DIC), or
atypical hemolytic uremic syndrome (aHUS) with injury to various organs such as including kidneys and lungs. The skin can show the effects of vascular damage often coupled with depletion of coagulation factors in the form of
petechiae,
purpura and
ecchymoses. The limbs can also be affected, sometimes with devastating consequences such as the development of
gangrene, requiring subsequent
amputation
Amputation is the removal of a Limb (anatomy), limb or other body part by Physical trauma, trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as cancer, malign ...
.
Loss of function of the adrenal glands can cause
adrenal insufficiency
Adrenal insufficiency is a condition in which the adrenal glands do not produce adequate amounts of steroid hormones. The adrenal glands—also referred to as the adrenal cortex—normally secrete glucocorticoids (primarily cortisol), mineraloco ...
and additional
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, ...
into the adrenals causes
Waterhouse-Friderichsen syndrome, both of which can be life-threatening.
It has also been reported that
gonococcal LOS can cause damage to human
fallopian tube
The fallopian tubes, also known as uterine tubes, oviducts or salpinges (: salpinx), are paired tubular sex organs in the human female body that stretch from the Ovary, ovaries to the uterus. The fallopian tubes are part of the female reproduct ...
s.
Treatment of Endotoxemia
Toraymyxin is a widely used extracorporeal endotoxin removal therapy through direct hemoadsorption (also referred to as
hemoperfusion). It is a polystyrene-derived cartridge with molecules of
polymyxin B (PMX-B) covalently bound to mesh fibers contained within it. Polymyxins are cyclic cationic polypeptide antibiotics derived from ''
Bacillus polymyxa'' with an effective antimicrobial activity against Gram-negative bacteria, but their intravenous clinical use has been limited due to their nephrotoxicity and neurotoxicity side effects. The extracorporeal use of the Toraymyxin cartridge allows PMX-B to bind lipid A with a very stable interaction with its hydrophobic residues thereby neutralizing endotoxins as the blood is filtered through the extracorporeal circuit inside the cartridge, thus reversing endotoxemia and avoiding its toxic systemic effects.
Auto-immune disease
The
molecular mimicry of some LOS molecules is thought to cause autoimmune-based host responses, such as flareups of
multiple sclerosis
Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...
.
Other examples of bacterial mimicry of host structures via LOS are found with the bacteria ''
Helicobacter pylori
''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...
'' and ''
Campylobacter jejuni
''Campylobacter jejuni'' is a species of pathogenic bacteria that is commonly associated with poultry, and is also often found in animal feces. This species of microbe is one of the most common causes of food poisoning in Europe and in the US, w ...
'', organisms which cause gastrointestinal disease in humans, and ''
Haemophilus ducreyi'' which causes
chancroid
Chancroid ( ) is a bacterial sexually transmitted infection characterized by painful sores on the genitalia. Chancroid is known to spread from one individual to another solely through sexual contact. However, there have been reports of accidenta ...
. Certain ''C. jejuni'' LPS serotypes (attributed to certain tetra- and pentasaccharide moieties of the core oligosaccharide) have also been implicated with
Guillain–Barré syndrome
Guillain–Barré syndrome (GBS) is a rapid-onset Paralysis, muscle weakness caused by the immune system damaging the peripheral nervous system. Typically, both sides of the body are involved, and the initial symptoms are changes in sensation ...
and a variant of Guillain–Barré called
Miller-Fisher syndrome.
Link to obesity
Epidemiological studies have shown that increased endotoxin load, which can be a result of increased populations of endotoxin-producing bacteria in the intestinal tract, is associated with certain obesity-related patient groups.
Other studies have shown that purified endotoxin from ''
Escherichia coli
''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...
'' can induce obesity and insulin-resistance when injected into germ-free
mouse models.
A more recent study has uncovered a potentially contributing role for ''
Enterobacter cloacae
''Enterobacter cloacae'' is a clinically significant Gram-negative, facultatively-anaerobic, rod-shaped bacterium.
Microbiology
In microbiology laboratories, ''E. cloacae'' is frequently grown at 30 °C on nutrient agar or at 35 ...
'' B29 toward obesity and insulin resistance in a human patient.
The presumed mechanism for the association of endotoxin with obesity is that endotoxin induces an inflammation-mediated pathway accounting for the observed obesity and insulin resistance.
Bacterial genera associated with endotoxin-related obesity effects include ''
Escherichia
''Escherichia'' ( ) is a genus of Gram-negative, non-Endospore, spore-forming, Facultative anaerobic organism, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastroin ...
'' and ''
Enterobacter
''Enterobacter'' is a genus of common Gram-negative, Facultative anaerobic organism, facultatively anaerobic, bacillus (shape), rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae. Cultures are found in soil, water, sewage, ...
.''
Depression
There is experimental and observational evidence that LPS might play a role in depression. Administration of LPS in mice can lead to depressive symptoms, and there seem to be elevated levels of LPS in some people with depression. Inflammation may sometimes play a role in the development of depression, and LPS is pro-inflammatory.
Cellular senescence
Inflammation induced by LPS can induce
cellular senescence
Cellular senescence is a phenomenon characterized by the cessation of cell division. In their experiments during the early 1960s, Leonard Hayflick and Paul Moorhead found that normal human fetal fibroblasts in culture reach a maximum of appro ...
, as has been shown for the lung
epithelial cells and
microglial cells (the latter leading to
neurodegeneration
A neurodegenerative disease is caused by the progressive loss of neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their cell death, death. Neurodegenerative diseases include amyotrophic lateral sc ...
).
Role as contaminant in biotechnology and research
Lipopolysaccharides are frequent contaminants in
plasmid
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria and ...
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
prepared from bacteria or proteins expressed from bacteria, and ''must'' be removed from the DNA or protein to avoid contaminating experiments and to avoid toxicity of products manufactured using
industrial fermentation
Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity ch ...
.
Ovalbumin is frequently contaminated with endotoxins. Ovalbumin is one of the extensively studied proteins in animal models and also an established model allergen for airway hyper-responsiveness (AHR). Commercially available ovalbumin that is contaminated with LPS can falsify research results, as it does not accurately reflect the effect of the protein antigen on animal physiology.
In pharmaceutical production, it is necessary to remove all traces of endotoxin from drug product containers, as even small amounts of endotoxin will cause illness in humans. A
depyrogenation oven is used for this purpose. Temperatures in excess of 300 °C are required to fully break down LPS.
The standard
assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...
for detecting presence of endotoxin is the
Limulus Amebocyte Lysate (LAL) assay, utilizing blood from the
Horseshoe crab
Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scor ...
(''Limulus polyphemus'').
Very low levels of LPS can cause coagulation of the limulus lysate due to a powerful amplification through an enzymatic cascade. However, due to the dwindling population of horseshoe crabs, and the fact that there are factors that interfere with the LAL assay, efforts have been made to develop alternative assays, with the most promising ones being
ELISA
The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...
tests using a
recombinant version of a protein in the LAL assay, Factor C.
See also
*
Bioaerosol
Bioaerosols (short for biological aerosols) are a subcategory of particles released from terrestrial and marine ecosystems into the atmosphere. They consist of both living and non-living components, such as fungi, pollen, bacteria and viruses. Comm ...
*
Depyrogenation
*
Host-pathogen interface
*
Mucopolysaccharide
*
Nesfatin-1
*
Schwartzman reaction
*
AOAH
References
External links
*
{{Toxins
Membrane-active molecules
Saccharolipids
Bacterial toxins