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IC3b
iC3b is a protein fragment that is part of the complement system, a component of the vertebrate immune system. iC3b is produced when complement factor I cleaves C3b.Robbins Basic Pathology 8th ed 2007. R Cotran, S Robbins, V Kumar, J Perkins. W.B. Saunders Company. Complement receptors on white blood cells are able to bind iC3b, so iC3b functions as an opsonin Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound. Thus, opsonins act as tags to label things in the body that should be phagocytosed (i.e. .... Unlike intact C3b, iC3b cannot associate with factor B, thus preventing amplification of the complement cascade through the alternative pathway. Complement factor I can further cleave iC3b into a protein fragment known as C3d. References * {{biochemistry-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Complement Receptors
A complement receptor is a membrane-bound receptor belonging to the complement system, which is part of the innate immune system. Complement receptors bind effector protein fragments that are produced in response to antigen-antibody complexes or damage-associated molecules. Complement receptor activation contributes to the regulation of inflammation, leukocyte extravasation, and phagocytosis; it also contributes to the adaptive immune response. Different complement receptors can participate in either the classical complement pathway, the alternative complement pathway, or both. Expression and function White blood cells, particularly monocytes and macrophages, express complement receptors on their surface. All four complement receptors can bind to fragments of complement component 3 or complement component 4 coated on pathogen surface, but the receptors trigger different downstream activities. Complement receptor (CR) 1, 3, and 4 function as opsonins which stimulate phagocytosi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Complement System
The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. It is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime. The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system. The complement system consists of a number of small proteins that are synthesized by the liver, and circulate in the blood as inactive precursors. When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The end result of this ''complement activation'' or ''complement fixation'' cascade is stimulation of phagocytes to clear foreign and damaged materi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opsonin
Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound. Thus, opsonins act as tags to label things in the body that should be phagocytosed (i.e. eaten) by phagocytes (cells that specialise in phagocytosis, i.e. cellular eating). Different types of things ("targets") can be tagged by opsonins for phagocytosis, including: pathogens (such as bacteria), cancer cells, aged cells, dead or dying cells (such as apoptotic cells), excess synapses, or protein aggregates (such as amyloid plaques). Opsonins help clear pathogens, as well as dead, dying and diseased cells. Opsonins were discovered and named "opsonins" in 1904 by Wright and Douglas, who found that incubating bacteria with blood plasma enabled phagocytes to phagocytose (and thereby destroy) the bacteria. They concluded that: “We have here conclusive proof that the blood fluids modify the bacteria in a manner which renders them ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Complement Cascade
The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. It is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime. The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system. The complement system consists of a number of small proteins that are synthesized by the liver, and circulate in the blood as inactive precursors. When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The end result of this ''complement activation'' or ''complement fixation'' cascade is stimulation of phagocytes to clear foreign and damaged materia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Complement Factor I
Complement factor I, also known as C3b/C4b inactivator, is a protein that in humans is encoded by the ''CFI'' gene. Complement factor I (factor I) is a protein of the complement system, first isolated in 1966 in guinea pig serum, that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b. It is a soluble glycoprotein that circulates in human blood at an average concentration of 35 μg/mL. Synthesis The gene for Factor I in humans is located on chromosome 4. Factor I is synthesized mostly in the liver, but also in monocytes, fibroblasts, keratinocytes, and endothelial cells. When synthesized, it is a 66kDa polypeptide chain with N-linked glycans at 6 positions. Then, factor I is cleaved by furin to yield the mature factor I protein, which is a disulfide-linked dimer of heavy chain (residues 19-335, 51 kDalton) and light chain (residues 340-583, 37 kDalton). Only the mature protein is active. Structure Factor I is a glycoprotein heterodimer c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alternative Pathway
The alternative pathway is a type of cascade reaction of the complement system and is a component of the innate immune system, a natural defense against infections. The alternative pathway is one of three complement pathways that opsonize and kill pathogens. The pathway is triggered when the C3b protein directly binds a microbe. It can also be triggered by foreign materials and damaged tissues. Cascade This change in shape allows the binding of plasma protein Factor B, which allows Factor D to cleave Factor B into Ba and Bb. Bb remains bound to C3(H2O) to form C3(H2O)Bb. This complex is also known as a fluid-phase C3-convertase. This convertase, the alternative pathway C3-convertase, although only produced in small amounts, can cleave multiple C3 proteins into C3a and C3b. The complex is believed to be unstable until it binds properdin, a serum protein. The addition of properdin forms the complex C3bBbP, a stable compound which can bind an additional C3b to form alterna ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Immune System
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions. Nearly all organisms have some kind of immune system. Bacteria have a rudimentary immune system in the form of enzymes that protect against virus infections. Other basic immune mechanisms evolved in ancient plants and animals and remain in their modern descendants. These mechanisms include phagocytosis, antimicrobial ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
White Blood Cells
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system. All white blood cells have nuclei, which distinguishes them from the other blood cells, the anucleated red blood cells (RBCs) and platelets. The different white blood cells are usually classified by cell lineage (myeloid cells or lymphoid cells). White blood cells are part of the body's immune system. They help the body fight infection and other diseases. Types of white blood cells are granulocytes (neutrophils, eosinophils, and basophils), and agranulocytes (monocytes, and lymphocytes (T cells and B cells)). Myeloid cells ( myelocytes) include neutrophils, eosinophils, mast cells, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Factor B
Complement factor B is a protein that in humans is encoded by the ''CFB'' gene. Function This gene encodes complement factor B, a component of the alternative pathway of complement activation. Factor B circulates in the blood as a single chain polypeptide. Upon activation of the alternative pathway, it is cleaved by complement factor D yielding the noncatalytic chain Ba and the catalytic subunit Bb. The active subunit Bb is a serine protease that associates with C3b to form the alternative pathway C3 convertase. Bb is involved in the proliferation of preactivated B lymphocytes, while Ba inhibits their proliferation. This gene localizes to the major histocompatibility complex ( MHC class III) region on chromosome 6. This cluster includes several genes involved in regulation of the immune reaction. The polyadenylation site of this gene is 421 bp from the 5' end of the gene for complement component 2. References Further reading * * * * * * * * * * * * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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