Eat-me signals are molecules exposed on the surface of a cell to induce
phagocytes to
phagocytose (eat) that cell.
Currently known eat-me signals include:
phosphatidylserine, oxidized
phospholipid
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s,
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, fructose, and galactose. Compound sugars, also called disaccharides or double ...
residues (such as
galactose),
deoxyribonucleic acid (DNA),
calreticulin,
annexin A1,
histones and
pentraxin-3 (PTX3).
The most well characterised eat-me signal is the phospholipid phosphatidylserine. Healthy cells do not expose phosphatidylserine on their surface, whereas dead, dying, infected, injured and some activated cells expose phosphatidylserine on their surface in order to induce phagocytes to phagocytose them.
Most
glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...
s and
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 connec ...
s on the surface of our cells have short sugar chains that terminate in
sialic acid Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone.
The term "sialic acid" (from the Greek for saliva, - ''sÃalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this gr ...
residues, which inhibit
phagocytosis, but removal of these residues reveals galactose residues (and subsequently
N-acetylglucosamine
''N''-Acetylglucosamine (GlcNAc) is an amide derivative of the monosaccharide glucose. It is a secondary amide between glucosamine and acetic acid. It is significant in several biological systems.
It is part of a biopolymer in the bacterial ...
and
mannose residues) that can bind
opsonins or directly activate phagocytic receptors.
Calreticulin, annexin A1, histones, pentraxin-3 and DNA may be released by (and onto the surface of) dying cells to encourage phagocytes to eat these cells, thereby acting as self-opsonins.
Eat-me signals, or the opsonins that bind them, are recognised by phagocytic receptors on phagocytes, inducing engulfment of the cell exposing the eat-me signal.
See also
*
Find-me signals
References
{{reflist
Cell biology
Cellular senescence