Scavenger receptor (immunology)

Scavenger receptors are a large and diverse superfamily of cell surface receptors. Its properties were first recorded in 1970 by Drs. Brown and Goldstein, with the defining property being the ability to bind and remove modified low density lipoproteins (LDL). Today scavenger receptors are known to be involved in a wide range of processes, such as: homeostasis, apoptosis, inflammatory diseases and pathogen clearance. Scavenger receptors are mainly found on myeloid cells and other cells that bind to numerous ligands, primarily endogenous and modified host-molecules together with pathogen-associated molecular patterns(PAMPs), and remove them. The Kupffer cells in the liver are particularly rich in scavenger receptors, includes SR-A I, SR-A II, and MARCO.
Function.
The scavenger receptor superfamily is defined by its ability to recognize and bind a broad range of common ligands. These ligands include: polyanionic ligands including lipoproteins, apoptotic cells, cholesterol ester, phospholipids, proteoglycans, ferritin, and carbohydrates. This broad recognition range allows scavenger receptors to play an important role in homeostasis and the combating of diseases. This is accomplished via the recognition of various PAMP's and DAMP's, which leads to the removal or scavenging of pathogens with the recognition of PAMP's and the removal of apoptotic cells, self reactive antigens and the products of oxidative stress.
In atherosclerotic lesions, macrophages that express scavenger receptors on their plasma membrane take up the oxidized LDL deposited in the blood vessel wall aggressively, and develop into foam cells. Likewise, they secrete various inflammatory cytokines and accelerate the development of atherosclerosis.
Types.
Scavenger receptors are incredibly diverse and therefore, organized into many different classes, starting at A and continuing to L. This organization is based on their structural properties. Due to the diversity and ongoing research into scavenger receptors, the receptors lack an accepted nomenclature and have been described under different names. In 2014 a new nomenclature was proposed that has been used by some researchers, although no official recognition has been given.
Class A.
Class A receptors are a type II membrane protein who use their collagen-like domain for ligand binding.
Members include:Scavenger receptors type 1 (SR-A1), which is a trimer with a molecular weight of about 220-250 kDa (the molecular weight of monomeric protein is about 80 kDa). It preferentially binds modified LDL, either acylated (acLDL) or oxidized (oxLDL). Other ligands include: β-amyloid, heat shock proteins, surface molecules of Gram-positive and Gram-negative bacteria, hepatitis C virus.
SR-A1 can be alternatively spliced to generate a truncation at the C-terminus; it is contained within the Endoplasmatic Reticulum, and just like the unspliced version, has a strong affinity for polyanionic ligand binding.
Class B.
CD36 and scavenger receptor class BI are identified as genes encoding for oxidized LDL receptors and classified into scavenger receptor B (SR-B). Both proteins have two transmembrane domains with an extracellular loop, and they are concentrated in a specific plasma membrane microdomain, the caveolae.
Members include:
Other.
Some receptors that can bind to oxidized LDL have been discovered. 