Host defense receptors refer to a series of receptors that play a key role in adaptive cellular and humoral immune responses, such as complement receptors, Fc receptors (linking pattern), toll-like receptors, killer cell immunoglobulin-like receptors with lectin-like receptors and leukocyte immunoglobulin-like receptors, etc. These receptors are effective targets for the treatment of many diseases. Here we focus on complement receptors and toll-like receptors.
Complement receptor (CR) is a surface glycoprotein on the cell membrane that can specifically bind to complement components or complement fragments. Many types of cell membranes have complement receptors, and the same cell membrane can contain different receptors. Complement receptors are named CR1, CR2, CR3 and CR4 in order of their discovery. In addition, there are other receptors for complement components, such as Ciq receptors, C3a receptors, C5a receptors, etc. Among them, CR1-CR4 are all C3 series fragment receptors, and they are also the most studied complement receptors. CR1-CR4 does not recognize circulating C3 molecules and only selectively binds fragments after C3 cleavage.
The cell types of receptor distribution of different fragments are different. CR1 (C3b receptor), also known as CD35, is widely distributed and can be found on human erythrocytes, neutrophils, monocytes-macrophages and B cells.
CR2 (C3d receptor) also known as CD21, is only expressed on lymphoblasts and lymphocytes. It is the Epstein-Barr virus receptor on B cells. The CR2 ligands are C3dg, C3d, Ic3b according to their affinity. Although C3b has low affinity, it can also react with it.
CR3 (iC3b receptor), also known as CD11b, is only expressed on phagocytes, and its ligand is iC3b, but CR1, CR2, and iC3b also react, and CR3 requires the presence of divalent ions when binding to the ligand.
CR4, also known as CD11c, is highly expressed by neutrophils and monocytes-macrophages. Its ligand is iC3b, but monoclonal antibodies against other complement receptors cannot block the binding of CR4 to iC3b, proving the existence of CR4.
Toll-like receptors (TLRs) are pattern recognition receptors that recognize special substances released by invading bacteria and viruses, such as lipopolysaccharide, mannose, teichoic acid, and peptidoglycan, which play a key role in the innate immune response. Its name derives from homology with the Drosophila Toll gene; in contrast to adaptive immunity, which evolved in the vertebrate lineage, innate immunity exists (and is conserved) in the invertebrate branch. TLRs are a superfamily of single-pass transmembrane receptors that are expressed in various tissues and many different cell types, and 11 family members have been identified. Among them, TLR1, TLR2, TLR4, TLR5, TLR6 and TLR11 are located on the cell surface, while TLR3, TLR7, TLR8 and TLR9 are located in the endosomal/lysosomal compartment. Highly expressed in dendritic cells and macrophages, these receptors sense and respond to pathogen-associated molecular patterns (PAMPs) and activate first-line defense inflammatory responses through subsequent intracellular signaling pathways. Activation of TLRs (biomolecules that trigger cascades in host cells) via damage-associated molecular patterns (DAMPs) has been demonstrated to promote tumor growth and build tumor tolerance to the host immune response.
CUSABIO has listed some popular targets related host defense receptor. Click on the corresponding target to view all the reagents related to the target.
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