An Introduction to Receptors

Receptors are proteins, usually cell surface receptors, which bind to ligands and cause responses in the immune system, including cytokine receptors, growth factor receptors and Fc receptor. Receptors can be found in various immune cells like B cells, T cells, NK cells, monocytes and stem cells. A molecule that binds to a receptor is called a ligand, and can be a peptide (short-protein) or another small molecule such as a neurotransmitter, hormone, pharmaceutical-drug, toxin, or parts of the outside of a virus or microbe. When a ligand binds to its corresponding receptor, it activates or inhibits the receptor's associated-biochemical pathway.

Receptors can induce cell growth, division and death; control membrane channels or regulate cell binding. Receptors play an important role in signal transduction, immunetherapy and immune responses.

Growth factors and their receptors play important roles in the regulation of cell division, development and differentiation. Growth factor receptors include wnt receptor, tie, neurotrophin receptor, ephrin receptor, insulin-like growth factor receptor (IGF receptor), epidermal growth factor receptor (EGF receptor), fibroblast growth factor receptor (FGF receptor), platelet-derived growth factor receptor (PDGF receptor) and vascular endothelial growth factor receptor (VEGF receptor), etc.

The patterns of expression of cytokine receptors are a product of differentiation and provide for changes in physiological regulation. These cytokine receptors enable cells to communicate with the extracellular environment by responding to signals generated in the vicinity or in other parts of the organism. Thus, the initial binding of cytokines to their receptors is a key event that occurs rapidly, at very low cytokine concentrations, is usually virtually irreversible, and leads to intracellular changes resulting in a biologic response. The biologic response can vary between cytokine receptors and from cell to cell but in general it involves gene expression, changes in the cell cycle, and release of mediators such as cytokines themselves.

B cell, also called B lymphocyte, developed in bone marrow of most mammals, that circulates in the blood and lymph. One of the main functions of a B cell is antibody production, which aids in adaptive immunity, complement activation, and induction of allergic responses.

The T cell antigen receptor (TCR) is the principle defining marker of all T cells. Also associated with the TCR is a complex of proteins known as CD3, which participate in the transduction of an intracellular signal following TCR binding to its cognate MHC/antigen complex. With the help of chemokine receptor CCR5 or CXCR4, HIV binds CD4 and penetrates its nucleic acid into the host cell. This cause CD4 T-cell destruction and immune system collapse.

Granulocyte is a type of immune cell that has granules with enzymes released during infections, allergic reactions and asthma. A granulocyte is a type of white blood cell. Neutrophils, eosinophils, and basophils are three different forms of granulocytes. Granulocytes are crucial players in innate and adaptive immunity that express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine receptors, Fc-receptors, various cytokine receptors, as well as innate immune receptors such as toll-like receptors and C-type lectins.

Receptors References

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Akira, S., Uematsu, S., & Takeuchi, O. (2006). Pathogen recognition and innate immunity. Cell, 124(4), 783-801.

Clark, M. R., Campbell, K. S., Kazlauskas, A., Johnson, S. A., Hertz, M., Potter, T. A., ... & Cambier, J. C. (1992). The B cell antigen receptor complex: association of Ig-alpha and Ig-beta with distinct cytoplasmic effectors. Science, 258(5079), 123-126.

Ihle, J. N. (1995). Cytokine receptor signalling. Nature, 377(6550), 591-594.

Yao, Z., Fanslow, W. C., Seldin, M. F., Rousseau, A. M., Painter, S. L., Comeau, M. R., ... & Spriggs, M. K. (1995). Herpesvirus Saimiri encodes a new cytokine, IL-17, which binds to a novel cytokine receptor. Immunity, 3(6), 811-821.