CD32: Иммундық жауаптар мен қабынудағы рөлі

Surface receptor glycoprotein
the molecule

CD32 (cluster of differentiation 32), also known as FcγRII or FCGR2, is a surface receptor glycoprotein belonging to the Ig gene superfamily. CD32 can be found on the surface of a variety of immune cells. CD32 has a low affinity for the Fc region of IgG antibodies in monomeric form, but high affinity for IgG immune complexes. CD32 has two major functions: cellular response regulation, and the uptake of immune complexes. In humans, there are three major CD32 subtypes: CD32A, CD32B, and CD32C. While CD32A and CD32C are involved in activating cellular responses, CD32B is inhibitory. however, the high degree of homology between the extracellular domains of CD32A and CD32C make differentiation difficult.

CD32A is an activating subtype of CD32 that can be found on a variety of immune cells notably, CD32A is found on platelets, neutrophils, macrophages, and dendritic cells (DCs). On platelets, it is known to aid in the internalization of IgG opsonized Escherichia coli, and it is more generally implicated in mediating bacterial activated platelet responses. Thus, CD32B plays an important role in both antibody and memory immune responses. The balance between CD32B and its activating counterparts is crucial to appropriate cell function. Having too little CD32B has been associated with dysregulated antibody function, as well as increased antibody dependent inflammatory cell responses. Some individuals inheriting mutated, inactivate CD32B genes have a reduced risk of contracting malaria; this is attributed to an enhancement of FcR dependent phagocytic functions. CD32B imbalance is also associated with autoimmunity. CD32B deficient mice have been found to be more susceptible to immune complex mediated autoimmunity. Likewise, systemic lupus erythematosus (SLE) in humans is associated with a decrease in CD32B on the surface of memory B cells. A decrease on dendritic cells is often found in patients with rheumatoid arthritis. The therapeutic usage of monoclonal antibodies against CD32B can be effective for inducing cytotoxicity against B cell lymphoma cells. CD32B is also found on basophils, neutrophils, monocytes, and macrophages.

CD32B can be found on airway smooth muscle cells, as well as liver sinusoidal endothelial cells and salivary gland epithelial cells.

CD32C is expressed in ~20% of the human population, and is not well understood. It can be found on B cells and natural killer (NK) cells. When expressed, CD32C plays an important role in the activation of antibody dependent cell cytotoxicity (ADCC). Animal studies have linked CD32C to augmentation of pathological inflammatory responses.