Fc (Ig constant fragment) receptors ensure protection of the host against foreign antigens, such as microorganisms and pathogens, by removing Ig-coated antigen complexes from circulation. Fc receptors are present on lymphoid and myeloid derivatives, where they mediate endocytosis of Ig-antigen complexes, antibody production in B cells through T cell antigen presentation, cytotoxicity and the release of cytokines and reactive oxygen species. CD89, also known as Immunoglobulin alpha Fc receptor (Fc alpha RI), is a glycoprotein that is expressed on the surface of neutrophils, monocytes, macrophages and eosinophils and is a potent cytotoxic trigger molecule. CD89 specifically interacts with aggregated IgAs, not IgG. Cytokines can initiate a high-binding state for CD89 through a mechanism that involves the intracellular C-terminus of CD89. Polymorphisms within the gene encoding CD89 may be associated with susceptibility to IgA nephropathy, a form of glomerulonephritis characterized by IgA antibody deposition in the kidney glomerulus.
