Fc alpha receptor (FcαR) is the receptor specific for IgA which binds IgA with low affinity. There is only one type belonging to the Fc alpha receptor subgroup, which is called FcαRI (CD89). Fc alpha receptor I is expressed on neutrophils, eosinophils, monocytes/macrophages, dendritic cells and Kupffer cells.
A number of cytokines and other agents modulate Fc alpha receptor I expression, such as IL-1β, IL-8, THF-α. In contrast to other Fc receptors, Fc alpha receptor I expression is downregulated by polymeric IgA.
Fc alpha receptor is a member of the multichain immune recognition receptor (MIRR) family. Fc alpha receptor is composed of two extracellular Ig-like domains, α-chain and γ-chain. Fc alpha receptor I γ-chain contains a so-called ITAM (immunoreceptor tyrosine-based activation motif) signaling motif. Fc alpha receptor I with ITAM activates sequentially src family tyrosine kinases and syk family tyrosine kinases and mediates endocytosis, ADCC and recyling of IgA. Signaling is dependent on association of FcαRI with another FcαRI γ-chain subunit, forming the trimmer FcαRIα/γγ.