The Diverse Functions of the Ubiquitous Fcγ Receptors and Their Unique Constituent, FcRγ Subunit

Fc gamma receptors (Fc gamma Rs) are widely expressed on a variety of immune cells and play a myriad of regulatory roles in the immune system because of their structural diversity. Apart from their indispensable role in specific binding to the Fc portion of antibody subsets, Fc gamma Rs manifest diverse biological functions upon binding to their putative ligands. Examples of such manifestation include phagocytosis, presentation of antigens, mediation of antibody-dependent cellular cytotoxicity, anaphylactic reactions, and the promotion of apoptosis of T cells and natural killer cells. Functionally, the equilibrium between activating and inhibiting Fc gamma R maintains the balance between afferent and efferent immunity. The gamma subunit of the immunoglobulin Fc receptor (FcR gamma) is a key component of discrete immune receptors and Fc receptors including the Fc gamma R family. Furthermore, Fc gamma Rs exert a key role in terms of crosslinking the innate and adaptive workhorses of immunity. Ablation of one of these receptors might positively or negatively influence the immune response. Very recently, we discovered that FcR gamma derived from natural cytotoxicity triggering receptor 1 (NCR1) curtails CD8(+) T cell expansion and thereby turns an acute viral infection into a chronic one. Such a finding opens a new avenue for targeting the Fc gamma Rs as one of the therapeutic regimens to boost the immune response. This review highlights the structural heterogeneity and functional diversity of the ubiquitous Fc gamma Rs along with their featured subunit, FcR gamma.