Regulatory roles for FcgammaRIII (CD16) and FcgammaRII (CD32) in the development of T- and B-lineage lymphoid cells.

IgG Fc receptors (FcgammaR) occur on all hematopoietic lineages and participate in a diversity of functions that reflect the combined effects of the molecular heterogeneity of FcgammaR and the inherent specialization of the FcgammaR+ cells. An extensive literature describes the functions of FcgammaR on mature myeloid and lymphoid cells in humans and mice but little has been published about FcgammaR on lineage progenitor cells. Several studies suggest that FcgammaR can influence leukocyte development and that FcgammaRII (CD32) and FcgammaRIII (CD16) can regulate murine T- and B-lineage development at stages before the expression of clonal antigen receptors. The nominal ligand of FcgammaR is IgG and the physiologically relevant ligand is the IgG-antigen complex, but it is also known that alternative, non-Ig ligands exist for Fc receptors. A role for FcgammaR in the regulation of leukocyte development has potential relevance for clinical situations in which the levels of nominal and/or alternative ligands of FcgammaR are elevated, or the production of soluble forms of FcgammaR is increased.