Regulatory roles for Fc gamma RIII (CD16) and Fc gamma RII (CD32) in the development of T- and B-lineage lymphoid cells

IgG Fe receptors (Fc gamma R) occur on all hematopoietic lineages and parti cipate in a diversity of functions that reflect the combined effects of the molecular heterogeneity of Fc gamma R and the inherent specialization of t he Fc gamma R+ cells. An extensive literature describes the functions of Fc gamma R on mature myeloid and lymphoid cells in humans and mice but little has been published about Fc gamma R on lineage progenitor cells, Several s tudies suggest that Fc gamma R can influence leukocyte development and that Fc gamma RII (CD32) and Fc gamma RIII (CD16) can regulate murine T- and B- lineage development at stages before the expression of clonal antigen recep tors. The nominal ligand of Fc gamma R is IgG and the physiologically relev ant ligand is the IgG-antigen complex, but it is also known that alternativ e, non-Ig ligands exist for Fc receptors. A role for Fc gamma R in the regu lation of leukocyte development has potential relevance for clinical situat ions in which the levels of nominal and/or alternative ligands of Fc gamma R are elevated, or the production of soluble forms of Fc gamma R is increas ed.