Basic science for the clinician 47[corrected]: Fcgamma receptors

It is said that a gun has only one "business end" but not so for antibodies. The end with the antigen binding sites (the Fab) certainly has gained a great deal of deserved attention; this is, after all, where the humoral immune system uses its much vaunted "antigen specificity" to engage the outside (and sometimes, unfortunately, the inside) world. The other end (Fc--no the "c" does not stand for "constant," it stands for "crystallizable" because that part of rabbit IgG crystallized for the initial investigators) consists of the other end of heavy chain of the immunoglobulin chains, bearing markers that define an antibody as IgG, IgA, IgM, IgE, or IgD. The Fc component contains sequences that have the capacity to undertake a number of biologic activities, most of which, aside from complement fixation, depend upon the Fc component attaching to a cell via that cell's Fc receptors. Fc receptors (FcR) come in a number of specificities (defined by the Fc they bind and by the status of that Fc) and have different functions which are worthy of attention in this series. This report focused on the various FcgammaR, the receptors for IgG.