Fc receptors and Ia antigens.

Antibody against Ia antigens inhibits the ability of B lymphocytes to bind aggregated immunoglobulin and to form EA rosettes. The explanation suggested for this phenomenon has been that Ia antigens are identical to or closely associated with Fc receptors. But a variety of observations preclude acceptance of this explanation since inhibition is also demonstrable with antibody against a wide variety of B cell surface components, including H-2K, H-2D, beta2 microglobulin, immunoglobulin, Ly 4.2. Furthermore, Fc receptor function can be separated from Ia antigens by capping or by isolation of membrane components. It seems likely that the mechanism of inhibition of Fc receptors by antibody against Ia antigens is part of a broader spectrum of effects induced when antibody binds to cell membrane antigens.