Isotype Specific Immunoregulation: Role of FcαR⁺ T Cells and IBFα in IgA Responses

Abstract

T cell subsets which express Fc receptors for immunoglobulin (FcR) are important in isotype-specific regulation of B cell responses (1). These FcR⁺ T cells secrete isotype-specific immunoglobulin binding factors (IBF) which recognize specific Fc regions of immunoglobulin (Ig) and IBF can up or down regulate B cell antibody synthesis in these Ig classes. In this regard, allo-activated T cells which bear Fc receptors for IgG (FcγR) and the T2D4 T cell line (FcγR⁺ and FcαR⁺) release IgG binding factor (IBFγ) and suppress this isotype for in vitro responses (2). In the IgE system, Fc receptors for IgE (FcεR) occur on T cells which regulate this isotype response via production of either enhancing or suppressive IgE binding factors (IBFε) (3). Both potentiating and suppressive IBFε are similar in size (Mr ~15,000). They contain a common protein core, and the degree of glycosylation determines whether IBFε enhances or suppresses the IgE responses.