Interleukin 4 reduces expression of inhibitory receptors on B cells and abolishes CD22 and FcγRII-mediated B cell suppression

Inhibitory receptors CD22, FcgammaRII (CD32), CD72, and paired immunoglobulin-like receptor (PIR)-B are critically involved in negatively regulating the B cell immune response and in preventing autoimmunity. Here we show that interleukin 4 (IL-4) reduces expression of all four on activated B cells at the level of messenger RNA and protein. This reduced expression is dependent on continuous exposure to IL-4 and is mediated through Stat6. Coligation of FcgammaRII to the B cell receptor (BCR) via intact IgG increases the B cell activation threshold and suppresses antigen presentation. IL-4 completely abolishes these negative regulatory effects of FcgammaRII. CD22 coligation with the BCR also suppresses activation - this suppression too is abolished by IL-4. Thus, IL-4 is likely to enhance the B cell immune response by releasing B cells from inhibitory receptor suppression. By this coordinate reduction in expression of inhibitory receptors, and release from CD22 and FcgammaRII-mediated inhibition, IL-4 is likely to play a role in T cell help of B cells and the development of T helper cell type 2 responses. Conversely, B cell activation in the absence of IL-4 would be more difficult to achieve, contributing to the maintenance of B cell tolerance in the absence of T cell help.