Surface Immunoglobulin and Fc Receptors on Murine B Lymphocytes: Loss of Receptor Interaction after Cell Activation

Although surface immunoglobulin (sIg) and Fc receptors (FcR) are independent receptors in the membrane of B lymphocytes and are assumed not to interact under normal conditions, it has been shown that anti-Ig-induced redistribution, i.e., patching and capping, of sIg results in the co-capping of FcR, suggesting some type of receptor interaction. We have investigated this phenomenon by comparing the interaction of these receptors on normal vs activated B cells under a variety of conditions. It was found that, in contrast to unstimulated control cells, sIg and Fc receptors on blast cells induced by either Fab′2 anti-Ig or endotoxin protein do not interact, i.e., little if any co-capping was seen. This loss of receptor interaction was not due to increased cell size since cells which were stripped of their sIg and FcR and allowed to re-express both receptors for 24 hr, but which had not increased in size during this period, also failed to show co-capping behavior. Additional experiments showed that the Fc receptors on activated B cells could be capped directly by using complexes of FITC-KLH-anti-KLH, indicating that the loss of sIg-FcR co-capping on activated cells is not due to any restriction in the mobility of the Fc receptor in the membrane. These results strongly suggest that B lymphocyte activation is accompanied by membrane alterations that result in the loss of sIg and FcR interaction and that these changes do not require receptor redistribution and re-expression.