Ig-independent Ig beta expression on the surface of B lymphocytes after B cell receptor aggregation

In order for humoral immune responses to develop, B cells must be able to recognize, bind, and internalize Ags. These functions are performed by the BCR, which is also responsible for initiating and transducing activation signals necessary for B cell proliferation and differentiation. We have examined surface expression patterns of individual components of the BCR following anti-Ig- and Ag-induced aggregation. Specifically, the localization and expression levels of the Ag-binding component, surface Ig (sIg), and the Igbeta component of the Igalpha/Igbeta signaling unit were investigated to determine their individual participation in the internalization and signal transduction. Using primary murine B cells, we found that while >95% of the sIg is internalized following anti-Ig-induced aggregation, 20-30% of Igbeta remains on the surface. These results suggest that sIg and Igbeta may function independently following the initial stages of signal transduction.