Anti-Ig-stimulated B lymphoblasts can be restimulated via their surface Ig

Engaging AgR (surface Ig) on B lymphocytes leads to rapid inositol phosphate turnover and elevation of intracellular [Ca2+]. Continuous receptor occupancy (greater than 18 h) by anti-Ig leads to transit of most B lymphocytes from G0 to G1 stage of the cell cycle (blast transformation); a fraction of cells continue into S phase but do not proliferate continuously in the absence of growth factors. Prolonged exposure to ligand can induce receptor desensitization of some receptors. We therefore investigated whether such desensitization occurs in B cells activated by insolubilized anti-Ig. Resting B cells and anti-Ig-activated blasts were examined for their potential to elevate [Ca2+]i, maintain viability, and synthesize DNA in response to reexposure to anti-Ig. B cells and anti-Ig blasts had similar basal [Ca2+]i levels. Anti-Ig blasts retained the capacity to increase [Ca2+]i in response to anti-Ig; the magnitude of the increase was equal to or greater than that observed with resting B cells and occurred in more than 90% of cells. Isolated anti-Ig blasts subcultured in the presence of T cell-derived growth factors for 3 to 5 days responded to restimulation by anti-Ig with an increase in [Ca2+]i similar to that observed in freshly isolated blasts. The B cell and B lymphoblast ion channels were found to be permeable to Ca2+ but impermeable to Mn2+. Finally, blasts restimulated by anti-Ig retained viability and incorporated low levels of [3H]thymidine for 24 h. These results suggest that AgR on activated B lymphocytes can remain functionally coupled to intracellular signaling pathways and can participate in immune responses subsequent to initial activation.