Rabbit lymphocytes with receptors for IgM. I. The development of receptors on lymphocytes following intravenous injection of antigen.

Under conditions optimal for detection of receptors for IgM (RFcμ) on human lymphocytes, RFcμ⁺ lymphocytes were not found in any of the tissues of nonimmune rabbits. However, 1 day after iv immunization with alum-precipitated keyhole limpet hemocyanin (KLH) or polymerized human IgG (pol-Ig), rabbit peripheral blood (PB) and spleen (S) demonstrated a significant percentage of lymphocytes (10%) with RFcμ. At 3 days after immunization there was a further increase in RFcμ⁺ lymphocytes (10–13%). By 6 days, however, the percentage of lymphocytes bearing receptors for IgM had returned nearly to zero. Pronase treatment was found to increase expression of RFcμ at 1 and 3 days in pol-Ig-primed tissues (up to 25%) but not in KLH-primed tissues. The percentage of RFcμ⁺ lymphocytes in tissues remained low at 6 days even after Pronase treatment. This time sequence of development of RFcμ⁺ cells after immunization seems interesting in the light of the findings of others that human lymphocytes with receptors for IgM are responsible for help in the PWM-induced differentiation of B cells to plasma cells.