Activation and proliferation signals in mouse B cells. I. A comparison of the capacity of anti-Ig antibodies or phorbol myristic acetate to activate B cells from CBA/N or normal mice into G1.

B lymphocytes from the CBA/N mouse do not synthesize DNA when cultured with anti-Ig antibodies. However, these cells like normal B cells, do manifest increased Ia antigen expression and RNA synthesis (i.e. enter G1) when stimulated by anti-Ig, even at doses which are nonmitogenic for normal B cells. Pretreatment of both normal and CBA/N B cells with anti-Ig also primes them to give an enhanced proliferative response to lipopolysaccharide (LPS). The tumor promoter phorbol myristic acetate (PMA) also enhances RNA synthesis and Ia antigen expression in B cells from both normal and CBA/N mice. However, PMA only primes CBA/N B cells to respond to LPS: pretreatment of normal B cells with PMA causes a modest suppression of LPS-induced, and a marked suppression of anti-Ig induced, DNA synthesis. These results therefore confirm and extend earlier data showing that there are distinct activating (G0 to G1) vs. proliferative (G1 to S) signals discernible in B cells. They also suggest that the activation mechanism of CBA/N B cells is subtly different from that of any known subpopulation of normal B cells.