Selective effects of cholera toxin on the activation of mouse B cells by different polyclonal activators.

Murine B cells were stimulated in vitro with anti-immunoglobulin (Ig) antibodies, lipopolysaccharide, or with various combinations of phorbol dibutyrate and ionomycin. Very low concentrations (ca. 10(-14) M) of cholera toxin inhibited anti-Ig-stimulated DNA synthesis, while the response to LPS was only abrogated by 2 X 10(4)-10(5)-fold greater concentrations of the toxin. Earlier responses in anti-Ig-stimulated B cells, such as increases in Ia antigen levels, were not affected by the toxin. Protein kinase C-activating phorbol esters, together with Ca2+ ionophores, are believed to stimulate DNA synthesis in lymphocytes by mimicking the two second messengers resulting from ligation of the antigen receptors. However, concentrations of cholera toxin which totally abolish anti-Ig-induced B cell proliferation significantly enhanced DNA and RNA synthesis induced by phorbol dibutyrate plus ionomycin. The results are discussed in terms of possible effects of cholera toxin on guanine nucleotide-binding (G) proteins controlling receptor coupling to second messenger-generating systems in B cells.