Synergistic stimulation of human B lymphocytes by anti-CD40 monoclonal antibodies and synthetic lipopeptide analogues from Escherichia coli lipoprotein.

Human tonsillar B lymphocytes were stimulated with synthetic lipopeptide analogues of Escherichia coli lipoprotein alone or together with anti-CD40 and/or interleukin-4 (IL-4). While lipopeptides alone or lipopeptides plus IL-4 did not include proliferation of B lymphocytes, synergistic stimulation was observed when anti-CD40 antibodies were added. Proliferation was even more pronounced in the presence of Fc receptor type II (FcRII)-transfected L cells. Compared to the stimulus anti-CD40 plus IL-4 plus FcRII-transfected fibroblasts exerted, the addition of lipopeptides induced a more rapid maximal response which peaked on day 4. Antibody production could also be enhanced by lipopeptides. Our data provide evidence that lipopeptides, which act as mitogens toward murine B lymphocytes, also stimulate human B lymphocytes, provided that co-signals are added.