Two signals are involved in polyclonal B cell stimulation by T helper type 2 cells: a role for LFA-1 molecules and interleukin 4.

T helper cell type 2 (Th2) cells when triggered by antibodies to CD3 acquire the capacity to stimulate the polyclonal proliferation of syngeneic, resting B cells. Here, we tested the ability of various monoclonal antibodies (mAb) to block the B cell proliferation-inducing potential of such activated Th2 cells. We demonstrate that anti-interleukin 4, as well as anti-LFA-1 antibodies interfere with the T-B cell interaction. In kinetic studies, anti-LFA-1 was found to be operative during the first half and anti-interleukin 4 during the second half of the 48-h culture period. This defines at least two different steps in B cell triggering by Th2 cells. In addition, the data imply that the T-B cell interaction involves an additional structure, namely an activation molecule, on the T cell surface.