Heavy metal modulation of lymphocyte activities--II. Lead, an in vitro mediator of B-cell activation.

Investigation of the immunopotentiating effect(s) of Pb2+ on the humoral immune response has provided evidence that a heavy metal can alter the proliferation and differentiation of B-cells. Pb2+ interacted with B-cells to enhance both their proliferation and their differentiation into sheep red blood cell (SRBC)-specific PFC. Preincubation of B-cells with Pb2+ for only 1 h enhanced their activities. Enhancement of in vitro humoral immunity to SRBC was due to direct Pb2+ activation of B-cells and enhancement of T-cell help. Furthermore, Pb2+ and the cyclic nucleotides dibutyryl cyclic adenosine monophosphate (DBcAMP) or cyclic guanosine monophosphate (cGMP) worked in a synergistic manner to enhance the B-cell proliferation, and Pb2+ and DBcAMP synergistically enhanced PFC development. Ni2+, which had been shown to enhance PFC development in cultures of spleen cells in a manner equivalent to Pb2+, did not enhance PFC development in B-cell cultures as well as Pb2+ and did not produce synergistic effects with DBcAMP or cGMP. The possible mechanisms by which Pb2+ enhances B-cell activities and the implications of these effects are discussed.