Lead, a major environmental pollutant, is immunomodulatory by its differential effects on CD4+ T cells subsets

Studies were undertaken to address the necessity of B-T cell contact for the enhancement of B cell differentiation caused by the heavy metal lead (Pb). Membrane segregated cultures were used so that the influences of direct B-T cell contact and T cell factors on B cell differentiation could be independently evaluated. B-T cell contact was not absolutely required for Pb's enhancement of B cell maturation to antibody forming cells (AFCs); however, enhancement of the AFC response by Pb was optimal when B-T cell interactions were allowed. These results were corroborated by use of anti-L3T4 (mouse CD4) to block CD4+ T cell-B cell interaction. Blockade of B-T cell contact with anti-L3T4 did not inhibit the enhancement of the AFC response by Pb. Additional experimentation showed that Pb enhanced the AFC response and Ig production in the presence of antigen-specific T cell help, suggesting that Pb enhances B cell differentiation by augmenting cognate help rather than by inducing a response to Pb-altered-self. In studies employing antigen-specific T cell clones, Pb was found to differentially modulate antigen presentation to TH1 versus TH2 T cell clones, in that TH1 activation was inhibited and TH2 activation was enhanced by Pb.