Lead effects on development and function of bone marrow-derived dendritic cells promote Th2 immune responses

Although lead (Ph) has significant effects on the development and function of macrophages, B cells, and T cells and has been suggested to promote allergic asthma in mice and humans, Ph modulation of bone marrow (BM)-derived dendritic cells (DCs) and the resultant DC effects on Th1 and Th2 development have not been examined. Accordingly, we cultured BM cells with murine granulocyte macrophage-colony stimulating factor (mGM-CSF) +/- PbCl2. At day 10, culture supernatant (SN) and non-adherent cells were harvested for analysis. Additionally, day 10 nonadherent BM-DCs were harvested and recultured with mGM-CSF+LPS +/- Pb for 2 days. The day 10 Ph exposure significantly inhibited BM-DC generation, based on CD I I c expression. Although fewer DCs were generated with Ph, the existing Pb-exposed DCs had significantly greater MHC-II expression than did the non-Pb-exposed DCs. However, these differences diminished upon LPS stimulation. After LPS stimulation, CD80, CD86, CD40, CD54, and MHC-II were all up-regulated on both Pb-DCs and DCs, but Pb-DCs expressed significantly less CD80 than did DCs. The CD86:CD80 ratio suggests a Pb-DC potential for Th2 cell development. After LPS stimulation, IL-6, IL-10, IL-12 (p70), and TNF-alpha levels significantly increased with both Pb-DCs and DCs, but Pb-DCs produced significantly less cytokines than did DCs, except for IL- 10, which further supports Pb-DC preferential skewing toward type-2 immunity. In vitro studies confirm that Pb-DCs have the ability to polarize antigenspecific T cells to Th2 cells. Pb-DCs also enhanced allogeneic and autologous T cell proliferation in vitro, and in vivo studies suggested that PbDCs inhibited Th1 effects on Immoral and cell-mediated immunity. The Ph effect was mainly on DCs, rather than on T cells, and Pb's modification of DC function appears to be the main cause of ph's promotion of type-2-related immunity, which may relate to Ph's enhanced activation of the Erk/MAP kinase pathway. (c) 2007 Elsevier Inc. All rights reserved.