Deleterious effects of environmental toxicants such as mercury affect the poor and minorities first and most dramatically. Mercury levels in the environment have been rising 2-5 fold over the last century and 1.5% per year since 1970. Environmental Protection Agency (EPA) lists mercury as a hazardous air pollutant under Title Ill of the federal Clean Air Act. The main goal of the proposed five year project is to further delineate the molecular mechanisms involved in mercury-induced immunotoxicity. Exposure to mercury even at low levels may cause subtle immune system alterations which may indirectly affect ability to resist microbial infections or development of cancers. Mercury may have a devastating effect on the immune system of the neonatal child, but this aspect has not been well studied. Previous studies have shown that mercury may induce autoimmunity, especially in Brown-Norway (BN) rats or in some cases immunosuppression. In the proposed project, we will study the effects of methylmercury chloride (CH3HgCI) using both BN and Sprague-Dawley (SD) rats. We will also study the effects of CH3HgCI on the neonatal immune system in weanling pups by exposing pregnant and lactating rats of both BN and SD strains. Using DNA microarray technology, we will study the changes in cytokine gene expression in lymphoid cells exposed to CH3HgCI in vitro or in vivo as compared to control cells. Based on the results, we will study in-depth, the status of some important Th1 and Th2 cytokines. We will employ both realtime quantitative RT-PCR, ribonuclease protection assay (RPA) and ELISA. These different assays targeting the Th1/Th2 cell responses are expected to give us detailed information on the expression of the cytokines at the level of both transcription and protein production. We will study the control and mercury-exposed immune cells of adult and neonatal rats for activation markers, CD25 (IL-2R alpha) and MHC class II antigens and serum samples for antinuclear antibody, C-reactive protein and circulating immune complexes. To study whether mercury-induced alterations of the immune responses adversely affect host disease resistance mechanisms in vivo, we will experimentally infect the weanling rats with Pseudomonas aeruginosa and study the morbidity and mortality. Comparison of the data obtained using adult and neonatal BN rats which are susceptible to mercury-induced autoimmune-like disease with that of SD rats and correlation of cytokine profiles with the expression of markers for activation and autoimmune disease as well as resistance to infection, will help us further delineate the molecular mechanisms involved in mercury-induced immunotoxicity.