Developmental atrazine exposure suppresses immune function in male, but not female Sprague-Dawley rats.

Each year, 75 million pounds of the broadleaf herbicide atrazine (ATR) are applied to crops in the United States. Despite limited solubility, ATR is common in ground and surface water, making it of regulatory concern. ATR suppresses the immunomodulatory hormones prolactin (PRL) and the thyroid hormones (THs), with developmental exposure to ATR permanently disrupting PRL regulation. We hypothesized that ATR may cause developmental immunotoxicity through its disruption of PRL or THs. To test this hypothesis, pregnant Sprague-Dawley (SD) rats were exposed to 35-mg ATR/kg/d from gestational day (GD) 10 through postnatal day (PND) 23. Separate groups were exposed to bromocryptine (BCR) at 0.2 mg/kg/2x/day to induce hypoprolactinemia or to propylthiouracil (PTU) at 2 mg/kg/day to induce hypothyroidism. After the offspring reached immunologic maturity (at least 7 weeks old), the following immune functions were evaluated: natural killer (NK) cell function; delayed-type hypersensitivity (DTH) responses; phagocytic activity of peritoneal macrophages; and antibody response to sheep erythrocytes (SRBC). ATR decreased the primary antibody and DTH responses in male offspring only. Neither PTU nor BCR caused immunosuppression in any measured variable, although PTU increased phagocytosis by peritoneal macrophages. These results demonstrate that developmental exposure to ATR produced gender-specific changes in immune function in adult rats and suggest that immune changes associated with ATR are not mediated through the suppression of PRL or THs.

Bone marrow stromal-B cell interactions in polycyclic aromatic hydrocarbon-induced pro/pre-B cell apoptosis.

Environmental polycyclic aromatic hydrocarbons (PAH) and related halogenated hydrocarbons are immunotoxic in a variety of systems. In a model system of B lymphopoiesis, PAH exposure rapidly induces apoptosis in CD43- pre-B and CD43+ pro/pre-B cells. Apoptosis induction by 7,12-dimethylbenzo[a]anthracene (DMBA) is dependent upon AhR+ bone marrow stromal cells and likely involves DMBA metabolism within the stromal cell. However, it is not known if PAH-treated stromal cells release free metabolites or soluble factors that may directly induce B cell death or if the effector death signal is delivered by stromal cell-B cell contact. Here, we demonstrate that supernatants from DMBA-treated bone marrow stromal cells contain an activity capable of inducing apoptosis in pro/pre-B cells cocultured with stromal cells. This activity (1) is not produced when stromal cells are cotreated with DMBA and alpha-naphthoflavone (alpha-NF), an aryl hydrocarbon receptor (AhR) and cytochrome P-450 inhibitor, (2) is > or = 50 kDa, (3) is trypsin and heat sensitive, and (4) is dependent on AhR+ stromal cells, which in turn deliver the effector death signal to pro/pre-B cells. The results (1) argue against a role for a soluble, stromal cell-derived cytokine as the effector of PAH-induced pro/pre-B cell death, (2) exclude the possibility of a free metabolite acting directly on AhR- pro/pre-B cell targets, and (3) suggest the elaboration by stromal cells of a relatively stable, DMBA metabolite-protein complex capable of acting on other stromal cells at some distance. Collectively, these studies suggest that, while stromal cell products, e.g., metabolite-protein complexes, may affect the function of distant stromal cells, the effector death signal delivered by stromal cells to bone marrow B cells is mediated by cell-cell contact.