Enhanced allergic responses to house dust mite by oral exposure to carbaryl in rats

Epidemiological studies have demonstrated an association between use of carbamate insecticides, including carbaryl, and increased incidence of allergic asthma in farmers. In this study the effect of oral carbaryl exposure on the development of allergic responses to house dust mite (HDM) was examined in female Brown Norway rats. Rats were gavaged for 2 weeks with 0, 2, 10, or 50 mg/kg/day of carbaryl. They were sensitized with a subcutaneous injection of HDM in aluminum hydroxide adjuvant 3 days after the beginning of carbaryl exposure and challenged with antigen via the trachea 1 day after the final carbaryl ingestion. Two days after challenge, antigen-specific cell proliferation in pulmonary lymph nodes was significantly higher in the 50 mg/kg group than in controls, while antigen-specific splenocyte proliferation was decreased in groups dosed with 2, 10, and 50 mg/kg carbaryl. Total protein and lymphocyte number in bronchoalveolar lavage (BAL) fluid were also increased in the 50 mg/kg group. By 7 days after challenge, immune-mediated pulmonary inflammation (eosinophils), antigen-specific immunoglobulin (Ig) E level in serum, and antigen-specific IgE and IgA levels in BAL fluid were significantly elevated in the 50 mg/kg group. No apparent change was observed for lactate dehydrogenase and eosinophil peroxidase in BAL fluid, while the number of BAL macrophages were decreased in groups dosed with 10 and 50 mg/kg carbaryl. The results suggest that carbaryl may cause systemic immune suppression, while enhancing pulmonary allergic responses to house dust mite antigen.