ENHANCED ALLERGIC RESPONSES TO HOUSE-DUST MITE BY ORAL-EXPOSURE TO CARBARYL IN RATS

Epidemiological studies have demonstrated an association between use o f carbamate insecticides, including carbaryl, and increased incidence of allergic asthma in farmers. In this study the effect of oral carbar yl exposure on the development of allergic responses to house dust mit e (HDM) was examined in female Brown Norway rats. Rats were gavaged fo r 2 weeks with 0, 2, 10, or 50 mg/kg/day of carbaryl. They were sensit ized with a subcutaneous injection of HDM in aluminum hydroxide adjuva nt 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 pulmonar y lymph nodes was significantly higher in the 50 mg/kg group than in c ontrols, 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 incr eased in the 50 mg/kg group. By 7 days after challenge, immune-mediate d pulmonary inflammation (eosinophils), antigen-specific immunoglobuli n (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 peroxidas e 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 c arbaryl may cause systemic immune suppression, while enhancing pulmona ry allergic responses to house dust mite antigen, (C) 1998 Society of Toxicology.