EVALUATION OF THE HUMORAL IMMUNE-RESPONSE OF CD RATS FOLLOWING A 2-WEEK EXPOSURE TO THE PESTICIDE CARBARYL BY THE ORAL, DERMAL, OR INHALATION ROUTES

The objective of this study was to examine the immunotoxicological eff ects of the methylcarbamate pesticide carbaryl via the oral, dermal, o r inhalation routes. Male CD rats were exposed to carbaryl 5 d/wk for a 2-wk period. During nose-only inhalation exposures, rats received ei ther 36, 137, or 335 mg/m(3) carbaryl in acetone for 6 h. Air only and acetone/air controls were run concurrently. Orally exposed animals re ceived either 1 ml corn oil or 10, 25, or 50 mg/kg carbaryl, while der mally exposed animals received either 2 ml acetone or 100, 500, or 100 0 mg/kg carbaryl on their dorsal flank for 6 h. Four days prior to sac rifice, animals from all exposure groups were injected iv with 2 x 10( 8) sheep red blood cells (SRBC). The primary immunoglobulin M (IgM) hu moral immune response to SRBC was then assessed by measuring SRBC-spec ific antibody-forming cells (AFC) and levels of serum anti-SRBC IgM an tibody, respectively, using the hemolytic plaque assay and an enzyme-l inked immunosorbent assay. Individual body weights, spleen, thymus, an d liver weights, spleen cell number, and red and white blood cell (RBC , WBC) counts were obtained for each animal. Following nose-only inhal ation exposures, dose-dependent decreases in thymus weights, spleen ce ll number, AFC/spleen, AFC/10(6) splenocytes, and serum levels of SRBC -specific IgM antibody were observed. Significant decreases of 33, 57, and 22% in spleen cell number, AFC/spleen, and thymus weight, respect ively, were found at the 335 mg/m(3) exposure level. Animals exposed o rally to 25 mg/kg carbaryl had a 34% decrease in WBC counts. A 34% dec rease in WBC and a 13% increase in RBC counts were observed at the 50 mg/kg oral dose. Significant decreases in liver weights ranging from 1 1 to 13% were found at all oral exposure levels. Dermal exposure to ca rbaryl revealed no significant toxicological effects. Results indicate that humoral immune suppression was observed following inhalation, bu t not following oral or dermal exposures to carbaryl. Immunotoxicologi cal studies evaluating pesticides need to consider relevant exposure r outes and dosages for appropriate risk assessment procedures and expos ure limits to be established.