Suppression of the murine gut mucosal IgA response to cholera toxin with oral cyclosporine

Abstract

The gut mucosal immune system may be a primary target for many ingested chemicals. Methods have been developed to examine the effects of chemicals on the systemic humoral immune response; however, studies to evaluate various methods of assessing the local gut mucosal immune response in a toxicology assay have been limited. The objectives of this study were to examine the effects of the known immunosuppressive compound, cyclosporine (CYS), on the generation of a cholera toxin (CT)-specific gut mucosal IgA response and evaluate the methods used to measure the gut IgA response. Groups of female B6C3F1 mice were left untreated or were treated daily, p.o., with corn oil (vehicle) or CYS at doses of 10 and 50 mg/kg for 20 days. On Days 3 and 13, mice were sensitized p.o. with CT. On Day 21, mice were terminated, gut washings were collected, and lamina propria lymphocytes were extracted from gut tissue with collagenase treatment. Cholera toxin-specific IgA in the gut washings was measured by an ELISA. The numbers of CT-specific IgA (CT-IgA) and total IgA antibody-forming cells (spotforming cells, SFC) obtained from the lamina propria were determined by the ELISPOT method. A dose of 50 mg/kg CYS produced a significant decrease in the amount of CT-IgA in gut washings. This dose also decreased the number of cells recovered from the lamina propria by at least 50%. The amount of CT-specific SFC/million lamina propria cells decreased with a dose of 10 mg/kg CYS, whereas 50 mg/kg CYS did not alter the response. When the CT-IgA SFC response was calculated on the basis of lamina propria cells obtained per mouse, both the 10 and 50 mg/kg dose were found to suppress the response by at least 50% of control. The amount of IgA-SFC/total lamina propria cells obtained per mouse was also found to be decreased with a dose of 50 mg/kg. Thus, the results indicate that oral exposure to CYS results in a suppressed CT-specific IgA response. In comparing the two endpoints, measurement of CT-specific SFC was a more sensitive indicator. However, collection of gut washings and measurement of CT-IgA by ELISA is much easier than the labor-intensive methods required to isolate lamina propria lymphocytes.