Secretory immunoglobulin A response to Shiga toxin in rabbits: kinetics of the initial mucosal immune response and inhibition of toxicity in vitro and in vivo.

Although the role of Shiga toxin in dysentery is unknown, the toxin is cytotoxic to HeLa cells, causes fluid secretion in rabbit intestine, and is lethal to rabbits and mice when injected parenterally. In the present study, rabbits received three weekly doses of Shiga toxin directly into chronically isolated ileal loops. Within a week, secretions from these loops contained immunoglobulin A (IgA) anti-Shiga toxin. The titer of IgA anti-Shiga toxin increased after weekly doses 2 and 3. Little IgG anti-Shiga toxin was present in loop secretions, although high titers of IgG anti-Shiga toxin were found in the sera. These loop secretions were able to neutralize the cytotoxic effects of Shiga toxin in the HeLa cell assay. The capacity to neutralize the cytotoxicity of the toxin correlated strongly with the IgA anti-Shiga toxin titer in these same secretions. Pooled immune loop secretions were also able to significantly reduce fluid accumulation in acutely ligated loops in rabbits, while loop secretions from control rabbits could not. Shiga toxin elicited a strong secretory IgA response upon application to the intestine. Further, the mucosal antibodies produced functioned to prevent the toxic effects of Shiga toxin both in vitro and in vivo.