Priming and suppression of the intestinal immune response to cholera toxoid/toxin by parenteral toxoid in rats.

Parenteral immunization of rats with cholera toxoid had both priming and suppressive effects upon the antitoxin response in jejunal lamina propria to locally applied toxoid/toxin. Priming was detected when parenteral toxoid was given i.p. but not i.v. or s.c., was enhanced by Freund's adjuvant, and appeared to reflect enhanced encounter of i.p. antigen with IgA-committed lymphocytes in extra-intestinal mucosa-associated lymphoid tissue. In contrast, suppression followed parenteral toxoid given i.p., i.v., or s.c.; suppression was antigen specific and lasted at least 16 weeks. Parenteral toxoid suppressed both primary and secondary types of mucosal antitoxin responses, ultimately preventing the generation of antitoxin-containing immunoblasts from Peyer's patches. Since suppression followed parenteral immunization by routes that did not provoke mucosal priming, it was, at least in those instances, not simply a regulatory consequence of mucosal priming. These results support the notion that priming and suppression of a specific mucosal immune response are independent effects of parenteral immunization that are probably determined by the distribution of antigen to mucosa-associated and systemic lymphoid tissue, respectively.