No abstract

In these experiments we examined the genetic control of the secretory IgA (sIgA) response to cholera toxin (CT) after CT feeding. Inbred, congenic and intra-H-2I region recombinant mouse strains were immunized with intragastric application of 10 micrograms CT on days 0 and 14. Samples of intestinal secretions and plasma were collected 1 week after the second dose and antibodies to CT measured in them by antigen- and isotype-specific enzyme-linked immunosorbent assay. In three different sets of H-2-congenic strains the intestinal IgA anti-CT response clearly depended on the H-2 haplotype rather than on background or IgH genes. H-2b (B10, A.BY/SnJ, C3H.SW) and H-2q (B10.T(6R), DBA/1J) strains were high responders, H-2k (B10.BR, C3H/He), H-2s (A.SW/SnJ) and H-2d (B10.D2) strains were low responders. Within the H-2 complex the intestinal IgA anti-CT response was mapped to the I-A subregion with the use of congenic intra-H-2I region recombinant strains: B10.A(3R) and B10.A(5R) were high responders and B10.A(4R), B10.MBR and B10.GD were low responders. Plasma IgG anti-CT after CT feeding paralleled the sIgA results. Surprisingly, the sIgA and plasma IgG anti-CT responses in individual mice of the various strains tested showed a highly significant positive correlation. We conclude that both the sIgA response and plasma IgG anti-CT response after CT feeding is controlled by the I-A subregion of H-2.

No abstract

The feeding of protein antigens to mice results in a state of tolerance when feeding is followed by parenteral immunization. Cholera toxin (CT) is a protein that has been used extensively as a potent oral immunogen for mucosal IgA responses, but CT feeding also stimulates a substantial plasma IgG antibody response. This latter finding prompted us to study whether or not CT induces oral tolerance. Mice were fed 5 mg keyhole limpet hemocyanin (KLH) or 10 micrograms CT at least twice before parenteral immunization with 1 microgram KLH or CT in alum i.p. Plasma and intestinal secretions were collected at intervals. The specific IgG or IgA antibody in the samples was measured by ELISA. Although KLH feeding did induce oral tolerance, CT feeding did not induce oral tolerance in any of three mouse strains tested or at any dose of CT given orally. The feeding of the B subunit of CT did not result in oral tolerance either. When both CT and KLH were fed together, CT was able to abrogate oral tolerance to KLH, an antigenically unrelated protein. Moreover, feeding CT along with KLH stimulated secretory IgA anti-KLH responses, whereas no such IgA responses were found when KLH was given alone. Thus, in these experiments with protein antigens, IgA immunization and oral tolerance were reciprocally linked and did not occur simultaneously. CT appears to abrogate oral tolerance and to stimulate secretory IgA responses by altering the regulatory environment in gut-associated lymphoid tissue, shifting it toward responsiveness.

Cholera toxin (CT) has been found to be an extremely potent immunogen for mucosal IgA responses when administered via the intestine. This study has examined both mucosal and systemic immune responses after feeding CT and compared these responses with those obtained after feeding keyhole limpet hemocyanin (KLH), another protein that is strongly immunogenic in mice. Feeding CT to mice resulted not only in IgA antibody in intestinal secretions but also resulted in substantial plasma IgG and IgA antibody levels. Feeding KLH in much larger quantity resulted in little or no antibody response in intestinal secretions or plasma. Lymphoid cells from various tissues of mice fed CT were cultured in vitro for 10 days and the supernatant was tested for antibody to CT. Spontaneous antibody synthesis (no antigen added to cultures) was present in cultures of each cell type, but IgG anti-CT was found mainly in cultures of spleen and mesenteric lymph node cells and IgA anti-CT mainly in cultures of Peyer's patch and lamina propria cells. Peyer's patch cells cultured with CT as antigen synthesized both IgG and IgA anti-CT, suggesting that the antibody response to both isotypes originated in this site. Helper T cell activity for both IgA and IgG anti-CT was detected in spleens, mesenteric lymph nodes, and Peyer's patches. Lastly, when KLH and CT were fed to mice at the same time, an intestinal IgA anti-KLH and plasma IgG anti-KLH response was stimulated, a response pattern similar to that occurring to CT after CT was fed alone. We conclude that mucosal stimulation by CT generates both a systemic IgG and mucosal IgA response to this antigen, and that CT can cause a similar pattern of response to an unrelated protein antigen when both are administered into the intestine at the same time. The data favor the idea that both the IgG and IgA responses originate in GALT and then disseminate to other tissues. We propose that CT accomplishes these effects by altering the regulatory environment within GALT.