Anti-cholera toxin IgA-, IgG- and IgM-secreting cells in various rat lymphoid tissues after repeated intestinal or parenteral immunizations.

Single antibody-secreting spot-forming cells (SFC) of the 3 main isotypes were counted in lymphoid cells from the gut lamina propria (LP), Peyer's patches (PP), mesenteric nodes (MN) and spleen (SP) of rats immunized 2-6 times intraduodenally (ID) or intraperitoneally (IP) with cholera toxin (CT). Responses for all isotypes peaked in all tissues after 4 ID- or IP-immunizations at much larger values than previously reported, and significantly decreased thereafter, except in LP and PP after IP-injections, where IgA- or IgG-SFC, but not IgM-SFC, only appeared or increased after 6 IP-doses. The highest IgA-SFC numbers (17% of tested cells) were in LP after 4 ID-doses. The isotype ratio was IgA greater than IgG greater than IgM in LP and PP after ID-injections, but IgG greater than IgA greater than IgM in MN and SP after both ID- and IP-routes. The isotype dispersion was much larger in LP and PP than in MN and SP. Our data show that at least 4 IP CT-doses were required to only elicit a few IgG- and almost no IgA-SFC in LP and PP, outlining the need for intestinal CT-immunizations to induce strong mucosal IgA-SFC responses. We also show good systemic responses elicited both by enteral and parenteral routes, and the small contribution of PP in total SFC, particularly after parenteral immunizations.