Protein malnutrition reduces the IgA immune response to oral antigen by altering B-cell and suppressor T-cell functions.

Mice fed a protein-deficient diet containing 2% ovalbumin for 6 weeks (PD) show a reduced spleen IgA plaque-forming cell (PFC) response after oral immunization with sheep red blood cells (SRBC), compared to the response of mice fed a control diet containing 20% ovalbumin (C). This reduced IgA PFC response was partially restored by reconstituting the PD mice with an i.v. injection of 5 X 10(5) Peyer's patch (PP) cells from C mice prior to immunization. Reconstitution with B-cell enriched PP, but not helper T-cell (Th) enriched PP, from C mice resulted in an equally elevated IgA response, suggesting that malnutrition induced alterations in the PP B cells yet allowed partially functional Th cells. Reconstitution of PD mice with 1 X 10(7) PP cells from C mice yielded a very low IgA PFC response. This suppression was relieved by removal of Lyt-2+ T cells from the control PP cells prior to transfer. Transfer of spleen, but not PP, cells from oral-immunized PD donor mice to C mice prior to oral immunization resulted in a suppressed IgA PFC response of the recipient mice that was not seen when immune C cells were transferred. Removal of Lyt-2+ cells from the PD spleen cells prior to transfer abolished this suppression. These results suggest that protein deprivation is accompanied by the stimulation of Lyt-2+ suppressor T cells that suppress the IgA response after oral immunization.