Thymus derived (T) lymphocyte subsets restore the immune responsiveness of Peyer's patch lymphocytes from mice fed a diet reduced in protein

The principal immunoglobulin (Ig) that inhibits absorption of intact dietary protein and microbial colonization of the small intestine is secretory IgA produced by lamina propria plasma cells terminally differentiated from B lymphocytes of the Peyer's patches (PP). To determine the effect of reduced dietary protein upon the ability of PP lymphocytes to differentiate into IgA-secreting plasma cells, weanling female BDF mice were fed either a 20% casein (20C) or a 4% casein (4C) diet for 5 to 6 weeks. Mice were then orally primed with sheep erythrocytes (SRBC) four times during a 2-week period to initiate differentiation of PP lymphocytes to anti-SRBC IgA production. Both the PP and splenic lymphocytes of primed mice were incubated with SRBC in vitro to evaluate the capacity to terminally differentiate to anti-SRBC IgA- and IgM-secreting plasma cells upon antigenic stimulation. The in vitro IgA and IgM anti-SRBC immune response of PP lymphocytes from mice fed 4C was significantly lower than the immune response of PP from 20C-fed mice. In contrast, splenic IgM and IgA in vitro immune responses to SRBC of orally primed 4C-fed mice were higher than the response of 20C-fed mice. Addition of Lyt1⁺ T lymphocytes from SRBC-primed donor mice or Interleukin 2 (IL2) to the in vitro PP lymphocyte cultures partially restored the anti-SRBC IgA and IgM immune responses of mice fed 4C. These results strongly suggest that mice fed a diet low in protein possess a PP T-lymphocyte populations that is unable to support a local IgA or IgM immune response, while at the same time possessing a splenic lymphocyte population that has increased capability to mount a systemic IgA and IgM immune response.