Effects of a protein-free diet on the changes in cyclic AMP and cyclic GMP levels induced by immunization in splenic T and B lymphocytes in the rat.

The levels of cyclic nucleotides, cAMP and cGMP, were determined in splenic lymphocytes of normally fed (N) and protein deprived (PD) rats before and at different time intervals after a single injection of sheep erythrocytes. Assays were performed with protein binding methods on unseparated as well as on T and B cells fractionated by filtration through nylon wool. The cAMP levels increased in unfractionated cells and in T and B lymphocytes 2 hours following immunization of N rats. Another rise in cAMP levels occurred after 3 days in B lymphocytes, but there was also a simultaneous increase of the cGMP levels in preparations of unfractionated cells and in B lymphocytes. The PD diet suppressed or delayed most of the aforementioned changes. Thus, the immunodepressive effect of such a diet may be ascribed to the inhibition of both the early signal (increase of cAMP levels and of cAMP/cGMP ratio) leading to T and B differentiation and the later signal (increase of cGMP levels) which initiates antibody production.