Differing effects of dietary protein deprivation on the production of rosette-forming cells in the lymph nodes and the spleen and on the levels of serum haemagglutinins in rats immunized to sheep red cells.

After two intraplantar injections of sheep red blood cells (SRBC) + Freund's complete adjuvant given at intervals of a week, rats which had been deprived of dietary proteins for 65 days produced much smaller quantities of serum haemagglutinins than normally fed rats. On the other hand protein-deprived rats reacted with at least the same intensity as the controls with respect to the phenomenon of immunocyto-adherence, tested by counting the rosette-forming cells in the lymph nodes and the spleen. The number of these cells per whole organ remained normal but their proportion per 10 lymphocytes exceeded, by a considerable extent, the value in the control rats. This phenomenon was apparently linked to the predominant reduction in the population of T-lymphocytes, resulting from the atrophy of the thymus that follows deprivation of proteins. Infact in the non-deficient adult rats which had been thymectomized at the age of 25 days, there was also found to be a fall in the level of serum anti-SRBC haemagglutinins, contrasting with an increase in the number of rosette-forming cells per 10 lymphocytes in the lymph nodes and spleen and the presence of a normal or even increased number of these cells per lymphoid organ. It was only when thymectomy and the protein-free diet were combined that a reduction was obtained in the total rosette content of the lymph nodes. Histological and autoradiographic examination of the popliteal lymph nodes showed that protein starvation reduced both the thymus-independent and thymus-dependent zones, but that the cellular proliferation due to the antigenic stimulation involved, in the protein-deprived rats, the B-lymphocytes far more than the T-lymphocytes; this happened to a greater extent if the animals had been thymectomized. It appears that the diminution in the population of T-lymphocytes following either protein-deprivation or late (not neonatal) thymectomy was by itself insufficient to influence the phenomenon of immunocyto-adherence, although there was impairment of the serum haemagglutinin response to SRBC. Only the association of protein deficiency with late thymectomy reduced both of the reactions.