Nutritional factors and autoimmunity. III. Zinc deprivation versus restricted food intake in MRL/1 mice--the distinction between interacting dietary influences.

To investigate further the modulation of autoimmune disease by nutritional means, the influence of zinc deprivation upon the development of the immunopathology of MRL/I mice was studied. Because some effects of zinc deficiency may be due to associated inanition and consequent caloric deprivation, mice with similarly restricted food intake but adequate zinc intake were also studied. Zinc restriction was introduced at either 4 or 10 wk of age and was continued throughout the study. When zinc deficiency was introduced at 4 wk of age, a significant delay in the appearance of the physical findings of MRL/I mice, including open sores, necrotic ears, arthritis, and end-stage cachexia, was noted. In addition, zinc deficiency introduced at this age resulted in a lower incidence and titer of antibodies to dsDNA and less severe glomerulonephritis than control mice. Furthermore, the immune response of zinc-deprived MRL/I mice was better preserved than control animals, and most importantly, survival was significantly prolonged. Pair-fed controls also showed delayed progression of their disease, but animals restricted isocalorically from 4 wk of age experienced a more rapid onset of the lupus-like syndrome than did their zinc-deprived counterparts. In contrast, when zinc deprivation was introduced at 10 wk of age, it had little beneficial effect upon disease progression. Indeed, caloric restriction introduced at this age had a greater impact than did zinc deficiency. Nonetheless, despite the variable influence of zinc deprivation and pair-feeding on autoimmune disease, zinc deprivation, whether introduced at 4 or 10 wk of age, resulted in a significantly greater reduction of lymphoproliferation. Successful modulation of disease activity by nutritional changes will depend on understanding the mechanisms of these differential pathologic processes.