Restoration of immunoregulation in splenic lymphocyte populations of mice fed reduced dietary protein

Abstract

Moderate, acute reduction of dietary protein in young mice often leads to increases in humoral immune responses. To test the hypothesis that reduction of dietary protein affects T lymphocyte regulation of the humoral immune response, in vitro humoral immune responses to sheep erythrocytes (SRBC) and bromelain-treated mouse erythrocytes (BrMRBC), were examined in BDF 1 and BALB/c mice fed diets low in protein (4% or 6% casein) compared with well-fed (20% casein) controls. In addition, the immunoregulatory splenic T lymphocyte subset profile was evaluated in mice fed the 4% and 20% casein diets. Groups of female BDF1 and BALB/c mice 5 weeks of age were fed one of the three diets for 5 weeks. Mice fed the 4% casein diet exhibited less body weight and splenic lymphocyte number than mice from the other two dietary groups. BDF 1 but not BALB/c mice fed the 4% casein diet exhibited significantly increased in vitro and in vivo immune responses to optimal or high doses of SRBC. On the other hand, both BDF 1 and BALB/c mice fed the 4% casein diet exhibited a significantly higher immune response to BrMRBC. The increased response of 4% casein-fed BDF 1 mice was related to an inability to generate adequate specific immunoregulatory T cells involved in suppressing the response. Co-culturing with Lyt1 + or Lyt2 + T cells from well-fed mice regulated downwardly the enhanced autoimmune, anti-BrMRBC response of mice fed the 4% casein diet. Decreased suppressor T lymphocyte activity in BDF 1 mice, but not BALB/c mice fed the 4% casein diet was confirmed by the significant depression of the Lyt2 + suppressor T cell number in the spleen evaluated by direct immunofluorescence using monoclonal antibodies which identify T lymphocyte subsets. These results indicate that moderate, acute reduction of dietary protein in young mice affects the regulatory functions of T cells but not the differentiation of B cells to antibody-forming plasma cells. This effect seems to be dependent upon the strain of mouse used.