Effect of reduced dietary protein intake on regulation of murine in vitro polyclonal T lymphocyte mitogenesis

Moderate reduction of dietary protein in mice often results in increased cell mediated immune responses. Since alterations in immunoregulation can affect the net immune response, regulation of polyclonal T cell mitogenesis was examined in BALB/c mice fed diets low in protein compared to well-fed controls. Female BALB/c mice, 5 weeks of age, were fed 20% casein, 4% casein or 2% casein diets for 5 weeks. Mice fed the low protein diets exhibited less body weight, and lower splenic lymphocyte number compared to well-fed controls. Nevertheless, 5×10⁵ lymphocytes from mice fed the 4% casein diet responded significantly better to the polyclonal T cell mitogens phytohemagglutin and concanval in A than lymphocytes from control mice. The increased polyclonal T cell mitogenesis in 4% casein fed mice was accompanied by an increased ability to generate suppressor T cells, altered levels of soluble immunoregulatory factors, and increased levels of spontaneously generated prostaglandin E. These results may help explain why mice fed low levels of dietary protein experienced both decreased resistance to infection and increased polyclonal immune responsiveness.