We first studied the effect of dietary protein concentration on immune responsiveness of C57BL/6 mice by measuring the proliferation response of splenocytes to mitogens. We used egg protein (PEP) as a protein source in diet, since PEP contains essential amino acids in good balance. The response of splenocytes to LPS, which is a B-cell specific mitogen, in mice fed on 2% protein diet was significantly lower than those in mice fed on each of 5% or 10% protein diet. While, the response of splenocytes to Con A, which is a T-cell specific mitogen, was unaffected by dietary protein restriction.
Next, we studied the effect of dietary protein type on immune responsiveness in relation to its sulfur amino acid concentration. The response of splenocytes to Con A in mice fed on 10% lactalbumin diet was significantly lower than those of mice fed on each of 10% soy protein (SPI), gluten, casein or PEP diet. The response to Con A of splenocytes in SPI and gluten diet groups were also slightly lower than those of casein and PEP diet groups. However, the response of splenocytes to LPS was unchanged by dietary protein type. In addition, the response of splenpcytes to Con A in SPI diet gruop was significantly increased by the supplement with L-methionine in the diet, which is a first limiting amino acid of SPI and casein. The response of splenocytes to Con A in casein diet group was・ also marginally increased, while, that of gluten diet group did not changed by L-methionine supplement. These results suggest that the immune response in T-cell may be in part controlled by the availability of sulfur amino acid from diet. However, the reason why the splenocytes in lactalbumin diet group shows low resposibility to Con A is uncertain.
