Influences of nutrition on immunity and susceptibility to mouse hepatitis virus type 2

Resistance to mouse hepatitis virus (MHV) in C3H mice is a genetic trait which appears 3-4 weeks after birth. However, when these animals were weaned on a low protein diet (8% casein), they remained susceptible to MHV-2 infection until they reached 8-9 weeks of age. During this period, the protein-restricted C3H mice were as susceptible to MHV-2 as the genetically susceptible congenic C3Hss strain. The delay in the emergence of resistance in the protein-restricted mice could be corrected by injecting these animals with spleen cells from 6-week-old C3H mice. Thymocytes from normal C3H mice, and splenocytes and thymocytes from protein-restricted C3H mice, were not protective. However, spleen cells from the protein-restricted mice were more responsive to phytohaemagglutinin, lipopolysaccharide and concanavalin A than spleen cells from normal C3H. The enhanced lymphoproliferative response in spleen cells from protein-restricted mice was abrogated by the addition of plastic-adherent cells obtained from normal C3H spleens. Spleen cells from protein-restricted and from genetically susceptible C3Hss mice also possessed more spontaneous cytotoxicity against MHV-infected 3T3 fibroblasts.