The effects of the light-dark cycle on humoral and cell-mediated immune responses of mice.

When groups of Balb/c mice were immunized with SRBC, a thymus-dependent antigen, at a time interval of 4 h, the number of PFC in the spleen 4 days after immunization exhibited a marked circadian rhythm with an acrophase at -129 degrees (p less than 0.01), while the hemagglutination titers against SRBC also showed a circadian variation with an acrophase at -121 degrees (p less than 0.01). However, the immune response in C3H/HeN mice against PVP, a thymus-independent antigen, especially serum antibody HA titers, did not show a significant circadian rhythm, and the amplitude of the variation was less than that found in Balb/c mice immunized with SRBC. The cell-mediated immune response, contact hypersensitivity to PC, in mice had a marked circadian rhythm with the timing of the challenge of the antigen (acrophase at -129 degrees). From these data it is suggested that the thymus or thymus-derived lymphocytes may play an important role in the circadian rhythm in both humoral and cell-mediated immune responses.