| Abstract: | The influence of a phase shift in the light-dark cycle on humoral immune responses against sheep red blood cells (SRBC), a thymus-dependent antigen, and against polyvinylpyrrolidone (PVP), a thymus-independent antigen, was studied by using 180 BALB/c mice and 150 C3H/HeN mice. Significant suppression of the immune response to SRBC and the number of splenic plaque-forming cells (PFC) and hemagglutination (HA) titers was observed on days 5 and 6 after inversion of the light-dark cycle. On the other hand, the number of splenic PFC and HA titers in the blood against PVP were minimally suppressed by the phase shift in C3H/HeN mice, except for distortion of the rhythmicity. Corticosterone levels in the blood on days 5 and 6 after inversion were higher than those under a normal lighting regimen. The appearance of the high corticosterone level in the blood after the inversion almost concurred with the suppression of the immune response to SRBC. A decrease of the proportion of splenic T cells was also observed on day 6 after the inversion. These results show that a phase shift in the light-dark cycle provokes suppression of the immune response to SRBC, possibly through an increase of secretion of corticosterone after light-dark inversion, which induces a decrease of the proportion of T lymphocytes in the spleen. |
