Background: Reports denote that changes in day length enhance or suppress components of immune function in several mammalian species. The aim of present experimental study is
directed to test the hypothesis deals with the effect of photoperiods on some immune limbs responsiveness.
Materials and Methods: Twenty six male and female BALB/C mice, 5-7 weeks old, 14- 18gm weight divided into two groups, test groups (n.=8 mice for each sex) and control
groups (n.=5 for each sex). Test groups were kept in a dark room for a month, while control groups were kept in a room where the photoperiod was day light: darkness 12:12hr. All
studied groups immunized with o.2ml (10% sheep red blood cells) on day 4 and 8 of the last 12 days of the experiment. The weight of all animals were measured at the beginning and the
end of the experiment. Arthus reaction, delayed type hypersensitivity and serum antibody titer were assessed on day 11 and 12 of program.
Results: Significant increased (P<0.005) in body weight, index level of Arthus reaction, delayed type hypersensitivity and serum antibody titer in the test groups in comparison with
the control groups.
Conclusion: Data are consistent with the hypothesis that immune parameters are enhanced in short photoperiods or continuous darkness
