ABSTRACT
Thirty male mature albino rats arranged in three equal groups [A, B and C] were used in this experiment. Prior to the test, group B was subjected to heat [38 degree +/- 2] four hrs. daily for 14 days in their immature life. During the whole experiment, both groups B and C were exposed to heat [38 degree +/- 2] 4 hours daily for 30 days [the time of experiment] while group A was kept under comfortable climate [25 degree +/- 2]. The three groups were injected intravenously in their tail vein with sheep red blood corpuscles at 0 and 21 days of experiment; at 30 days their sera were collected and the anti sheep antibodies were assayed by the tube agglutination method. The antibody titre decreased significantly in both groups compared to control, this decrease was more evident in group B which was exposed to heat during immature life also. This result denoted that heat has an in-vivo immuno-suppressive effect on the murine humoral response, this effect was more pronounced after longer exposure, earlier exposure or both