EFFECTS OF STRESS ON IMMUNE CELL DISTRIBUTION - DYNAMICS AND HORMONALMECHANISMS

Immune cell trafficking is crucial to the performance of the surveilla nce as well as effector functions of the immune system. Because immune cells travel between tissues through the bloodstream, the numbers and proportions of leukocytes in the circulation provide an important rep resentation of the state of leukocyte distribution in the body. The st udies described here examine significant and selective changes in numb ers and percentages of peripheral blood leukocyte subpopulations in th e rat. These changes were rapidly induced under conditions of mild acu te stress. Stress-induced increases in plasma corticosterone were acco mpanied by a significant decrease in numbers and percentages of lympho cytes, and by an increase in numbers and percentages of neutrophils. F low cytometric analysis revealed that B cell, NK cell, and monocyte nu mbers showed a greater stress-induced decrease than did T cells. All s tress-induced changes were observed during the light (inactive) as wel l as the dark (active) period of the animal's diurnal cycle. Important ly, the stress-induced changes in leukocyte numbers and percentages we re rapidly reversed upon the cessation of stress. Furthermore, the eff ects of stress were largely dependent on adrenal hormones, because the magnitude of the stress-induced changes was significantly reduced in adrenalectomized animals. Moreover, administration of corticosterone t o adrenalectomized animals resulted in a close replication of stress-i nduced changes observed in adrenal-intact animals. These results sugge st that endocrine factors released during stress modulate leukocyte tr afficking and result in the redistribution of leukocytes between the b lood and other immune compartments. Such a redistribution may signific antly affect the ability of the immune system to respond to potential or ongoing immune challenge.