Modulation of stress-induced murine lymphoid tissue involution by age, sex and strain: role of bone marrow.

C57BL/6 and Balb C male and female mice of various ages were stressed by immobilization for 1 h/day (1, 2, 3, 5, 8, 11 or 14 consecutive days). The animals were then killed for determination of total body weight and the weights of the thymus, spleen and axillary lymph nodes. In addition, the total number of cells in the thymus and the proportion of lymphoid cells in the bone marrow cell population was defined. The effects of stress were modulated by age, sex and strain. Stress-induced involution of the thymus was generally more pronounced in older animals, while for the spleen was the opposite. Involution of the thymus was higher in males than in females, but there were no marked differences between the sexes in the response of the spleen. In general C57BL/6 mice were more sensitive to stress than Balb C mice. However, for the involution induced by stress on lymph nodes there were not a clear trend with age, sex or strain. In male and female mice of all ages and both strains, stress led to statistically significant reductions in the absolute number of cells inside the thymus and spleen and in the proportion of lymphoid cells in the bone marrow.