Sex-related immune changes in young mice

Here we describe changes in selected immune parameters related to age and s ex in young mice. We focused on the T cell compartment and studied thymuses and spleens from mice 3 to 9 weeks of age in order to bracket the time per iod around murine puberty. With regard to distribution of immune cells, no significant sex-related changes were seen in thymocyte expression of CD3, C D4, CD8, or CD4/CD8 or splenocyte expression of CD3, CD4, CD8, or CD45R/B22 0, a pan B cell marker. For splenocytes, significantly more cells were posi tive for CD3 in older (6-9 week old) compared with younger (3-4 week old) m ice. Splenocyte and thymocyte cell proliferation as measured by DNA synthes is in response to in vitro mitogens was compared for cells from male and fe male mice over the ages studied. Thymocyte proliferation was not related to age or sex of the mice. For splenocytes of the youngest mice (3 weeks old) , the response ts a cell surface-receptor-independent mitogenic combination of phorbol ester and ionomycin induced a significantly greater response in cells from female mice compared with male mice. This trend was reversed fo r mice of 4-6 weeks of age, where the response by splenocytes from males wa s significantly greater than that by cells from females. For mice 7-8 weeks of age, splenocytes from female mice responded significantly less to stimu lation by antibody to CD3, a component of the T-cell receptor. Our results demonstrate that depending on the assays employed, sexual dimorphism in the immune system may be demonstrated prior to puberty.