Age-Related Changes of Cytokine Production by Murine Helper T Cell Subpopulations

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Abstract
Mouse CD4+ T cells were subdivided into two subsets by cell surface markers: CD44loCD45RBhi (naive) and CD44hiCD45RBlo (memory) T cells. We have reported that CD44loCD45RBhi T cells, which are predominant in young mice, decreased with age, while CD44hiCD45RBlo T cells increased. Among T cells of the same phenotype, however, it remains to be solved whether or not there is a functional difference between young and old. Therefore, we compared old with young T cells by a cytokine production assay (IL-2, IFN-γ, IL·4 and IL-10). We employed the negative selection method by cell affinity column instead of flow cytometry as it was important to use T cells not reacted with antibodies in the cytokine production assay and as the method is quick enough to preserve the viability of the cells. Then the divided T cells were stimulated with immobilized anti-CD3Ε monoclonal antibody (mAb). Young CD4+ T cells produced more IL·2 and IL·4 than aged CD4+ T cells, while aged CD4+ T cells produced more IL-10 than young cells. There was no distinct age-related change in IFN-γ production. As concerns purified CD4+ T cell subpopulations, young CD44loCD45RBhi T cells produced more IL-2 (5.3-fold higher) than young CD44hiCD45RBlo T cells and much more IL-2 ( >10-fold higher) than both groups of aged T cells. Dramatic IFN-γ production was found in young and old CD44hiCD45RBlo T cells and young CD44loCD45RBhi T cells; however, IFN-γ production of old CD44loCD45RBhi T cells was much lower (1/16-1/20) than that of other cell groups. IL-4 production was mainly observed in the CD44hiCD45RBlo T cell group in both young and old mice, although the former produced more IL-4 (5.2-fold higher) than the latter. There was no remarkable difference between young and old mice in the pattern of IL-10 production. These phenomena could reveal functional heterogeneity of aged CD4+ T cell subpopulations under natural conditions. Even if the surface marker is the same, the pattern of cytokine production is different between young and old cells.

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