Strain polymorphism in progression of aging: changes in CD4, CD8 bearing subpopulations.

Polymorphism of age-related changes in CD4 (L3T4) and CD8 (Lyt-2) determinants of spleen and thymus cells was assessed by fluorescence-activated flow cytometry. Cells from mice ranging from 5 weeks to greater than 2 years of age were examined. There is little age-related change in the proportion of CD4+ CD8- splenocytes in A, C57BL/6, DBA/1, DBA/2, and SJL mice (slopes 0.04, 0.06, 0.08, 0.17 and 0.17, respectively, when age in weeks was plotted against % of positive cells). Changes in the composition of the thymus are much more profound: CD4+ CD8+ cells of SJL mice decrease from 70% to less than 10% as the animals age from 5 to 69 weeks (slope -1.03), and in DBA/2 mice from 5 to 110 weeks (slope -0.88). While this decrease in CD4+ CD8+ cells occurs, there is a compensatory increase in CD4+ CD8- and CD4- CD8+ cells; this is a shift in the relative proportion of subpopulations rather than an increase in absolute cell numbers of a particular subpopulation. In contrast to the age-related changes of SJL and DBA/2 mice, there is relatively little change in the proportion of CD4+ CD8+ thymus cells in mice of strains C57BL/6, DBA/1 and A (slopes -0.03, -0.14 and -0.15, respectively).