Effects of Aging upon the Expression of Differentiation and Class II MHC Antigens on the Surface of T Lymphocytes from Normal Human Subjects

This study documents differences in the expression of differentiation antigens and Class II MHC encoded antigens on the T and B cells of young, adult, and older healthy humans as measured by their density on the cell surface. Marker densities were calculated by fluorescence intensity vector analysis, using two-color flow cytometry. Relative changes in marker densities with increasing age were calculated by expressing younger group marker density values as 100%. The following statistically significant changes were observed with advancing age: (1) Increased density of HLA-DR markers on CD3+ and CD8+ cells and CD4 markers in the "adult" group (ages >34 ⩽59 years) (1.5-fold, 0.5-fold, and 0.4-fold increases, respectively) when compared with the "young" group (ages ⩽34 years); (2) decreased density of HLA-DR markers on CD3+ and CD8+ cells and CD8 markers in the "older" group (ages ⩾60 years) (0.2-fold, 0.5-fold, and 0.4-fold decreases, respectively) when compared with the adult group. However, when the "older" group was compared to the young group, the density of HLA-DR markers on CD3 cells and the density of CD4 markers and CD8CD57 markers were significantly higher (1-fold, 0.4-fold, and 0.8-fold) and the CD8 markers were lower (0.4-fold). The size score of individual T cell subsets, as measured by forward light scatter, was uniformly smaller in the older age group when compared with the young group (29.5 ± 4.0% SD); it was also smaller than in the adult group (16.5 ± 2.7% SD). These observations may be of relevance to the decreased level of host immunulogic responsiveness observed with increasing age.