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 you ng, adult, and older healthy humans as measured by their density on th e cell surface. Marker densities were calculated by fluorescence inten sity 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 statistica lly significant changes were observed with advancing age: (1) Increase d density of HLA-DR markers on CD3(+) and CD8(+) cells and CD4 markers in the ''adult'' group (ages >34 less than or equal to 59 years) (1.5 -fold, 0.5-fold, and 0.4-fold increases, respectively) when compared w ith the ''young'' group (ages less than or equal to 34 years); (2) dec reased density of HLA-DR markers on CD3(+) and CD8(+) cells and CD8 ma rkers in the ''older'' group (ages greater than or equal to 60 years) (0.2-fold, 0.5-fold, and 0.4-fold decreases, respectively) when compar ed with the adult group. However, when the ''older'' group was compare d to the young group, the density of HLA-DR markers on CD3 cells and t he density of CD4 markers and CD8CD57 markers were significantly highe r (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 fo rward light scatter, was uniformly smaller in the older age group when compared with the young group (29.5 +/- 0.4% 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 immunologic responsivenes s observed with increasing age. (C) 1995 Academic Press, Inc.