AGE-RELATED ACCUMULATION OF LFA-1(HIGH) CELLS IN A CD8-CELL POPULATION(CD45RA(HIGH) T)

The differential expression of CD45 isoforms has been suggested as a m arker for stages of post-thymic T cell development, that is, CD45RA+CD 45R0- T cells and CD45RA-CD45R0+ Tcells are supposed to be virgin and memory cells respectively. Recently, several adhesion molecules have b een shown to be up-regulated on the cell surface of memory Tcells, and have been suggested to serve as a memory marker. In this study, we in vestigated the levels of LFA-1 expression on Tcells in various subpopu lations defined by CD45 isoform expression in donors of various ages. In CD4+ Tcells, the proportion of LFA-1high cells among CD45RA(high)CD 45R0- T cells remained low in all age groups and did not show signific ant accumulation with age. CD4+CD45RA-CD45R0high T cells expressed LFA -1 at a higher level than CD4+CD45RA(high)CD45R0- Tcells.Thus, the cur rently prevailing view that CD45RA and CD45R0 can be markers for virgi n and primed cells was consistent with LFA-1 expression in CD4+ Tcell population. In CD8+ T cells, however, CD45RA(high)CD45R0- T cells cons isted of two distinct subpopulations, LFA-1low and LFA-1high cells, wh ereas CD45RA-CD45R0high Tcells were almost exclusively LFA-1high. When CD29 expression was examined in place of LFA-1 expression, similar re sults were obtained; CD45RA(high)CD45R0-T cells consisted of two disti nct subpopulations, CD29-to low and CD29high cells, while CD45RA-CD45R 0high T cells were mostly CD29high. The proportion of LFA-1high cells in the CD8+CD45RA(high) T cell subpopulation increased significantly a s a function of age (r = 0.9, p < 0.001). It ranged from 8% in a 14-ye ar-old donor to 94% in a 79-year-old donor. Furthermore, the proportio n of CD8+CD45RA(high)LFA-1high cells in the CD8+ T cell population inc reased significantly as a function of age (r = 0.85, p < 0.001). On th e other hand, the proportion of LFA-1high cells in CD8+CD45RA- T cell subpopulation exceeded 90% in most donors irrespective of age. These r esults indicate that the CD8+CD45RA(high)CD45R0- T cell subpopulation contains a considerable number of LFA-1high cells and CD29high cells, phenotypically similar to previously activated cells. Thus, in terms o f LFA-1 and CD29 expressions, the simple scheme that CD45RA is a marke r of virgin cells is not applicable to the CD8+ T cell population.