Age‐related accumulation of LFA‐1high cells in a CD8+CD45RAhigh T cell population

Abstract

The differential expression of CD45 isoforms has been suggested as a marker for stages of post‐thymic T cell development, that is, CD45RA+CD45R0⁻ T cells and CD45RA⁻CD45R0⁺ T cells are supposed to be virgin and memory cells respectively. Recently, several adhesion molecules have been shown to be up‐regulated on the cell surface of memory T cells, and have been suggested to serve as a memory marker. In this study, we investigated the levels of LFA‐1 expression on T cells in various subpopulations defined by CD45 isoform expression in donors of various ages.In CD4⁺ T cells, the proportion of LFA‐1^high cells among CD45RA^highCD45R0‐T cells remained low in all age groups and did not show significant accumulation with age. CD4⁺CD45RA⁻CD45R0^highTcells expressed LFA‐1 at a higher level than CD4⁺CD45RA^highCD45R0⁻ T cells. Thus, the currently prevailing view that CD45RA and CD45R0 can be markers for virgin and primed cells was consistent with LFA‐1 expression in CD4⁺ T cell population.In CD8⁺ T cells, however, CD45RA^highCD45R0⁻ T cells consisted of two distinct subpopulations, LFA‐1^low and LFA‐1^high cells, whereas CD45RA⁻CD45R0^high T cells were almost exclusively LFA‐1^high When CD29 expression was examined in place of LFA‐1 expression, similar results were obtained; CD45RA^high CD45R0⁻ T cells consisted of two distinct subpopulations, CD29‐^{to low} and CD^29high cells, while CD45RA‐CD45R0^high T cells were mostly CD29^high.The proportion of LFA‐1^high cells in the CD8+CD45RA^high T cell subpopulation increased significantly as a function of age (r = 0.9, p < 0.001). It ranged from 8% in a 14‐year‐old donor to 94% in a 79‐year‐old donor. Furthermore, the proportion of CD8⁺CD45RA^highLFA‐1^high cells in the CD8⁺ T cell population increased significantly as a function of age (r = 0.85, p < 0.001). On the other hand, the proportion of LEA‐1^high cells in CD8⁺CD45RA⁻ T cell subpopulation exceeded 90% in most donors irrespective of age.These results indicate that the CD8⁺CD45RA^highCD45R0⁻ T cell subpopulation contains a considerable number of LFA‐1^high cells and CD29^high cells, phenotypically similar to previously activated cells. Thus, in terms of LFA‐1 and CD29 expressions, the simple scheme that CD45RA is a marker of virgin cells is not applicable to the CD8⁺ T cell population.