CD50 and CD62L Adhesion Receptor Expression on Naive (CD45RA+) and Memory (CD45RO+) T Lymphocytes in the Elderly

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Abstract
A complex reshaping characterizes cellular immunity in the elderly. In particular, the hallmark of the ‘senescence’ of the T cell compartment is a decrease in the proportion of CD45RA+ naive T lymphocytes concomitantly with an expansion of CD45RO+ memory T cells. However, in addition to age-dependent changes in their representation, phenotypical and functional anomalies also characterize naive and memory T cell populations in the elderly. Since cell adhesion molecules (CAMs) are multifunctional receptors which play important roles not only in cell-to-cell and cell-to-matrix interactions but also in signal transduction and cell activation, we analysed, by means of a three-colour flow cytometry method, the proportion, absolute number and density expression or mean fluorescence intensity (MFI) of CD50 (ICAM-3) and CD62L (L-selectin homing receptor) adhesion receptors on CD45RA+ and CD45RO+ peripheral blood CD3+ T cell subsets from 10 healthy elderly subjects and 10 young controls. Our aim was to investigate age-dependent changes in the expression pattern of these CAMs on naive and memory lymphocytes which might contribute to the remodelling of the immune system in the elderly. We considered the mean values ± standard deviations of the percentage, absolute number and MFI of positive cells. The percentage of naive T cells expressing CD50 was not significantly modified in aged (94.8 ± 5.0%) compared to young individuals (97.8 ± 3.2%). On the contrary, the percentage of memory T cells exhibiting CD50 was lower in elderly than young donors (92.0 ± 6.4 vs. 98.3 ± 2.2%; p < 0.01). The percentage of naive T cells expressing CD62L was decreased in the elderly donors (53.3 ± 18.8 vs. 80.8 ± 11.0%; p < 0.001), whereas the proportion of CD62L+ memory T lymphocytes was substantially comparable between the two age groups (63.5 ± 15.7 vs. 54.7 ± 12.3%). The absolute number per mm3 of CD50+ naive T cells from aged individuals was decreased (251.9 ± 141.9 vs. 621.8 ± 238.0/mm3; p < 0.001), whereas memory peripheral blood T lymphocytes expressing CD50 were substantially unchanged (863.8 ± 260.9 vs. 802.7 ± 139.6/mm3). On the contrary, the absolute numbers per mm3 of naive and memory peripheral blood T lymphocytes exhibiting CD62L were respectively decreased (190.8 ± 133.4/mm3) and increased (515.1 ± 146.8/mm3) in elderly donors compared to young controls (601.3 ± 129.1 and 351.8 ± 195.0/mm3; p < 0.001 and p < 0.05, respectively). Finally, CD50 MFI values of naive as well as memory T cell subpopulations from aged subjects were increased compared to young donors (14.0 ± 2.0 vs. 9.8 ± 1.2 and 14.0 ± 2.0 vs. 11.6 ± 1.3; p < 0.001 and p < 0.01, respectively). CD62L was also overexpressed in both naive (8.4 ± 1.6 vs. 6.7 ± 1.4; p < 0.05) and memory (10.3 ± 2.5 vs. 5.4 ± 1.1; p < 0.001) T subsets in the elderly. CD50 and CD62L upregulation could be interpreted as a compensatory mechanism for a decreased responsiveness and a greater requirement for activation signals rather than an age-related anomaly.