Quantitative and qualitative changes in CD44 and MEL-14 expression by T cells in C57BL/6 mice during aging

Aging is associated with a decrease in the functional activity of T cells. We have explored age-related alterations in CD44 and MEL-14 expression by spleen cells bearing the Thy1.2, CD4 or CD8 antigens in C57BL/6 mice at 2, 8, 15 and 23 months of age. The membrane expression of CD44 and MEL-14 molecules can be used to distinguish naive (CD44low, MEL-14high) from preactivated/memory (CD44high, MEL-14low) T cells. Our results show that the proportion of CD4+ splenic cells begins to decrease at an intermediate age (8-month-old mice), whereas the proportion of CD8+ cells remains unaltered. The proportion of CD4+ and CD8+ splenic cells with the CD44high memory phenotype was increased at an early stage of aging (in 8-month-old mice) without a concomitant change in MEL-14 expression. In older mice, MEL-14 expression decreased on CD4+ but not on CD8+ subsets. Recent studies have reported that following activation, the expression of CD44 molecules containing additional, so-called variable exons can be detected. By PCR, we observed an increase in CD44 transcripts containing the v6 or v7 variable exons in murine lymph nodes at the age of 15 months. Our results suggest that v6- or v7-containing variants of CD44 may be involved in the development of memory cells. Taken together, these results suggest that the trafficking of memory T cells in aging may be altered by quantitative and/or qualitative differences in the expression of molecules involved in lymphocyte recirculation.