SUMMARYThe purpose of this study was to investigate the immunosenescence of skin-homing T cells expressing the cutaneous lymphocyte antigen (CLA). Peripheral blood lymphocytes from 72 healthy individuals (33 male and 39 female; median age 54 years; age-range: 18±94 years) were investigated. The expression of CD28, CD45RA and CD45RO, as well as intracellular interferon-g (IFN-g) and interleukin-4 (IL-4) formation of CLA `s kin homing' T cells, was analysed. In addition, T cells were detected immunohistologically in skin specimens from 15 young and 15 old, healthy individuals. The relative telomere length (RTL) was measured by¯uorescence in situ hybridization using¯ow cytometry (¯ow FISH). The total number of CLA T cells was found to remain constant with increasing age. In contrast to peripheral blood T cells (CD3 CLA À ), which showed signi®cantly decreased CD28 and CD45RA expression in donors >60 years of age, no agerelated alterations of either CD28 CLA T cells or CD45RA CLA T cells were observed. In the group of donors >60 years of age, the proportion of intracellular IFN-g-producing CD3CLA À cells showed a signi®cant increase, whereas the number of IFN-g-and IL-4-producing CLA T cells was not affected by age. After stimulation with phytohaemagglutinin (PHA) or staphylococcal enterotoxin B (SEB), CLA T cells from old donors did not show a reduced response compared with CLA T cells from young donors. Additionally, the counts of T cells in healthy skin from young and old adults were statistically not different. Furthermore, the RTL was signi®cantly shortened in enriched CD45RO CLA À T cells from healthy old individuals, but not in aged CLA T cells. The present data suggest that CLA T cells might be a T-cell subpopulation which does not undergo immunosenescence. This may explain why the intensity of in¯ammatory skin reactions (e.g. psoriasis or eczema) seems to be independent of the patients' age.

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