Telomere length measurement and determination of immunosenescence-related markers (CD28, CD45RO, CD45RA, interferon-gamma and interleukin-4) in skin-homing T cells expressing the cutaneous lymphocyte antigen: indication of a non-ageing T-cell subset.

The 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-gamma (IFN-gamma) and interleukin-4 (IL-4) formation of CLA+ 'skin 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 fluorescence in situ hybridization using flow cytometry (flow 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-), which showed significantly decreased CD28 and CD45RA expression in donors > 60 years of age, no age-related 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-gamma-producing CD3+ CLA- cells showed a significant increase, whereas the number of IFN-gamma- 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 significantly shortened in enriched CD45RO+ CLA- 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 inflammatory skin reactions (e.g. psoriasis or eczema) seems to be independent of the patients' age.