Absolute numbers of CD3+ T lymphocytes and their subpopulations were determined and statistically evaluated in the lesional skin of psoriasis, atopic dermatitis, nummular dermatitis, pityriasis rosea, and lichen planus. Skin sections were divided into horizontal layers and the numbers of CD3+ T cells as well as CD4+ inducer and CD8+ suppressor-cytotoxic T-cell subsets were counted. In addition, absolute numbers of the two subpopulations of inducer T cells, i.e., “memory” (4B4+ 2H4-) and “naive” (4B4- 2H4+) were evaluated. Unexpectedly, epidermal infiltration by T cells was highest in psoriasis and lowest in atopic dermatitis. In most cases, this exocytosis was dominated by CD8+ suppressor/cytotoxic T lymphocytes, with a minimal epidermal mean CD4/mean CD8 ratio of 0.04 in pityriasis rosea and a maximum of 0.48 in psoriasis. Inducer T cells within the epidermis were almost exclusively of the 4B4+ 2H4- “memory” T-cell subpopulation, whereas 4B4- 2H4+ “naive” T cells were extremely uncommon in lesional epidermis. Similar results were obtained for dermal T cells in all diseases studied, i.e., 4B4- 2H4+ “naive” T cells were relatively rare. Papillary dermis infiltration by T cells was highest in lichen planus where a mean CD4/mean CD8 ratio of 1.10, the minimum in this comparative study, was obtained. The mean CD4/mean CD8 ratio of the papillary infiltrate was highest in atopic dermatitis (4.12). Our results indicate disease-specific and significantly different infiltration patterns of T-lymphocyte subsets in the chronic inflammatory dermatoses investigated. The predominant presence of the CD4+ 2H4- “memory” subpopulation of CD4+ T cells in all diseases studied as well as in normal human skin (reported previously) seems to indicate that the skin immune system is rather unidirectional in its increase in this subpopulation of the inducer T-cell subset. This predominance of the “memory” subpopulation thus indicates that most T cells of normal and diseased human skin are already primed, i.e., have already met their specific ligand in a MHC II context.
Memory T cells Naive T cells Immunodermatopathology Skin immune system T-cell subsets