DERMAL DENDRITIC CELLS ASSOCIATED WITH T-LYMPHOCYTES IN NORMAL HUMAN SKIN DISPLAY AN ACTIVATED PHENOTYPE

The CMRF-44 and CD83 (HB15) antigens are associated with functional ma turation and activation of blood dendritic cells (DC). We describe the expression of these antigens on freshly isolated epidermal Langerhans cells and dermal DC as well as the distribution of CD83(+)/CMRF-44(+)-activated DC within sections of normal human skin. Fresh Langerhans cells were prepared by standard techniques and large numbers of enrich ed (25%-55%), viable dermal DC were obtained using an improved collage nase treatment protocol with density gradient enrichment, Freshly isol ated Langerhans cells and dermal DC had similar costimulator and activ ation antigen expression, and both stimulated moderate levels of allog eneic T lymphocyte proliferation as determined in the 7 d mixed leukoc yte reaction. In situ labeling of DC within skin sections revealed a p opulation of CD83 and CMRF-44 positive dermal cells of which most (app roximate to 75%) were in intimate contact with CD3(+) T lymphocytes, e specially in the adnexal regions. In contrast, only 25%-30% of the mor e numerous CD1a(++) dermal DC population were directly apposed to T ly mphocytes. The CMRF-44(++) dermal DC population stimulated an allogene ic mixed leukocyte reaction, confirming their identity as DC. These da ta, plus comparative data obtained for migratory dermal DC, suggest th at only a small proportion of dermal DC have been triggered to a more advanced state of differentiation or activation. The striking associat ion of the activated dermal DC population with T lymphocytes suggests that communication between these two cell types in situ may occur earl y in the immune response to cutaneous antigen.