Recent observations regarding interferon, keratinocytes and lymphocytes in vitro and in vivo.

The purpose of this presentation is 3 fold and includes the past, present, and future: L To review the concept of skin-associated lymphoid tissue (SALT) 2. To summarize the experimental work related to lymphocyte-keratinocyte reactions in vitro 3. To briefly outline interferon related therapeutic implications for dermatologists In the past few years, several review articles concerning the immunobiology of the skin have appeared (1-3). The initial skin biologists were concerned with understanding how the epidermis could influence and interact with lymphocytes. Analogies between thymic epithelium and epidermis were made and keratinocytes were found to be able to induce terminal deoxynucleotidyl transferase on T lymphocytes (4). Next, Chu et al. (5) demonstrated that keratinocytes peroduced a thymopoietin-like molecule which could also induce T-Iymphocyte differentiation. Most recently, keratinocytes have been found to produce an Interleukin-l factor (Epidermal Thymocyte Activating Factor, ETAF) which can augment the proliferation of partially stimulated lymphocytes (6, 7). With the discovery that epidermal Langerhans cells could function as specialized antigen presenting cells to T lymphocytes, there could be little doubt that the skin was more than a passive target for various immunologically-mediated insults, but rather was an active participant in