IMMUNOBIOLOGY OF MOUSE DENDRITIC EPIDERMAL T-CELLS - A DECADE LATER, SOME ANSWERS, BUT STILL MORE QUESTIONS

Over the past decade, overwhelming evidence has accumulated in many sp ecies, most notably in mice, that epithelial sites such as skin, intes tine, and reproductive tract are populated with relatively discrete su bsets of gamma delta cells, Such studies have identified several disti nguishing and, in some cases, unique features of the dendritic epiderm al T cells (DETC) populating the skin of all normal mice: homogeneous V5-J1-C gamma/V1-D2-J2-C delta T-cell receptors devoid of junctional d iversity, apparent tissue restriction in adult mice to the skin, an im portant role for active hair growth in their localization and/or proli feration in the skin, and a capacity to recognize an antigen expressed on stressed epidermal cells, These properties have led to the hypothe sis that DETC play distinctive roles in cutaneous immune surveillance and/or immunoregulation via recognition of a common self-antigen expre ssed by adjacent cells under various potentially harmful circumstances , Despite substantive advances in our knowledge about gamma delta cell s in general (e.g., recent evidence that their manner of antigen recog nition may be fundamentally different from that used by conventional a lpha beta T cells) and about epithelial-specific subsets such as murin e DETC in particular, it is clear that, compared with our understandin g of alpha beta cells, major gaps still exist in our understanding of these cells, Persisting questions about DETC include: precise identifi cation of the ligands for their homogenous T-cell receptors, the cellu lar and molecular requirements for their activation, their full range of functional activities, the reason(s) for the absence in normal huma n skin of a precise morphologic and phenotypic homologue, and, perhaps most important, their biologically relevant role(s) in cutaneous phys iology, immunity, and/or pathology.