The role of fibroblasts in the differentiation of the epidermis and its relationships with other somatic cells, specifically, keratinocytes, are studied using a skin equivalent formed from various types of fibroblasts separated from thoracic skin of a healthy donor, apparently healthy skin sites and plaques from a patient with psoriasis, keloids and upper eyelid skin of a normal subject, and keratinocytes separated from the umbilical skin of a newborn. Fibroblasts are shown to be active participants in the differentiation and formation of epidermis specificity. Various types of fibroblasts form a histologically different skin equivalent possessing the specific properties of the epidermis of the skin sites from which they were isolated. Key Words: fibroblasts; keratinocytes; skin equivalent; cell-to-cell cooperationUnraveling the mechanisms of cell-to-cell cooperation realized in the course of the immune response would definitely contribute toward solving problems in experimental and clinical immunology, dermatology, and transptantology. Disorders of this cooperation are interesting for pharmacology as well. Recent experimental and clinical findings have confirmed that fibroblasts (FB), which are both somatic and immunocompetent cells, play a key role in the mechanisms of interaction between immunocompetent cells and in the regulation of proliferation, differentiation, and migration of somatic cells [2][3][4].However, these reports are often contradictory and superficial. This study was aimed at elucidating the role of FB as the principal factor in the specific differentiation of the epidermis. MATERIALS AND METHODSHuman dermal FB and keratinocytes (KC) were used in the study. FB were separated from the thoracic Russian State Medical University, Moscow; Department of Dermatology and Department of Ophthalmology, University of Texas, Houston (Presented by R. V. Petrov, Member of the Russian Academy of Medical Sciences) skin of healthy donors and psoriasis patients and isolated from apparently healthy skin sites of patients with psoriasis. In addition, FB were isolated from keloids and upper eyelid skin of normal subjects. KC were separated from the umbilical skin of newborns or from the skin of adult donors.Isolation of FB and KC from skin biopsy specimens. FB were isolated by two methods using 1) collagenase [5] and 2) slides: the derma was cut into 0.5 to 1.0 mm fragments, put in a 3-cm petri dish, covered with a slide, and incubated until FB started to migrate from the fragments onto the bottom of the dish. After 50% fusion was attained by trypsin treatment, the FB were transplanted to a flask.In other experiments a preseparated (using the method described above) dermal component of the skin was placed in a culture flask with collagenase for 1-2 h of incubation. The cells were then repeatedly resuspended and washed in DMEM medium (analog of medium 199) with 10% bovine serum, and then centrifuged at 600 g/min (MLW) for 7 rain.In the next step the ceils were transferred to special 75-ml plastic cuvettes, DMEM growt...