Response Of Epidermal Cells Research Articles

UVR induction of TGF alpha: a possible autocrine mechanism for the epidermal melanocytic response and for promotion of epidermal carcinogenesis.

The occurrence of the epidermal growth factor homologue, transforming growth factor alpha (TGF alpha), in embryonic and neoplastic tissues suggests that it may be an oncofetal version of epidermal growth factor. A strong case is developing for TGF alpha to have an autocrine mode of action in sustaining the autonomous growth of several types of tumour. We propose that TGF alpha normally has an autocrine role not only in stimulating the growth of some fetal tissues but also with postnatal epidermal cells in response to local stimuli--in particular ultraviolet radiation (UVR). As a first step to test this hypothesis we have checked whether UVR will induce the production of TGF alpha, measured by radioimmunoassay, using a highly specific monoclonal antibody which recognizes native, biologically active human TGF alpha. We found that cultures of normal foreskin melanocytes do not produce detectable amounts of TGF alpha when grown under routine conditions, but, within 12 h of exposure to low doses of short-wavelength UVR, significant quantities of TGF alpha are produced. The UVR-induced TGF alpha is both cell associated and released into the medium of these cultures. Also, UVR has a promoting action on epidermal cells which have been initiated by carcinogenic activity. A significant part of the promoting activity may be due to autocrine stimulation of multiplication of partially transformed epidermal cells. In this regard we found that UVR induced TGF alpha in HeLa cells and all human melanoma lines so far tested. Induction was complete within 24 h of a single exposure. Dose-response curves of TGF alpha induction in a malignant melanoma cell line showed a distinctive peak of factor induced by low (2 J/m2) doses of UVR. Higher doses which inhibit [3H]thymidine incorporation resulted in lower levels of induced TGF alpha. These findings are consistent with the participation of TGF alpha as an autocrine mediator of UVR-induced tumour promotion, as well as cell multiplication, in sun-exposed skin.

The inheritance of mechanisms of partial resistance to Erysiphe graminis in spring barley

The response of epidermal cells to attempted penetration by Erysiphe graminis was examined in the fifth leaf of 13 barley lines selected for partial resistance. In leaf segments fixed and stained 72 h after inoculation cell reactions were classified as susceptible or as exhibiting non‐hypersensitive or hypersensitive resistance. The proportion of cells with each type of reaction varied in a continuous manner among the lines and there were significant differences between lines in the levels of non‐hypersensitive and hypersensitive resistance. Crosses were made between lines exhibiting high and low levels of each resistance mechanism. Fifty challenged epidermal cells per duplicate leaf segment were examined on 45‐50 F2 plants derived from two such crosses. The frequency distribution of each of the three types of cell reaction in the fifth leaf was found to be continuous and, in general, normally distributed and in no case was there a significant difference between parent and progeny mean values, suggesting that the two resistance mechanisms were under the control of several genes showing predominantly additive gene action.

Experimental toxic and allergic contact dermatitis: II. A histopathologic study

Chronologic development of histologic changes at the site of allergic and toxic dermatitis is described in detail. Mononuclear cell invasion, vacuolization, vesicle formation, and exfoliation of the epidermis are steps in a process characteristic of the allergic response. A comparison of the histologic and chemical changes in toxic and allergic dermatitis indicates that sensitization induced a capacity in the mononuclear cells for positive chemotaxis, for induction of characteristic inflammatory changes, and for participation in metabolic processes (presumably by increased enzymatic activity). A sensitization of epidermal cells has not been ruled out. An extreme acanthosis seen in allergic lesions of animals treated with germanin might be regarded as the allergic response of epidermal cells after participation of mononuclear cells has been forestalled.