Expression of metallothioneins-I and -II isoforms at positive patch-test sites

The expression and the distribution of metallothioneins (MT)-I and II isoforms were evaluated in 5 healthy volunteers and in 16 subjects with positive patch test reactions to various compounds. Skin specimens taken both from the healthy skin of the back and at positive patch test sites (at 48 h), were treated using a 3-step indirect immunoperoxidase procedure with a mouse monoclonal IgG1 antibody reactive against I and II isoforms of human, rat and horse MT. MT were expressed in the basal layer of the healthy skin of both controls and sensitive subjects, without any significant difference. At positive patch test sites, there was an overexpression of MT in basal and suprabasal layers of the epidermis. Overexpression of MT, related to the degree of the inflammatory reactions elicited by the penetrating compounds was observed in the dermis. The cells expressing MT in the dermis were mostly T lymphocytes and cells with dendritic morphology which positively stained in part for CD34 and in part for XIIIa markers and negatively for KP1, S100 and HLA-DR. Taken together, these results seem to indicate that MT represent a constitutive mechanism of defence expressed by different types of cells in the skin, which is triggered by contact with both metallic and non-metallic compounds. The biological significance of MT in the skin remains to be elucidated. Our preliminary findings do not permit evaluation of whether these nearly ubiquitous proteins exert their cytoprotective effects in the skin acting simultaneously as antioxidant, metal binding or zinc suppliers, or if they display these activities mainly depending on the nature of the penetrating substances.