The expression and the distribution of metallothioneins (MT)-I and II isofo
rms 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), we
re treated using a 3-step indirect immunoperoxidase procedure with a mouse
monoclonal IgG1 antibody reactive against I and II isoforms of human, rat a
nd horse MT. MT were expressed in the basal layer of the healthy skin of bo
th controls and sensitive subjects, without any significant difference. At
positive patch test sites, there was an overexpression of MT in basal and s
uprabasal layers of the epidermis. Overexpression of MT, related to the deg
ree 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 represe
nt a constitutive mechanism of defence expressed by different types of cell
s in the skin, which is triggered by contact with both metallic and non-met
allic compounds. The biological significance of MT in the skin remains to b
e 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.