[Remarks on contact eczemas--etiopathogenetic considerations based on immunohistochemical studies]

Functionally defined inflammatory cells can be selectively labeled in tissue sections by immunohistochemical methods. We investigated the cellular infiltrate in acute toxic contact dermatitis and various forms of contact eczema and other inflammatory dermatoses. In all cases, the so-called "superficial T-cell pattern" was evident, which comprised T-lymphocytes, predominantly helper/inducer cells, as well as Langerhans cells/indeterminate cells. The numerical density of these cell types, which represent the cellular prerequisites for delayed hypersensitivity reactions, turned out to be markedly increased in affected skin. Compared with normal skin, therefore, lesional skin provides a different immunological microenvironment. We conclude that a negative patch test reaction in normal skin does not exclude the possibility that the same allergen may provoke and enhance immunological reactions in eczematous skin. Eczema is regarded as an abnormal reaction of the organism towards exogenous factors; the abnormal reaction may be confined to sites with a considerable infiltrate. This might explain the pronounced chronicity of contact eczemas, even after withdrawal of the presumed cause, and the existence of chronic allergic contact eczemas without positive patch test results. The inflammatory infiltrate may be interpreted as a major predisposing factor for further immunological reactions at the same site.