Transition from symptomless to lesional psoriatic skin.

Numerous investigations have been carried out to describe the cellular biological changes in lesional and symptomless psoriatic skin. Although these studies have increased our knowledge of the pathogenesis of psoriasis, our insight into the relevance of the individual changes in the whole pathogenic process is still limited. Studies on the transition between symptomless and lesional skin are of importance in assessing the pathogenic relevance of the individual aspects. In this paper, the literature is reviewed with respect to the transitional changes; in particular, studies on changes at the margin of the psoriatic lesion and the response of the symptomless skin to standardized injury are reviewed. From the available studies it may be concluded that changes in the stroma (i.e. increased expression of tenascin and increased endothelial alkaline phosphatase activity) are early pathogenic features. The appearance of a predominantly lymphocytic infiltrate, in particular the extravasation of CD4+ T lymphocytes, and the suprabasal expression of keratin 16 are intermediary stages. Relatively late in the pathogenesis are increased recruitment of cycling epidermal nuclei, parakeratosis, decreased expression of filaggrin and premature expression of involucrin. In order to discover the pathogenic relevance of molecules which might have an impact on the development of psoriasis, sequential studies during transition from symptomless to lesional skin are worthwhile.