Abstract: Objective To study the abnormal proliferation and differentiation of keratinocytes in psoriasis, the distribution of type I transglutaminase was detected and analysed in situ using immunohistochemistry assay. Methods Frozen sections of skin biopsy specimens taken from the skin lesions of unexposed area of psoriasis patients and from the skin of the same area of normal controls were incubated with mouse anti human transglutaminase monoclonal antibody, and detected by peroxidase-labeled goat anti-mouse antibody with AEC as substrate. Results In normal control, positive staining was only seen between keratinocytes of granular layer, but in psoriatic lesions, it was observed throughout the whole epidermis except the basal layer, the intensity was strongest in granular layer, and spread to spinous cell layer with declining intensity. There was a significant difference in the intensity between normal control and psoriasis (P<0.01). Conclusion An undue early activation of the expression of Tgase I may be one of the causes of over expression of Tgase I in psoriasis, and retinoic acid can inhibit the expression of Tgase I in keratinocytes which may be one of the mechanisms of its therapeutical effects for the disease.

Key words: Psoriasis, Transglutaminase