Organ culture of psoriatic lesions: appearance of granular layers in vitamin A-free culture media.

Some morphologic changes of the epidermis of psoriatic skin were observed in organ culture in the presence of absence of vitamin A. Normal and uninvolved and involved psoriatic skin areas, punch biopsied in 3-4-mm diameter specimens, were put in serum-free medium containing no vitamin A with or without delipidized fetal calf serum (FCS) and rotation cultured at 60 rpm under an atmosphere consisting of 95% O2 + 5% CO2. The involved psoriatic skin specimens showed well-developed granular layers after 1 d of culture. The values of labeling indices of 3H-thymidine (3H-TdR) incorporated into the epidermal layers of the cultured specimens of the psoriatic skin were nearly constant during culture for as long as 8 d, although the viable epidermal layer gradually became thinner. Addition of tretinoin to the culture caused uninvolved and involved psoriatic skin specimens to become parakeratotic at concentrations as low as about 2.0 x 10(-6) M and 4.0 x 10(-8) M, respectively, suggesting that the involved psoriatic epidermis is much more sensitive, in terms of keratinization, than uninvolved epidermis to the effect of tretinoin.