Ultrastructural changes in nuclei and nucleoli in psoriatic epidermis during and after PUVA therapy.

Quantitative and qualitative changes of the nuclei and nucleoli in psoriatic epidermis at different intervals during therapy with psoralen and long-wave ultraviolet light (PUVA) were revealed with the electron microscope. Early in the therapy (24 to 96 hr after commencing treatment) changes occur, including irregularity of the nuclear envelope, enlargement of the nuclei and nucleoli, temporary disappearance of fibrillar centres, followed by temporary disappearance of fibrillar centres, followed by temporary increase in nuclear bodies and increasing amounts of heterochromatin. After clearing of lesions, the nuclear and nucleolar structures were identical with those of normal keratinocytes, except that the relative amount of heterochromatin was greater. It is suggested that PUVA therapy brings about inhibition of abnormal keratinization, possibly due to gene repression, and that this may be related to changes in the fibrillar centres of psoriatic keratinocyte nucleoli.