Morphology and frequency of heterochromatic nuclear sheets in normal circulating human leucocytes and after PUVA therapy.

'Heterochromatic nuclear sheets' are structures that extend out from the nucleus into the cytoplasm where they are limited on both sides by the nuclear envelope. A uniform terminology regarding these structures has not been agreed upon and an attempt has been made in the present study to clarify the nomenclature. The frequency of nuclear sheets in circulating leucocytes has been established for the first time and found to be 4-8% for granulocytes and 1-2% for agranulocytes. Nuclear sheets have been reported to be associated with leukaemia, aneuploidy and treatment with antimitotic drugs. The parameter was therefore used to test the effect of photo-activated 8-methoxy psoralen (PUVA therapy) on circulating leucocytes. Used for the treatment of psoriasis PUVA therapy has been reported to cause leukaemia, chromosomal aberrations, mutations and skin cancer. No increase in heterochromatic nuclear sheets was found.