EXTRACORPOREAL PHOTOCHEMOTHERAPY (PHOTOPHERESIS) INDUCES APOPTOSIS INLYMPHOCYTES - A POSSIBLE MECHANISM OF ACTION OF PUVA THERAPY

The mechanism of action of psoralen plus UVA (PUVA) and photopheresis is not entirely understood, These therapies are assumed to be immunomo dulating partly by gradually decreasing leukocyte viability, We invest igated whether this delayed form of cell death was due to apoptosis, U ntreated and treated (PUVA exposed) leukocytes obtained from six patie nts with systemic sclerosis and (untreated) leukocytes from healthy co ntrol individuals were studied, Qualitative gel electrophoresis and qu antitative in situ nick translation analysis of DNA fragmentation was performed, Apoptosis of the treated cells did occur (gel electrophores is) after 24 h, At t = 0 h, immediately after exposure to PUVA, there was no evidence of DNA fragmentation in the treated cells, The percent age of treated cells undergoing apoptosis was 20-55% at t = 24 h (in s itu nick translation), The untreated leukocytes of the patients and th e healthy individuals showed no distinctive rise in apoptotic cells. A poptosis of the leukocytes after PUVA or photopheresis treatment might be a mechanism of action and might explain the therapeutic response.