PUVA apoptotic response in activated and resting human lymphocytes

In extracorporeal photopheresis (ECP) collected cells are treated by 8 methoxypsoralen and UVA (PUVA) which induced apoptosis. The mechanism of action of reinfused cell is unclear. A vaccination model postulates an efficient presentation of apoptotic alloreactive cells to the patient immune system. The efficiency may depend upon a predominence of apoptotic alloreactive cells after PUVA. Such selectivity could result from their activation. We studied apoptosis in resting and PHA-activated lymphocytes. Both were equally susceptible. Changes in early apoptosis were possibily missed. We evaluated the effect of preincubation before PUVA. During preincubation monocyte could affect lymphocytes susceptibility to apoptosis as an increase of number of apoptotic cells was observed after 72 hours in stimulated and resting cells.

Our findings do not preclude a selectivity of other PUVA effects since expression of membrane marker also targets to PUVA is modified by activation.