PROLIFERATIVE EFFECT OF POSTAPHERESIS PLATELET DONOR PLASMA ON A MEGAKARYOBLASTIC LEUKEMIA-CELL LINE

Platelet donors sometimes show an increased platelet count following a pheresis. We analyzed the effect of plasma obtained from such donors, along with thrombopoietin (Tpo), for growth and differentiation induci ng activity on a megakaryoblastic leukemia cell line, Meg-J. Colony fo rmation was stimulated by donor plasma for Meg-J cells in a dose-depen dent manner, and the time course of the sampling peaked 1 day after ap heresis. Neither the donor plasma nor Tpo induced morphological differ entiation. Donor plasma from any sampling time decreased CD41 and CD42 b expression by more than 10%, and more than a 10% decrease of CD41 wa s induced by Tpo. The measurement of plasma Tpo showed no statisticall y significant increase after platelet donation. Our data suggest that, following apheresis, donor plasma contains factor(s) that: (a) stimul ate growth rather than induce differentiation of a megakaryoblastic ce ll line; (b) are present in increased levels after apheresis; and (c) are different from Tpo.