Proliferative effect of postapheresis platelet donor plasma on a megakaryoblastic leukemia cell line

Platelet donors sometimes show an increased platelet count following apheresis. We analyzed the effect of plasma obtained from such donors, along with thrombopoietin (Tpo), for growth and differentiation-inducing activity on a megakaryoblastic leukemia cell line, Meg-J. Colony formation was stimulated by donor plasma for Meg-J cells in a dose-dependent manner, and the time course of the sampling peaked 1 day after apheresis. Neither the donor plasma nor Tpo induced morphological differentiation. Donor plasma from any sampling time decreased CD41 and CD42b expression by more than 10%, and more than a 10% decrease of CD41 was induced by Tpo. The measurement of plasma Tpo showed no statistically significant increase after platelet donation. Our data suggest that, following apheresis, donor plasma contains factor(s) that: (a) stimulate growth rather than induce differentiation of a megakaryoblastic cell line; (b) are present in increased levels after apheresis; and (c) are different from Tpo.