Augmentation of Megakaryocyte Expression of FcγRIIa by Interferon γ

Abstract

OBJECTIVE: The purpose of this study was to identify factors that alter expression of FcgammaRIIa by megakaryocytes. METHODS AND RESULTS: Effects of selected cytokines and growth factors on megakaryocyte expression of FcgammaRIIa were assessed with phorbol 12-myristate 13-acetate (PMA)-differentiated human erythroleukemia (HEL) cells and with thrombopoietin-differentiated CD34 stem cells and compared with those obtained with myelocytic cell lines and a monocytic cell lines. Expression of FcgammaRIIa was quantified with the use of Western blots and real-time reverse transcriptase-polymerase chain reaction. Megakaryocyte differentiation was identified by expression of CD41, CD42, and von Willebrand factor with the use of flow cytometry. Interferon (IFN) gamma increased protein expression of FcgammaRIIa by HEL cells and CD34 stem cells after megakaryocyte differentiation (maximal approximately 4-fold, P<0.001 for each). IFNgamma did not increase expression of FcgammaRIIa by undifferentiated HEL and CD34 cells. Expression of FcgammaRIIa mRNA was increased (2-fold, P<0.001) in megakaryocyte-differentiated HEL cells. IFNgamma did not increase expression of FcgammaRIIa by undifferentiated myelocytic or monocytic cell lines. CONCLUSIONS: IFNgamma appears to selectively increase expression of FcgammaRIIa by cells exhibiting characteristics of megakaryocytes. This effect of IFNgamma may contribute to greater platelet expression of FcgammaRIIa in patients with atherosclerotic vascular disease.