Expresison of Fc(γ)RII and CD4 receptors by normal human megakaryocytes

We studied human megakaryocytes to determine if they both expressed and synthesized Fc(γ) and CD4 membrane receptors. The strategy employed relied on demonstration of receptor protein and mRNA in megakaryocytes present in freshly made marrow smears, or in megakaryocytes isolated from aspirated normal bone marrow by counterflow centrifugal elutriation. Protein was detected immunochemically, whereas mRNA was detected either by in situ hybridization, or by reverse transcription, polymerase chain reaction (RT-PCR). Using these methods CD4 and Fc(γ)RII protein and mRNA were detected in most megakaryocytes. Fc(γ)RI and Fc(γ)RIII protein was not detected in these cells. Megakaryocytes were also cultured with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) to determine the effect of this growth factor on Fc(γ)RII expression. As has been noted in cells of the monocyte-macrophage lineage, exposure to rhGM-CSF resulted in a significant increase in the level of megakaryocyte Fc(γ)RII mRNA and protein. These observations are significant because they provide a physiologic basis for known viral trophism displayed by megakaryocytes. They are also of interest because they suggest that alternative portals exist for entry of human immunodeficiency virus (HIV-1) into megakaryocytes and that such infection may play a role in acquired immunodeficiency syndrome (AIDS)-related thrombocytopenia.