Identification of IgG Fc receptor type II on human megakaryoblastic cell lines (MEG‐01 and UT‐7)

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Abstract
In this study, Fc gamma receptors (Fc gamma R) on the cells of human megakaryoblastic leukaemia cell lines (Meg-01 and UT-7) were investigated. Binding of the anti-Fc gamma RII monoclonal antibody (MoAb) IV. 3 but not anti-Fc gamma RI MoAb (32.2), anti-Fc gamma RIII MoAb (3G8) nor control murine IgGs to Meg-01 and UT-7 cells was demonstrated by immunocytochemical staining and flow cytometric analysis. There was specific and saturable binding of 125I-labelled IV.3 Fab fragments to the megakaryoblasts but no binding of 125I-labelled 32.2 Fab nor 3G8 Fab fragments. MoAb IV.3 immunoprecipitated a 40 kD protein (Fc gamma RII) from detergent cell lysates of surface radiolabelled Meg-01 and UT-7 cells. More importantly, IV.3 Fab almost completely inhibited the binding of 125I-labelled human aggregated IgG to the Meg-01 cells. In contrast, neither 32.2 Fab, 3G8 Fab nor Fab fragments of the control murine IgGs were inhibitory. These results indicate that only Fc gamma R Type II is expressed on megakaryoblasts in these two cell lines.