Functional expression of IgA receptor FcαRI on human platelets

FcαRI (CD89) is a human IgA FcR expressed on cells of myeloid lineage such as neutrophils, monocytes, tissue macrophages, eosinophils, and subpopulations of dendritic cells. FcαRI mediates cell activation through Src family kinases and downstream tyrosine-based phosphorylation pathways. However, the role of IgA and the expression and role of its cognate receptor FcαRI (CD89) in platelet activation are undefined. In the current study, we demonstrate that human platelets express FcαRI mRNAs and proteins. Furthermore, we show that the platelet FcαRI is associated with the FcR γ-chain, and cross-linking of FcαRI leads to Syk phosphorylation. Clustering of FcαRI induces pre-mRNA splicing and protein production of tissue factor and IL-1β, suggesting novel roles for human platelet FcαRI and serum IgA in thrombosis and inflammation.