The CD19 protein is a B cell antigen receptor coreceptor that enhances downstream signaling pathways, lowers the activation threshold, and helps B cells respond to antigens. It activates phosphatidylinositol 3-kinase and mobilizes intracellular Ca (2+) . CD19 Protein, Human (Biotinylated, HEK293, Fc) is the recombinant human-derived CD19 protein, expressed by HEK293 , with C-Avi, C-hFc labeled tag.