The CD19 protein acts as a coreceptor for B cell antigen receptors, lowering the signaling threshold and initiating B cell responses to antigens. It activates a cascade leading to PI3K activation and Ca (2+) mobilization. CD19 Protein, Mouse (HEK293, His) is the recombinant mouse-derived CD19 protein, expressed by HEK293 , with C-His labeled tag.