Cluster of differentiation 19 (CD19) is a cell surface protein found on B cells that plays an important role in its development and activation. Since CD19 is predominantly expressed in B lymphocytes, it can be used as a biomarker for B lymphocyte malignancies, such as chronic lymphocytic leukemia (CLL), non-Hodgkin lymphoma, and acute lymphoblastic leukemia (ALL). CD19 can also be used a target for immunotherapy, such as CAR T-cell therapy, which utilizes engineered T-cells to target CD19 on tumor B cells. Signosis’ Human CD19 ELISA kit can accurately measure CD19 levels in human samples and provides a human CD19 protein standard for quantitative analysis.