CD19 is a cell surface protein member of the large immunoglobulin superfamily that complexes with CD21, CD81, and CD225 in the membrane of mature B-cells. A major function of CD19 is to assemble with the antigen receptor of B-lymphocytes to decrease the threshold for receptor-dependent stimulation, thus enhancing the specificity and sensitivity of B-cells towards antigens. CD19 plays a large role in regulating B-cell growth.
