The cluster of differentiation 19 (CD19) gene encodes a member of the immunoglobulin gene superfamily, whose expression is restricted to B lymphocytes and is a marker of pre-B cells. In humans, CD19 is expressed on all cells of the B lymphoid lineage except plasma cells and follicular dendritic cells. CD19 acts as an adapter protein to recruit cytoplasmic signaling proteins to the membrane and acts within the CD19/CD21 complex to lower the threshold of the B cell receptor signaling pathway. The protein is a biomarker for B lymphocyte development and lymphoma diagnosis and may serve as a target for leukemia immunotherapy. Mutations in this gene are associated with common variable immunodeficiency 3 (CVID3) disease, which is characterized by hypogammaglobulinemia, failure to mount an antibody response to antigen, and recurrent bacterial infections, and certain loss-of-function mutations in this gene also fails B cell differentiation and impaired immunoglobulin secretion.

CD19-Cre mice were constructed by inserting a Cre recombinase gene expression element into the endogenous Cd19 gene of mice to drive its specific expression. A Rabbit β-globin intron is attached downstream of the Cre recombinase gene expression element, which can greatly increase the expression level of Cre recombinase. When this strain is crossed with mice containing the loxP locus, sequence recombination between loxP loci mediated by Cre recombinase can occur in the majority of B-lymph spectrum cells of the offspring mice.