The CD19 gene encodes a member of the immunoglobulin superfamily, which is almost exclusively expressed in B lymphocyte lineage cells and serves as a marker for pre-B cells. The Cd19-Cre mouse was constructed by inserting the Cre recombinase gene expression cassette into the mouse endogenous Cd19 gene, driving its specific expression. Downstream of this Cre recombinase gene expression cassette is connected a “Rabbitβ-globin intron” gene expression element, which can greatly enhance the expression of the upstream Cre recombinase gene. When these mice are crossed with mice containing loxP sites, sequence recombination between loxP sites mediated by Cre recombinase can occur in the B lymphocyte lineage cells of their offspring.