Biotinylated CD19 His&Avi Tag Protein, Human

CD19, also known as B-lymphocyte antigen CD19 or B4, is a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. Its structure comprises an extracellular region containing two immunoglobulin-like domains (one V-type and one C2-type), a transmembrane domain, and a cytoplasmic tail harboring multiple tyrosine phosphorylation sites that interact with Src family kinases (such as Lyn and Fyn) and PI3K signaling molecules. CD19 is specifically expressed throughout the B-lymphocyte lineage, from the pre-B cell stage through mature B cells, though it is downregulated at the plasma cell stage, serving as a critical co-stimulatory molecule for B cell activation, proliferation, and differentiation. Functionally, CD19 lowers the signaling threshold of the B cell receptor (BCR), enhancing the sensitivity of B cell responses to antigens, while also participating in B cell development, antibody class switching, and germinal center reactions. In recent years, CD19 has emerged as one of the most successful targets in tumor immunotherapy, with chimeric antigen receptor T cell (CAR-T) therapy directed against CD19 achieving breakthrough efficacy in B cell acute lymphoblastic leukemia (B-ALL) and diffuse large B cell lymphoma (DLBCL), and further expanding into the treatment of autoimmune diseases such as systemic lupus erythematosus and ulcerative colitis, demonstrating broad clinical application prospects.