Expressed throughout B-lymphocyte development from the pro-B cell through the mature B-cell stages. BD Horizon™ BV480 Rat Anti-Mouse CD19 participates in B-lymphocyte development, B-cell activation, maturation of memory B cells and regulation of tolerance. CD19 has also been detected on peritoneal mast cells, co-localized with CD21/CD35, and it is proposed to play a role in complement-mediated mast-cell activation.