BCA-1 is a CXC chemokine that is highly expressed in thesecondary lymphoid organs， such as follicles of the spleen， lymph nodes， and Peyer’s patches. CXCL13 promotes the migration of B lymphocytes （compared to T cells and macrophages）， by stimulating calcium influx into， and chemotaxis of， cells expressing Burkitt’s lymphoma receptor 1 （BLR1）. BCA1 therefore function in the homing of B lymphocytes to follicles. Human BCA-1 shares a 64% amino acid sequence similarity with the mouse protein and 23 - 34% amino acid sequence identity with other known CXC chemokines. Recombinant or chemically synthesized BCA1 is a potent chemoattractant for B lymphocytes but not T lymphocytes， monocytes or neutrophils. BLR1， a G protein-coupled receptor originally isolated from Burkitt’s lymphoma cells， has now been shown to be the specific receptor for BCA1. Among cells of the hematopoietic lineages， the expression of BLR-1， now designated CXCR-5， is restricted to B lymphocytes and a subpopulation of T helper memory cells.
