CXCL13/BLC/BCA-1 is a constitutively expressed chemokine that plays an important role in B and T cell homing. It is expressed by salivary gland epithelium, dendritic cells, osteoclasts, and peritoneal macrophages. It can form homodimers or heterodimers with FGF basic, and it signals through CXCR3 or CXCR5. CXCL13 induces the migration of naive B cells and a subset of memory T cells to lymphoid tissue. It also promotes B1 cell migration into the omentum and peritoneum. In the fetus, CXCL13 attracts CD4+ CD3- IL-7 R alpha+ hematopoietic cells to sites of future Peyer's patch development.