Chemokine receptors are a family of receptors that signal upon binding of one or more members of the chemokine superfamily of chemotactic cytokines. Chemokines coordinate development, differentiation and trafficking of various immune system cells making them key players of the innate and adaptive immune response.

CXCR5 (also known as Burkitt lymphoma receptor 1) belongs to the CXC subfamily of chemokine receptors and is a G-coupled protein receptor with 7 transmembrane segments. There is considerable homology between CXCR5 and other members of the chemokine receptor family such as IL-9 receptor, CCR-1 and BLR2. CXCR5 expression is detected in peripheral blood CD4 and CD8 leukocytes as well as in secondary lymphatic organs and in granule and Purkinje layers in the brain. It is also expressed in Burkitt’s lymphoma cells¹.

CXCR5 is activated by B-cell attracting chemokine 1 (BCA-1) that is chemotactic for human B lymphocytes. BCA-1 does not affect IL-2 stimulated T-cells, monocytes or neutrophils². CXCR5 mediates correct T cell localization within granulomas, efficient macrophage activation and lymphoid follicle formation³.

CXCR5 knockout mice have a severe defect in normal B cell migration and localization. Knockout mice lack inguinal lymph nodes, have a reduced amount of Peyer’s patches and have abnormal primary lymphoid follicles and no functional germinal centers in the spleen⁴. Absence of CXCR5 has been implicated in increased susceptibility to tuberculosis to due defective T cell localization within the lung³.