EBI2 regulates CXCL13‐mediated responses by heterodimerization with CXCR5

B‐cell movement into lymphoid follicles depends on the expression of the chemokine receptor CXCR5 and the recently reported Epstein‐Barr virus‐induced receptor 2 (EBI2). In cooperation with CXCR5, EBI2 helps to position activated B cells in the follicle, although the mechanism is poorly understood. Using human HEK293T cells and fluorescence resonance energy transfer (FRET) techniques, we demonstrate that CXCR5 and EBI2 form homo‐ and heterodimers. EBI2 expression modulated CXCR5 homodimeric complexes, as indicated by the FRET50 value (CXCR5 homodimer, 0.9851±0.0784; CXCR5 homodimer+EBI2, 1.7320±0.4905; P<0.05). HEK293T cells expressing CXCR5/EBI2 and primary activated murine B cells both down‐modulated CXCR5‐mediated responses, such as Ca2+ flux, cell migration, and MAPK activation; this modulation did not occur when primary B cells were obtained from EBI2–/– mice. The mechanism involves a reduction in binding affinity of the ligand (CXCL13) for CXCR5 (KD: 5.05×10–8 M for CXCR5 alone vs. 1.49×10–7 M for CXCR5/EBI2) and in the efficacy (Emax) of G‐protein activation in CXCR5/EBI2‐coexpressing cells (42.33±4.3%; P<0.05). These findings identify CXCR5/EBI2 heterodimers as functional units that contribute to the plasticity of CXCL13‐mediated B‐cell responses.—Barroso, R., Muñoz, L. Martínez., Barrondo, S., Vega, B., Holgado, B. L., Lucas, P., Baíllo, A., Sallés, J., Rodríguez‐Frade J. M., Mellado, M. EBI2 regulates CXCL13‐mediated responses by heterodimerization with CXCR5. FASEB J. 26, 4841–4854 (2012). www.fasebj.org