GPR183

Abstract: The EBI2 receptor (Epstein–Barr virus-induced gene 2, also known as GPR183) was recently shown to be linked to autoimmune disease, and is a critical regulator of the humoral immune response. It is a G-protein-coupled receptor, and its natural ligand has been unknown. Two groups now bring an end to the 'orphan' status of this receptor with identification of specific oxysterols as its natural ligands. The most potent ligand and activator is 7a,25-dihydroxycholesterol, and the EBI2–oxysterol signalling pathway has an important role in the adaptive immune response. EBI2 (also called GPR183) is an orphan G-protein-coupled receptor that is highly expressed in spleen and upregulated upon Epstein–Barr-virus infection1. Recent studies indicated that this receptor controls follicular B-cell migration and T-cell-dependent antibody production2,3,4,5,6. Oxysterols elicit profound effects on immune and inflammatory responses as well as on cholesterol metabolism7,8,9. The biological effects of oxysterols have largely been credited to the activation of nuclear hormone receptors10,11. Here we isolate oxysterols from porcine spleen extracts and show that they are endogenous ligands for EBI2. The most potent ligand and activator is 7α,25-dihydroxycholesterol (OHC), with a dissociation constant of 450 pM for EBI2. In vitro, 7α,25-OHC stimulated the migration of EBI2-expressing mouse B and T cells with half-maximum effective concentration values around 500 pM, but had no effect on EBI2-deficient cells. In vivo, EBI2-deficient B cells or normal B cells desensitized by 7α,25-OHC pre-treatment showed reduced homing to follicular areas of the spleen. Blocking the synthesis of 7α,25-OHC in vivo with clotrimazole, a CYP7B1 inhibitor, reduced the content of 7α,25-OHC in the mouse spleen and promoted the migration of adoptively transferred pre-activated B cells to the T/B boundary (the boundary between the T-zone and B-zone in the spleen follicle), mimicking the phenotype of pre-activated B cells from EBI2-deficient mice. Our results show an unexpected causal link between EBI2, an orphan G-protein-coupled receptor controlling B-cell migration, and the known immunological effects of certain oxysterols, thus uncovering a previously unknown role for this class of molecules.

Abstract: The correct positioning of B cells within lymphoid follicles is critical for mounting antibody responses, and positioning of activated B cells in interfollicular regions and in the outer follicle is also thought to be important for supporting normal interactions between T cells and B cells and normal B-cell proliferation. The molecular cues controlling these positioning events have been unknown. Pereira et al. now establish that EBI2, an orphan G-protein-coupled receptor upregulated by Epstein–Barr virus infection, promotes B-cell positioning in the outer follicle. By down-regulating EBI2, germinal centre B cells are able to move to the follicle centre. Mice lacking or mis-expressing this receptor are shown to mount defective antibody responses. B cells migrate to the outer or centre lymphoid follicle at different stages of antibody responses. Here it is shown that activated B cells must downregulate the orphan G protein-coupled receptor EBI2 to migrate to the centre follicles, where they mount T dependent antibody responses and establish germinal centres. B cell follicles are specialized microenvironments that support events necessary for humoral immunity1,2,3. After antigen encounter, activated B cells initially seek T-cell help at the follicle–T-zone boundary and then move to interfollicular and T-zone distal (outer) regions of the follicle4,5,6,7,8,9,10. Subsequently, some cells move to the follicle centre, become germinal centre B cells and undergo antibody affinity maturation1,2,11. Although germinal centres within follicles were described in 1885 (ref. 12), the molecular cues mediating segregation of B cells between the outer and centre follicle have remained undefined. Here we present a role for the orphan G-protein-coupled receptor, Epstein-Barr virus induced molecule-2 (EBI2, also known as GPR183)13, in this process. EBI2 is expressed in mature B cells and increases in expression early after activation, before being downregulated in germinal centre B cells. EBI2 deficiency in mice led to a reduction in the early antibody response to a T-dependent antigen. EBI2-deficient B cells failed to move to the outer follicle at day 2 of activation, and instead were found in the follicle centre, whereas EBI2 overexpression was sufficient to promote B cell localization to the outer follicle. In mixed bone marrow chimaeras, EBI2-deficient B cells phenocopied germinal centre B cells in preferentially localizing to the follicle centre. When downregulation of EBI2 in wild-type B cells was antagonized, participation in the germinal centre reaction was impaired. These studies identify an important role for EBI2 in promoting B cell localization in the outer follicle, and show that differential expression of this receptor helps position B cells appropriately for mounting T-dependent antibody responses.