Distinct oxysterol requirements for positioning naïve and activated dendritic cells in the spleen

Correct positioning of dendritic cells (DCs) is critical for efficient pathogen encounter and antigen presentation. Epstein-Barr virus-induced gene 2 (EBI2) has been identified as a chemoattractant receptor required for naïve CD4⁺DCIR2⁺ DC positioning in response to 7α,25-hydroxycholesterol (7α,25-HC). We now provide evidence that a second EBI2 ligand, 7α,27-HC, is involved in splenic DCIR2⁺ DC positioning and homeostasis. Cyp27a1, the enzyme uniquely required for 7α,27-HC synthesis, is expressed by stromal cells in the region of naïve DC localization. After activation, DCIR2⁺ DCs move into the T cell zone. We find that EBI2 is rapidly up-regulated in DCIR2⁺ DCs under certain activation conditions, and positioning at the B-T zone interface depends on EBI2. Under conditions of type I interferon induction, EBI2 ligand levels are elevated, causing activated DCIR2⁺ DCs to disperse throughout the T zone. Last, we provide evidence that oxysterol metabolism by Batf3-dependent DCs is important for EBI2-dependent positioning of activated DCIR2⁺ DCs. This work indicates that 7α,27-HC functions as a guidance cue in vivo and reveals a multitiered role for EBI2 in DC positioning. Deficiency in this organizing system results in defective CD4⁺ T cell responses.