Methods: Isogenic epithelial cell lines expressing two copies of either HLA-B*27:05 and a control HLA-B*35:01 heavy chain (HC) were generated to determine the effect on the Salmonella infection life-cycle. A cell line expressing HLA-B*27:05.HC physically linked to the light chain beta-2-microglobulin and a specific peptide (referred to as a single chain trimer, SCT) was also generated to determine the effects of HLA-B27 folding status on S. enterica life-cycle. XBP-1 venus and AMP dependent Transcription Factor (ATF6)-FLAG reporters were used to monitor UPR activation in infected cells. Triacin C was used to inhibit de novo lipid synthesis during UPR, and confocal imaging of ER tracker stained membrane allowed quantification of glibenclamide-associated membrane.
Results: S. enterica demonstrated enhanced replication with an altered cellular localisation in the presence of HLA-B*27:05.HC but not in the presence of HLA-B*27:05.SCT or HLA-B*35:01. HLA-B*27:05.HC altered the threshold for UPR induction. Salmonella activated the UPR and required XBP-1 for replication, which was associated with endoreticular membrane expansion and lipid metabolism.
Conclusions: HLA-B27 misfolding and a UPR cellular environment are associated with enhanced Salmonella replication, while Salmonella itself can activate XBP-1 and ATF6. These data provide a potential mechanism linking the life-cycle of Salmonella with the physicochemical properties of HLA-B27 and cellular events that may contribute to ReA pathogenesis. Our observations suggest that the UPR pathway maybe targeted for future therapeutic intervention.