The Immunomodulatory Drug FTY720 Prevents Clearance of Citrobacter rodentium Infection in Mice

Background: The novel immunomodulatory drug, FTY720, blocks the binding of sphingosine- 1-phosphate (S1P) to four of its five G-protein coupled receptors (GPCRs), namely S1P1, S1P3, S1P4 and S1P5, thus preventing lymphocyte migration to sites of inflammation by trapping them within the peripheral lymph nodes, the mesenteric lymph nodes (MLNs) and Peyer's patches. FTY720 has shown great efficacy in both animal models of autoimmunity and human clinical trials and has recently been approved as a first line therapy for multiple sclerosis (MS). However, its clinical use may increase the risk of opportunistic infections, particularly in the gastrointestinal tract. Aims: In this study, we investigated the impact of FTY720 treatment on an infectious model of colitis, using the enteric pathogen Citrobacter rodentium. Methods: Mice were orally gavaged with vehicle or 3mg/kg FTY720 for 6 days pre-infection. Mice continued to receive vehicle or FTY720 every 2nd day up until day 12 (D12) post-infection. Mice were culled at peak-infection, D8 and at D14 i.e. late infection/ clearance. Throughout the study faeces was collected and viable counts enumerated. At necropsy, immune cell phenotyping was carried out on cardiac blood by FACS analysis. C. rodentium colonisation was detected using bioluminescent imaging of whole body and ex vivo organs. Colons were weighed and measured and samples were taken for qRT-PCR and immunoflourescent staining. In addition, splenic colony-forming unit (CFU) counts were enumerated and MLNs were taken for immunoflourescent staining. Results: FACS analysis confirmed peripheral blood lymphopenia in FTY720-treated animals with reduced number of T-cells and increased numbers of dendritic cells. Faecal and splenic CFU counts and bioluminescent imaging revealed an inability of the FTY720-treated mice to clear the infection by D14 in comparison to vehicle-treated animals. These results were supported by clinical and histological signs of colonic inflammation. Gene expression analysis revealed a deficient host immune response in drug treated mice evidenced by increased expression of IL-17A and IL-1β and reduced expression of IL-22. Conclusion: Treatment with the immunomodulatory drug, FTY720, prevents clearance of bacterial infection in the gastrointestinal tract suggesting that continuous treatment with FTY720 impairs the mucosal immune response.