2014 Joint ACTRIMS-ECTRIMS Meeting (MSBoston 2014): Oral Presentations

Background: It is well established that TH17 lymphocytes are crucial in the pathogenesis of the chronic autoimmune disease multiple sclerosis (MS). However, the importance of IL-17 in MS is still under debate, and other TH17-associated cytokines are likely more crucial in the initiation and maintenance of neuroinflammation. Objectives: In this study, we addressed the function of IL-26 and its role as TH17-associated cytokine in blood brain barrier (BBB) breakdown and neuroinflammation. Methods: To establish that IL-26 is a TH17-associated cytokine, qPCR for IL-26 and established TH17 markers was performed on differentiated TH17 cells. The expression of IL-26 was confirmed by western blot (WB) and immunohistofluorescence (IHF). ELISA was used to determine expression of IL-26 in serum and cerebrospinal fluid (CSF) of MS patients and controls, and to analyze supernatant of human blood brain barrier endothelial cells (BBBECs) after IL-26 treatment. Expression of the IL-26R (IL-10Rbeta/ IL-20Ralpha) and tight junction proteins on BBB-ECs was analyzed using WB and IHF. Permeability of BBB-EC monolayers after IL-26 treatment was assessed using dextran and BSA diffusion assays. In vivo permeability after i.p. IL-26 treatment of C57Bl/6 mice was assessed by IHF (Evans Blue, fibrinogen and ICAM-1) and 2-photon microscopy (fluorescent dextran). Results: We demonstrate that IL-26 is specifically produced by human TH17 lymphocytes and that it correlates strongly to other TH17-associated markers. IL-26 is increased in the serum and CSF of untreated MS patients, as compared to controls or to treated MS patients. Human BBB-ECs express a functional IL-26R both in vitro and in situ, since they respond to IL-26 treatment by secreting IL-8 and IP-10. IL-26 treatment of BBB-EC monolayers increases their permeability and decreases expression of the tight junction molecule occludin. In vivo, IL-26 treatment increases Evans Blue extravasation in the CNS. Furthermore, we find a significant perivascular accumulation of fibrinogen 2 to 8 hours after IL-26 injection, an upregulation of ICAM-1 on the surface of BBB-ECs, and perivascular accumulation of immune cells in the CNS. This was confirmed by in vivo two-photon microscopy, showing leakage of fluorescent dextran after injection of IL-26. Conclusions: Taken together, these data strongly suggest that IL-26 i) is a TH17-associated cytokine, ii) is correlated to MS disease activity and iii) increases BBB permeability and transmigration of TH lymphocytes, and possibly other immune cells.