Role and therapeutic efficacy of interleukin-35 in experimental autoimmune encephalomyelitis

Abstract

Multiple Sclerosis (MS) is one of the most prevalent inflammatory demyelinating diseases of the central nervous system (CNS). MS pathological mechanism begins with the escape of myelin-reactive T cells from central tolerance, followed by peripheral activation and CNS infiltration, leading to reactive gliosis, demyelination and axonal injury. Interleukin-35 (IL-35) is an anti-inflammatory cytokines and composes of two subunits: Epstein-Barr virus induced gene 3 (Ebi3) and p35. IL-35 has the potential to ameliorate immune-mediated diseases by suppressing inflammatory lymphocytes and inducing regulatory lymphocytes. With its immunosuppressive property, IL-35 may be a target for the development of novel treatment strategy for MS. I aimed to investigate the role and therapeutic efficacy of IL-35 on experimental autoimmune encephalomyelitis (EAE), an animal model of MS. To understand the role of IL-35 during the course of EAE, EAE was induced in C57BL/6 mice by immumization with MOG35-55 peptides. Mice were sacrificed at 14 days (initial phase), 21 days (progressive phase) and 28 days (recovery phase) after immunization. To investigate whether overexpressing IL-35 affect the pathophysiology of EAE, gene electrotransfer of recombinant IL-35 was conducted in the tibialis anterior muscle of EAE mice at 10 days and 17 days after immunization. Mice were sacrificed at 21 days after immunization. Expression of IL-35 was reduced in the progressive phase of EAE and it was restored in the recovery phase. Along with downregulation of IL-35 in the progressive phase, astrocytes and microglia were robustly activated, and demyelination was found most severe. In contrast, as IL-35 expression level was restored in the recovery phase, astrocytes and microglia were less activated and demyelination was less severe. These results indicated that EAE severity and immune pathology are negatively associated with the expression level of IL-35. Overexpression of IL-35 by gene electrotransfer attenuated EAE severity. Immunofluorescence staining showed an increased level of myelination, associated with reduced level of astrocyte activation and macrophages infiltration. These results reveal that increasing IL-35 expression level by gene electrotransfer can alleviate EAE severity and preserve myelin. Its underlying mechanism is probably through inhibiting astrocyte activation and macrophages infiltration. This study is the first attempt to understand how IL-35 is associated with EAE immunopathology including reactive gliosis, immune cell infiltration and demyelination. This has provided a solid ground for future investigation of the effect of IL-35 on glial cells. Our results indicate that overexpression of IL-35 is an effective strategy for EAE. This study reveals the therapeutic potential of IL-35 as a target for the development of novel treatment for MS.