Breakdown of blood-brain barrier (BBB), which strictly regulates the entry of immunoglobulin (IgG) and lymphocyte into the central nervous system, is essential to pathogenesis in autoimmune encephalomyelitis such as multiple sclerosis and neuromyelitis optica spectrum disorder (NMOSD). IL-6 increases in serum and cerebrospinal fluid (CSF) in NMOSD patients and its level has been reported to correlate with CSF/serum ratio of albumin, a surrogate marker of BBB function. It is possible that IL-6 are involved in pathogenesis of NMOSD in terms of T and B cells, but roles of IL-6 signal inhibition on BBB function remain unknown.
In this study, we examined the effects of anti-IL-6 receptor antibody on BBB function in EAE mice as a CNS autoimmune disease model in which IL-6 concentration in the CNS dramatically increases.
EAE was induced in female C57BL/6J mice by immunization with myelin oligodendrocyte glycoprotein 35–55 emulsified in adjuvant (Day 0). Pertussis toxin was administered at Days 0 and 2. Control mice were treated with complete Freund's adjuvant and saline alone. Mice were sequentially scored for clinical symptoms of EAE. Anti-IL-6 receptor antibody was intraperitoneally administered on Day 7. On Day 15 or 16, spinal cord, spleen and serum were harvested for immunohistochemistry, flow cytometry and transendothelial electrical resistance (TEER) studies.
Immunohistochemical analysis showed that leakages of albumin and IgG into the spinal cord, which mean BBB permeability, in vehicle-treated EAE mice were higher than those in control mice. The number of CD4-positive T cells also markedly increased in the spinal cord of vehicle-treated EAE mice. Anti-IL-6 receptor antibody significantly reduced those changes in accordance with the prevention of clinical symptoms in EAE mice. It seems that these effects of anti-IL-6 receptor antibody are not only dependent on the inhibition of immune response because anti-IL-6 receptor antibody did not affect T cell differentiation in splenocytes of EAE mice. In addition, the serum of vehicle-treated EAE mice significantly decreased endothelial TEER value of cultured mouse primary endothelial cells, an indicator of permeability, and anti-IL-6 receptor antibody significantly prevented it in vitro.
These results suggest that anti-IL-6 receptor antibody can inhibit the BBB breakdown at least partly by direct effect on the endothelial permeability in EAE mice.