SerpinB1 Deficiency Ameliorates Experimental Autoimmune Encephalomyelitis

Abstract

Abstract Increasing evidence shows that, in autoimmune settings, Th17 cells are converted to pathogenic Th17 cells (patho-Th17), which produce GM-CSF and IFNγ and are pivotal for pathogenesis. We recently discovered that serpinB1, a protease inhibitor, is the signature gene of Th17 cells and forms a regulatory module with cathepsin L that controls Th17 cell generation: Th17 differentiation is restricted by serpinB1 and counter-regulated by cathepsin L. In the current study, we investigated serpinB1 regulation of Th17 cell pathogenicity in experimental autoimmune encephalomyelitis (EAE). As anticipated, expression of serpinB1 and other Th17 genes were significantly increased in effector CD4 cells in the EAE mouse. Surprisingly, serpinB1 deficient (sb1−/−) mice immunized with MOG35–55 are resistant to EAE, manifested by dramatically decreased disease incidence and severity. Adoptive transfer experiments showed that the protective effect of serpinB1 deficiency is CD4 cell specific. Cytokine profiling showed that, despite producing more Th17 cells, serpinB1 deficiency selectively diminished patho-Th17 cells. Furthermore, Ki-67 and Annexin V staining together with BrdU pulse/chase strategy confirmed that proliferation is not defective in sb1−/− Th17 and patho-Th17 cells. In contrast, sb1−/− patho-Th17 cells showed significantly shortened life span and were eliminated upon antigen-recall. Finally, in vivo administration of E64D, a broad-acting cysteine protease inhibitor, partially reversed the effects of serpinB1 deficiency. Thus, our study identified a protease-protease inhibitor regulatory module acting on Th17 cell differentiation and separately on pathogenicity with potential for targeting in autoimmune diseases.