Tetramerization of Transcription Factor STAT5 in Monocytes Promotes Autoimmune-mediated Neuroinflammation via the Regulation of CCL17

STAT5 plays a critical role in mediating cellular responses following cytokine stimulation. The activated STAT5 proteins can form dimers and tetramers with distinct biological functions. The role of STAT5 tetramerization in autoimmune-mediated neuroinflammation has not been investigated. Using the STAT5 tetramer-deficient Stat5a-Stat5b N-domain double knock-in (DKI) mouse strain, we report here that STAT5 tetramers promote the pathogenesis of experimental autoimmune encephalomyelitis (EAE). The mild EAE phenotype observed in DKI mice correlates with the impaired extravasation of pathogenic Th17 cells and interactions between Th17 cells and monocyte-derived cells (MDCs) in the meninges. We further demonstrated that STAT5 tetramerization regulates the GM-CSF-dependent production of CCL17 by MDCs. Importantly, DKI Th17 cells expanded with CCL17 exhibit more severe EAE. Mechanistically, the effect of CCL17 is dependent on the activity of the integrin VLA-4. Thus, our study uncovered a novel GM-CSF-STAT5 tetramer-CCL17 pathway that promotes autoimmune neuroinflammation via the regulation of Th17 cell migration. For isolating monoyctes and monoycte-derived APCs from the mice, EAE was induced in STAT5 tetramer-deficient (DKI) mice by active immunization with MOG35-55 in CFA and pertussis toxin. Bone marronw monocytes, and spinal cord monocytes, and spinal cord APCs were isolated on day 14 after immunization by cell sorting. For the isolation of pathogenic Th17 cells, WT and DKI mice were immunized with MOG35-55 in CFA without pertussis toxin administration. Cells from the spleens and lymph nodes were isolated on day 14 following immunization and expanded with MOG35-55 peptide under Th17 conditions, with or without the addition of CCL17. CD4+ T cells were isolated 3 days following expansion by cell sorting.