Human blood sample collection and T cell isolation

We recruited healthy donors at UCLA immune assessment core, and collected blood samples according to an IRB protocol approved by the institutional review committee of University of California, Los Angeles (Protocol # 10-001689). Human CD4+ T cells were isolated using Rosettesep Human CD4+ T cell enrichment cocktails (StemCell™ technology) following manufacturer’s instructions. Purified CD4+ T cells were confirmed to be > 95% pure by flow cytometry and the T cell subset composition was monitored (Supplementary Figure 1). We cultured T cells with soluble anti-CD28 (0.2 ug/ml) antibodies on 96-well plates pre-coated with anti-CD3 antibodies (1ug/ml). Interleukin 2 (IL-2) was added at 4.8 U/ml (2 ng/ml). We induced Th17 differentiation with 50 ng/ml IL-6, 50 ng/ml IL-1β and 50 ng/ml IL-23 ³³. We refed T cells at day 7 with medium containing the same Th17 polarizing cytokines and further cultured for another 7 days. We collected supernatants for multiplex Luminex cytokine analysis, and analyzed T cells by intracellular flow cytometry.