CD4 T cell-intrinsic role for the T helper 17 signature cytokine IL-17: Effector resistance to immune suppression

• Published in: Proceedings of the National Academy of Sciences - PNAS 2020-08, Vol.117 (32), p.19408-19414
• Main Authors: Crawford, Michael P., Sinha, Sushmita, Renavikar, Pranav S., Borcherding, Nicholas, Karandikar, Nitin J.
• Format: Article
• Language: English
• Subjects: Adenomatous polyposis coli; Antigen-presenting cells; Arthritis; Autoimmune diseases; Biological Sciences; CD4 antigen; CD4-Positive T-Lymphocytes - immunology; CD8 antigen; CD8-Positive T-Lymphocytes - immunology; Cell Differentiation; Cytokines; Effector cells; Helper cells; Humans; IL-1β; Immune Tolerance - immunology; Inflammatory bowel diseases; Interleukin 17; Interleukin 6; Interleukin-17 - immunology; Interleukin-17 - metabolism; Interleukin-1beta - metabolism; Interleukin-6 - metabolism; Intestine; Lymphocytes; Lymphocytes T; Multiple sclerosis; Pathogenesis; Psoriasis; Regulatory mechanisms (biology); Signal Transduction; Stat3 protein; STAT3 Transcription Factor - metabolism; T-Lymphocyte Subsets - immunology; Th17 Cells - immunology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2005010117

Untoward effector CD4+ T cell responses are kept in check by immune regulatory mechanisms mediated by CD4+ and CD8+ T cells. CD4+ T helper 17 (Th17) cells, characterized by IL-17 production, play important roles in the pathogenesis of autoimmune diseases (such as arthritis, multiple sclerosis, psoriasis, inflammatory bowel disease, among others) and in the host response to infection and cancer. Here, we demonstrate that human CD4+ T cells cells exposed to a Th17-differentiating milieu are significantly more resistant to immune suppression by CD8+ T cells compared to control Th0 cells. This resistance is mediated, in part, through the action of IL-17A, IL-17F, and IL-17AF heterodimer through their receptors (IL-17RA and IL-17RC) on CD4+ T cells themselves, but not through their action on CD8+ T cells or APC. We further show that IL-17 can directly act on non-Th17 effector CD4+ T cells to induce suppressive resistance, and this resistance can be reversed by blockade of IL-1β, IL-6, or STAT3. These studies reveal a role for IL-17 cytokines in mediating CD4-intrinsic immune resistance. The pathways induced in this process may serve as a critical target for future investigation and immunotherapeutic intervention.