SIGIRR deficiency contributes to CD4 T cell abnormalities by facilitating the IL1/C/EBPß/TNF-α signaling axis in rheumatoid arthritis.

BACKGROUND: Rheumatoid arthritis (RA) is a complex autoimmune disease with multiple etiological factors, among which aberrant memory CD4 T cells activation plays a key role in the initiation and perpetuation of the disease. SIGIRR (single immunoglobulin IL-1R-related receptor), a member of the IL-1 receptor (ILR) family, acts as a negative regulator of ILR and Toll-like receptor (TLR) downstream signaling pathways and inflammation. The aim of this study was to investigate the potential roles of SIGIRR on memory CD4 T cells in RA and the underlying cellular and molecular mechanisms. METHODS: Single-cell transcriptomics and bulk RNA sequencing data were integrated to predict SIGIRR gene distribution on different immune cell types of human PBMCs. Flow cytometry was employed to determine the differential expression of SIGIRR on memory CD4 T cells between the healthy and RA cohorts. A Spearman correlation study was used to determine the relationship between the percentage of SIGIRR+ memory CD4 T cells and RA disease activity. An AIA mouse model (antigen-induced arthritis) and CD4 T cells transfer experiments were performed to investigate the effect of SIGIRR deficiency on the development of arthritis in vivo. Overexpression of SIGIRR in memory CD4 T cells derived from human PBMCs or mouse spleens was utilized to confirm the roles of SIGIRR in the intracellular cytokine production of memory CD4 T cells. Immunoblots and RNA interference were employed to understand the molecular mechanism by which SIGIRR regulates TNF-α production in CD4 T cells. RESULTS: SIGIRR was preferentially distributed by human memory CD4 T cells, as revealed by single-cell RNA sequencing. SIGIRR expression was substantially reduced in RA patient-derived memory CD4 T cells, which was inversely associated with RA disease activity and related to enhanced TNF-α production. SIGIRR-deficient mice were more susceptible to antigen-induced arthritis (AIA), which was attributed to unleashed TNF-α production in memory CD4 T cells, confirmed by decreased TNF-α production resulting from ectopic expression of SIGIRR. Mechanistically, SIGIRR regulates the IL-1/C/EBPß/TNF-α signaling axis, as established by experimental evidence and cis-acting factor bioinformatics analysis. CONCLUSION: Taken together, SIGIRR deficiency in memory CD4 T cells in RA raises the possibility that receptor induction can target key abnormalities in T cells and represents a potentially novel strategy for immunomodulatory therapy.

Analysis of Granulocyte-Macrophage Colony-Stimulating Factor-Producing T Helper Cells in a Mouse Model of Contact Hypersensitivity.

Parallel to traditional Th1/Th2/Th17/Treg lineages, granulocyte-macrophage colony-stimulating factor-producing T helper (Th-GM) cells have been identified as a distinct subset of T helper cells (GM-CSF+ IFN-γ- IL-17A- IL-22- effector CD4+ T cells) in human and mice. Contact hypersensitivity (CHS) is considered an excellent animal model for allergic contact dermatitis (ACD) in human, manifesting an intact T cell-mediated immune response. To provide a standardized and comprehensive assay to analyze the Th-GM cell subset in the T cell-dependent immune response in vivo, a murine CHS model was induced by sensitization/challenge with a reactive, low-molecular-weight, organic hapten, 2,4-dinitrofluorobenzene (DNFB). The Th-GM subset in effector CD4+ T cells generated upon immunization with the hapten was analyzed by flow cytometry. We found that Th-GM was mainly expanded in lesions and draining lymph nodes in the DNFB-induced CHS mouse model. This method can be applied to further study the biology of Th-GM cells and pharmacological research of therapeutic strategies centered on GM-CSF in various conditions, such as ACD.