Type I Interferon–Activated STAT4 Regulation of Follicular Helper T Cell–Dependent Cytokine and Immunoglobulin Production in Lupus

Abstract

Objective. To assess the role of STAT4 activation in driving pathogenic follicular helper T (Tfh) cell secretion of the cytokines interleukin-21 (IL-21) and interferon-γ (IFNγ) in murine and human lupus. Methods. The effect of STAT4-dependent Tfh cell signaling on cytokine production and autoreactive B cell maturation was assessed temporally during the course of lupus in a murine model, with further assessment of Tfh cell gene transcription performed using RNA-Seq technology. STAT4-dependent signaling and cytokine production were also determined in circulating Tfh-like cells in patients with systemic lupus erythematosus (SLE), as compared to cells from healthy control subjects, and correlations with disease activity were assessed in the Tfh-like cells from SLE patients. Results. IL-21-and IFNγ-coproducing Tfh cells expanded prior to the detection of potentially pathogenic IgG2c autoantibodies in lupus-prone mice. Tfh cells transcriptionally evolved during the course of disease with acquisition of a STAT4-dependent gene signature. Maintenance of Tfh cell cytokine synthesis was dependent upon STAT4 signaling, driven by type I IFNs. Circulating Tfh-like cells from patients with SLE also secreted IL-21 and IFNγ, with STAT4 phosphorylation enhanced by IFNβ, in association with the extent of clinical disease activity. Conclusion. We identified a role for type I IFN signaling in driving STAT4 activation and production of IL-21 and IFNγ by Tfh cells in murine and human lupus. Enhanced STAT4 activation in Tfh cells may underlie pathogenic B cell responses in both murine and human lupus. These data indicate that STAT4 guides pathogenic cytokine and immunoglobulin production in SLE, demonstrating a potential therapeutic target to modulate autoimmunity.

Reply

“…Nevertheless, their conclusion that Tfh cell production of IL-21, IFNγ, and immunoglobulin is dependent on type I IFN-activated STAT4 regulation of Tfh cells may be exaggerated and possibly even misleading. (3). Furthermore, as disease progressed, transcriptional analysis revealed that Tfh cells up-regulated type I IFN-driven gene transcription and acquired an enhanced STAT4 gene signature (3).…”

“…We found that although coproduction of IL‐21 and IFNγ is maintained in Tfh cells in lupus despite progressive loss of Bcl6 and T‐bet expression, phosphorylation of STAT4 continued to increase upon type I IFN stimulation (3). Furthermore, as disease progressed, transcriptional analysis revealed that Tfh cells up‐regulated type I IFN–driven gene transcription and acquired an enhanced STAT4 gene signature (3). STAT4 binds and promotes the regulation of IL21 and Ifng during CD4 T cell differentiation (4).…”

“…Anti–IFNAR‐1 blockade reduced Tfh cell percentages and numbers, but they were not ablated (3). Despite the reduced numbers of Tfh cells and altered cytokine profiles, the persistence of germinal centers (GCs) and IgG1 isotype autoantibodies after treatment substantiates the idea that these cells still function in the ongoing GC response (3) characteristic of lupus. While IgG2c autoantibodies were still produced, these were likely generated by existing plasma cells or those reliant on Tfh cells that retained their IFNγ production after treatment.…”

“…STAT4 binds and promotes the regulation of IL21 and Ifng during CD4 T cell differentiation (4). We went on to demonstrate, using an assay for transposase‐accessible chromatin with sequencing analysis of Tfh cells after in vivo blockade of type I IFN in lupus‐prone mice, that the IL21 and Ifng loci remain accessible in the absence of type I IFN signaling, yet IL‐21 and IFNγ production was reduced (3). This suggested that in the absence of type I IFN, STAT4 could not be activated and bind to these open loci to maintain Tfh cell cytokine production.…”

Understanding the Relationships Between Type I Interferon, STAT4, and the Production of Interleukin‐21 and Interferon‐γ by Follicular Helper T Cells in Lupus: Comment on the Article by Dong et al

“…Second, Dong and colleagues found that IFNβ can promote more significant phosphorylation of STAT4 in splenic Tfh cells and Th1 cells at a later stage of disease compared to the predisease stage (8). However, we wonder why the authors did not further investigate the role of IFNβ in regulating IL‐21 and IFNγ production by splenic Tfh cells and Th1 cells by direct stimulation with IFNβ.…”