Hye-Lin Ha

Interleukin-17 Cytokines Are Critical in Development of Fatal Lupus Glomerulonephritis

Systemic lupus erythematosus is a potentially fatal autoimmune disease. Although interleukin-17 (IL-17) has been linked to human lupus and mouse models of this disease, it has not been addressed whether this cytokine plays a critical role in fatal lupus pathology. Here we have demonstrated that increased production of IL-17 cytokines and their signaling via the adaptor protein CIKS (a.k.a. Traf3ip2, Act1) critically contributed to lethal pathology in an FcgammaR2b-deficient mouse model of lupus. Mice lacking IL-17 and especially those lacking CIKS showed greatly improved survival and were largely protected from development of glomerulonephritis. Importantly in this model, potential effects of IL-17 cytokines on antibody production could be distinguished from critical local contributions in kidneys, including recruitment of neutrophils and monocytes. These findings provide the proof of principle that signaling by IL-17 family cytokines mediated via CIKS presents promising therapeutic targets for the treatment of systemic lupus erythematosus, especially in cases with kidney involvement.

IL-17 drives psoriatic inflammation via distinct, target cell-specific mechanisms

Significance Psoriasis is an inflammatory disease affecting the skin, a barrier site. The disease is characterized by abnormal growth of keratinocytes and infiltration of inflammatory cells. Clinical trials targeting the IL-17 cytokine have shown remarkable efficacy, and IL-17 also has been strongly implicated in the imiquimod-induced mouse model of psoriasis. However why IL-17 cytokines should be so central is not known, because target cells and their functions have not been clearly delineated. Here we demonstrate that IL-17 signaling into nonkeratinocytes, specifically dermal fibroblasts, induces mediators that further increase IL-17 production by innate γδT cells and promote cellular infiltration, whereas IL-17 signaling into keratinocytes aids proliferation and blocks their differentiation. These findings reveal the circuitry underpinning critical disease-driving effects of IL-17. Psoriasis is a chronic inflammatory skin disease characterized by abnormal keratinocyte proliferation and differentiation and by an influx of inflammatory cells. The mechanisms underlying psoriasis in humans and in mouse models are poorly understood, although evidence strongly points to crucial contributions of IL-17 cytokines, which signal via the obligatory adaptor CIKS/Act1. Here we identify critical roles of CIKS/Act1-mediated signaling in imiquimod-induced psoriatic inflammation, a mouse model that shares features with the human disease. We found that IL-17 cytokines/CIKS-mediated signaling into keratinocytes is essential for neutrophilic microabscess formation and contributes to hyperproliferation and markedly attenuated differentiation of keratinocytes, at least in part via direct effects. In contrast, IL-17 cytokines/CIKS-mediated signaling into nonkeratinocytes, particularly into dermal fibroblasts, promotes cellular infiltration and, importantly, leads to enhanced the accumulation of IL-17–producing γδT cells in skin, comprising a positive feed-forward mechanism. Thus, CIKS-mediated signaling is central in the development of both dermal and epidermal hallmarks of psoriasis, inducing distinct pathologies via target cell-specific effects. CIKS-mediated signaling represents a potential therapeutic target in psoriasis.

CIKS/Act1-Mediated Signaling by IL-17 Cytokines in Context: Implications for How a CIKS Gene Variant May Predispose to Psoriasis

Psoriasis is a relapsing skin disease characterized by abnormal keratinocyte proliferation and differentiation and by an influx of inflammatory immune cells. Recently, IL-17 cytokines have been strongly implicated as critical for the pathogenesis of this disease. IL-17A (also known as IL-17) and IL-17F are the signature cytokines of Th17 cells, but are also produced by innate cells, including γδ T cells present in skin, whereas epithelial cells, including keratinocytes, may produce IL-17C. IL-17 cytokines signal via the adaptor protein connection to IκB kinase and stress-activated protein kinases (CIKS)/Act1. Psoriasis is a disease with a strong genetic predisposition, and the gene encoding CIKS has recently been identified as a susceptibility locus. Unexpectedly, one predisposing gene variant features a mutation that impairs rather than enhances CIKS-mediated IL-17 cytokine signaling, counter to the predicted role for IL-17 cytokines in psoriatic inflammation. In this study, we demonstrate, however, that this mutant adaptor does not impair the IL-17–specific contributions to the genetic response when combined with TNF-α, a cytokine also prominent in psoriatic inflammation. Interestingly, TNF-α signals compensate IL-17 signaling defects imposed by this mutant adaptor even for genes that are not induced by TNF-α alone, including the transcription factors CCAAT/enhancer binding protein δ and IκBζ, which help regulate secondary gene expression in response to IL-17. Based on these findings we discuss a scenario in which the mutant adaptor may interfere with homeostatic maintenance of epithelial barriers, thereby potentially enabling the initiation of inflammatory responses to insults, whereas this same mutant adaptor would still be able to mediate IL-17–specific contributions to inflammation once TNF-α is present.

The Oncoprotein and Transcriptional Regulator Bcl-3 Governs Plasticity and Pathogenicity of Autoimmune T Cells

Bcl-3 is an atypical member of the IκB family that modulates transcription in the nucleus via association with p50 (NF-κB1) or p52 (NF-κB2) homodimers. Despite evidence attesting to the overall physiologic importance of Bcl-3, little is known about its cell-specific functions or mechanisms. Here we demonstrate a T-cell-intrinsic function of Bcl-3 in autoimmunity. Bcl-3-deficient T cells failed to induce disease in T cell transfer-induced colitis and experimental autoimmune encephalomyelitis. The protection against disease correlated with a decrease in Th1 cells that produced the cytokines IFN-γ and GM-CSF and an increase in Th17 cells. Although differentiation into Th1 cells was not impaired in the absence of Bcl-3, differentiated Th1 cells converted to less-pathogenic Th17-like cells, in part via mechanisms involving expression of the RORγt transcription factor. Thus, Bcl-3 constrained Th1 cell plasticity and promoted pathogenicity by blocking conversion to Th17-like cells, revealing a unique type of regulation that shapes adaptive immunity.

The NF-κB regulator Bcl-3 governs dendritic cell antigen presentation functions in adaptive immunity.

Bcl-3 is an atypical member of the IκB family and modulates gene expression via interaction with p50/NF-κB1 or p52/NF-κB2 homodimers. We report in the present study that Bcl-3 is required in dendritic cells (DCs) to assure effective priming of CD4 and CD8 T cells. Lack of Bcl-3 in bone marrow–derived DCs blunted their ability to expand and promote effector functions of T cells upon Ag/adjuvant challenge in vitro and after adoptive transfers in vivo. Importantly, the critical role of Bcl-3 for priming of T cells was exposed upon Ag/adjuvant challenge of mice specifically ablated of Bcl-3 in DCs. Furthermore, Bcl-3 in endogenous DCs was necessary for contact hypersensitivity responses. Bcl-3 modestly aided maturation of DCs, but most consequentially, Bcl-3 promoted their survival, partially inhibiting expression of several antiapoptotic genes. Loss of Bcl-3 accelerated apoptosis of bone marrow–derived DCs during Ag presentation to T cells, and DC survival was markedly impaired in the context of inflammatory conditions in mice specifically lacking Bcl-3 in these cells. Conversely, selective overexpression of Bcl-3 in DCs extended their lifespan in vitro and in vivo, correlating with increased capacity to prime T cells. These results expose a previously unidentified function for Bcl-3 in DC survival and the generation of adaptive immunity.

Cutting Edge: IL-25 Targets Dendritic Cells To Attract IL-9–Producing T Cells in Acute Allergic Lung Inflammation

Asthma is a common inflammatory disease of airways that is often associated with type 2 responses triggered by allergens, such as house dust mites (HDMs). IL-25 is a key mucosal cytokine that may be produced by stressed epithelial cells; it rapidly activates type 2 innate lymphoid cells to produce IL-13 and IL-5. When administered directly into lungs, IL-25 induces acute inflammation. However, the mechanisms underlying IL-25–initiated inflammation and the roles of this cytokine in the context of HDM-induced allergic inflammation are not fully understood. We show in this article that lung-resident conventional dendritic cells were direct targets of IL-25. IL-25–stimulated dendritic cells rapidly induced mediators, such as the chemokine CCL17, which, in turn, attracted IL-9–producing T cells. Importantly, these mechanisms also operated during HDM-induced allergic lung inflammation.

Adaptive immune‐mediated host resistance to Toxoplasma gondii is governed by the NF‐κB regulator Bcl‐3 in dendritic cells

The atypical IκB family member Bcl‐3 associates with p50/NF‐κB1 or p52/NF‐κB2 homodimers in nuclei, thereby either positively or negatively modulating transcription in a context‐dependent manner. Previously we reported that Bcl‐3 was critical for host resistance to Toxoplasma gondii. Bcl‐3‐deficient mice succumbed within 3–5 weeks after infection, correlating with an apparently impaired Th1‐type adaptive immune response. However in which cell type(s) Bcl‐3 functioned to assure resistance remained unknown. We now show that Bcl‐3 expression in dendritic cells is required to generate a protective Th1‐type immune response and confer resistance to T. gondii. Surprisingly, mice lacking Bcl‐3 in dendritic cells were as susceptible as mice globally deficient for Bcl‐3. Furthermore, early innate defenses were not compromised by the absence of Bcl‐3, as initial production of IL‐12 by dendritic cells and IFN‐γ by NK cells were preserved. However, subsequent production of IFN‐γ by CD4+ and CD8+ T‐cells was compromised when dendritic cells lacked Bcl‐3, and these mice succumbed at a time when T‐cell‐mediated IFN‐γ production was essential for host resistance. These findings demonstrate that Bcl‐3 is required in dendritic cells to prime protective T‐cell‐mediated immunity to T. gondii.