RESUMEN
Almost four decades of research into the role of human leukocyte antigen-B27 (HLA-B27) in susceptibility to spondyloarthritis has yet to yield a convincing answer. New results from an HLA-B27 transgenic rat model now demonstrate quite convincingly that CD8(+) T cells are not required for the inflammatory phenotype. Discoveries that the HLA-B27 heavy chain has a tendency to misfold during the assembly of class I complexes in the endoplasmic reticulum (ER) and to form aberrant disulfide-linked dimers after transport to the cell surface have forced the generation of new ideas about its role in disease pathogenesis. In transgenic rats, HLA-B27 misfolding generates ER stress and leads to activation of the unfolded protein response, which dramatically enhances the production of interleukin-23 (IL-23) in response to pattern recognition receptor agonists. These findings have led to the discovery of striking T-helper 17 cell activation and expansion in this animal model, consistent with results emerging from humans with spondyloarthritis and the discovery of IL23R as an additional susceptibility gene for ankylosing spondylitis. Together, these results suggest a novel link between HLA-B27 and the T-helper 17 axis through the consequences of protein misfolding and open new avenues of investigation as well as identifying new targets for therapeutic intervention in this group of diseases.
Asunto(s)
Retículo Endoplásmico/inmunología , Antígeno HLA-B27/inmunología , Transducción de Señal/inmunología , Espondiloartritis/inmunología , Respuesta de Proteína Desplegada/inmunología , Animales , Modelos Animales de Enfermedad , Retículo Endoplásmico/metabolismo , Predisposición Genética a la Enfermedad , Antígeno HLA-B27/química , Antígeno HLA-B27/genética , Antígeno HLA-B27/metabolismo , Humanos , Interleucina-23/inmunología , Ratones , Ratones Transgénicos , Pliegue de Proteína , Multimerización de Proteína , Transporte de Proteínas , Ratas , Ratas Transgénicas , Receptores de Interleucina/genética , Receptores de Interleucina/inmunología , Receptores de Reconocimiento de Patrones/inmunología , Factores de Riesgo , Transducción de Señal/genética , Espondiloartritis/genética , Espondiloartritis/metabolismo , Linfocitos T/inmunología , Respuesta de Proteína Desplegada/genéticaRESUMEN
OBJECTIVE: To determine whether HLA-B27 misfolding and the unfolded protein response (UPR) result in cytokine dysregulation and whether this is associated with Th1 and/or Th17 activation in HLA-B27/human beta(2)-microglobulin (Hubeta(2)m)-transgenic rats, an animal model of spondylarthritis. METHODS: Cytokine expression in lipopolysaccharide (LPS)-stimulated macrophages was analyzed in the presence and absence of a UPR induced by chemical agents or by HLA-B27 up-regulation. Cytokine expression in colon tissue and in cells purified from the lamina propria was determined by real-time reverse transcription-polymerase chain reaction analysis, and differences in Th1 and Th17 CD4+ T cell populations were quantified after intracellular cytokine staining. RESULTS: Interleukin-23 (IL-23) was found to be synergistically up-regulated by LPS in macrophages undergoing a UPR induced by pharmacologic agents or by HLA-B27 misfolding. IL-23 was also increased in the colon tissue from B27/Hubeta(2)m-transgenic rats concurrently with the development of intestinal inflammation, and IL-17, a downstream target of IL-23, exhibited robust up-regulation in a similar temporal pattern. IL-23 and IL-17 transcripts were localized to CD11+ antigen-presenting cells and CD4+ T cells, respectively, from the colonic lamina propria. Colitis was associated with a 6-fold expansion of CD4+ IL-17-expressing T cells. CONCLUSION: The IL-23/IL-17 axis is strongly activated in the colon of B27/Hubeta(2)m-transgenic rats with spondylarthritis-like disease. HLA-B27 misfolding and UPR activation in macrophages can result in enhanced induction of the pro-Th17 cytokine IL-23. These results suggest a possible link between HLA-B27 misfolding and immune dysregulation in this animal model, with implications for human disease.
Asunto(s)
Antígeno HLA-B27/química , Antígeno HLA-B27/metabolismo , Interleucina-17/metabolismo , Interleucina-23/metabolismo , Espondiloartritis/metabolismo , Espondiloartritis/patología , Linfocitos T Colaboradores-Inductores/metabolismo , Animales , Células Cultivadas , Colon/metabolismo , Colon/patología , Modelos Animales de Enfermedad , Antígeno HLA-B27/genética , Humanos , Lipopolisacáridos/farmacología , Macrófagos/metabolismo , Macrófagos/patología , Ratones , Ratones Endogámicos C57BL , Conformación Proteica , Ratas , Ratas Endogámicas F344 , Ratas Transgénicas , Linfocitos T Colaboradores-Inductores/patología , Células TH1/metabolismo , Células TH1/patología , Microglobulina beta-2/genética , Microglobulina beta-2/metabolismoRESUMEN
Type I IFN are strongly induced upon engagement of certain pattern recognition receptors by microbial products, and play key roles in regulating innate and adaptive immunity. It has become apparent that the endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR), in addition to restoring ER homeostasis, also influences the expression of certain inflammatory cytokines. However, the extent to which UPR signaling regulates type I IFN remains unclear. Here we show that cells undergoing a UPR respond to TLR4 and TLR3 ligands, and intracellular dsRNA, with log-fold greater IFN-beta induction. This synergy is not dependent on autocrine type I IFN signaling, but unexpectedly requires the UPR transcription factor X-box binding protein 1 (XBP-1). Synergistic IFN-beta induction also occurs in HLA-B27/human beta(2)m-transgenic rat macrophages exhibiting a UPR as a consequence of HLA-B27 up-regulation, where it correlates with activation of XBP-1 splicing. Together these findings indicate that the cellular response to endogenous 'danger' that disrupts ER homeostasis is coupled to IFN-beta induction by XBP-1, which has implications for the immune response and the pathogenesis of diseases involving the UPR.
Asunto(s)
Proteínas de Unión al ADN/fisiología , Retículo Endoplásmico/metabolismo , Interferón beta/metabolismo , Proteínas Nucleares/fisiología , Transducción de Señal/fisiología , Animales , Animales Modificados Genéticamente , Citocinas/metabolismo , Retículo Endoplásmico/efectos de los fármacos , Fibroblastos/citología , Fibroblastos/efectos de los fármacos , Fibroblastos/metabolismo , Expresión Génica/efectos de los fármacos , Antígeno HLA-B27/genética , Antígeno HLA-B7/genética , Humanos , Factor 7 Regulador del Interferón/genética , Interferón-alfa/genética , Interferón beta/química , Interferón beta/genética , Lipopolisacáridos/farmacología , Macrófagos/efectos de los fármacos , Macrófagos/metabolismo , Ratones , Ratones Noqueados , Pliegue de Proteína , ARN Interferente Pequeño/genética , Ratas , Ratas Endogámicas F344 , Receptor de Interferón alfa y beta/genética , Factores de Transcripción del Factor Regulador X , Transducción de Señal/efectos de los fármacos , Tapsigargina/farmacología , Factores de Transcripción , Tunicamicina/farmacología , Proteína 1 de Unión a la X-BoxRESUMEN
OBJECTIVE: HLA-B27 is implicated in the pathogenesis of spondylarthritis (SpA), yet the molecular mechanisms are incompletely defined. HLA-B27 misfolding has been associated with endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in macrophages from HLA-B27/human beta(2)-microglobulin-transgenic (B27-transgenic) rats. This study was performed to assess the mechanisms that drive activation of the HLA-B27-induced UPR and to determine whether splenocytes respond in a similar manner. METHODS: Splenocytes were isolated and bone marrow macrophages were derived from B27-transgenic and wild-type rats. Cells were treated for up to 24 hours with cytokines that induce class I major histocompatibility complex expression. HLA-B27 expression and misfolding were assessed by real-time reverse transcription-polymerase chain reaction, flow cytometry, and immunoblotting. Activation of the UPR was measured by quantifying UPR target gene expression and X-box binding protein 1 messenger RNA (mRNA) splicing. RESULTS: HLA-B27 mRNA up-regulation was accompanied by a dramatic increase in the accumulation of misfolded heavy chains and preceded robust activation of the UPR in macrophages. When macrophages were treated with various cytokines, the magnitude of the UPR correlated strongly with the degree of HLA-B27 up-regulation. In contrast, B27-transgenic splenocytes exhibited only low-level differences in the expression of UPR target genes after exposure to interferon-gamma or concanavalin A, which resulted in minimal HLA-B27 up-regulation. CONCLUSION: These results suggest that HLA-B27-associated activation of the UPR in macrophages is attributable to the accumulation of misfolded heavy chains, and that certain cell types may be more susceptible to the effects of HLA-B27 misfolding. Strategies that eliminate HLA-B27 up-regulation and/or the accumulation of misfolded heavy chains may be useful in evaluating the role of these events in the pathogenesis of SpA.