Robert A. Colbert

Evolution and transmission of stable CTL escape mutations in HIV infection

Increasing evidence indicates that potent anti-HIV-1 activity is mediated by cytotoxic T lymphocytes (CTLs); however, the effects of this immune pressure on viral transmission and evolution have not been determined. Here we investigate mother–child transmission in the setting of human leukocyte antigen (HLA)-B27 expression, selected for analysis because it is associated with prolonged immune containment in adult infection. In adults, mutations in a dominant and highly conserved B27-restricted Gag CTL epitope lead to loss of recognition and disease progression. In mothers expressing HLA-B27 who transmit HIV-1 perinatally, we document transmission of viruses encoding CTL escape variants in this dominant Gag epitope that no longer bind to B27. Their infected infants target an otherwise subdominant B27-restricted epitope and fail to contain HIV replication. These CTL escape variants remain stable without reversion in the absence of the evolutionary pressure that originally selected the mutation. These data suggest that CTL escape mutations in epitopes associated with suppression of viraemia will accumulate as the epidemic progresses, and therefore have important implications for vaccine design.

HLA–B27 misfolding and the unfolded protein response augment interleukin-23 production and are associated with Th17 activation in transgenic rats

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.

HLA-B27 Misfolding in Transgenic Rats Is Associated with Activation of the Unfolded Protein Response

The mechanism by which the MHC class I allele, HLA-B27, contributes to spondyloarthritis pathogenesis is unknown. In contrast to other alleles that have been examined, HLA-B27 has a tendency to form high m.w. disulfide-linked H chain complexes in the endoplasmic reticulum (ER), bind the ER chaperone BiP/Grp78, and undergo ER-associated degradation. These aberrant characteristics have provided biochemical evidence that HLA-B27 is prone to misfold. Recently, similar biochemical characteristics of HLA-B27 were reported in cells from HLA-B27/human β2-microglobulin transgenic (HLA-B27 transgenic) rats, an animal model of spondyloarthritis, and correlated with disease susceptibility. In this study, we demonstrate that the unfolded protein response (UPR) is activated in macrophages derived from the bone marrow of HLA-B27 transgenic rats with inflammatory disease. Microarray analysis of these cells also reveals an IFN response signature. In contrast, macrophages derived from premorbid rats do not exhibit a strong UPR or evidence of IFN exposure. Activation of macrophages from premorbid HLA-B27 transgenic rats with IFN-γ increases HLA-B27 expression and leads to UPR induction, while no UPR is seen in cells from nondisease-prone HLA-B7 transgenic or wild-type (nontransgenic) animals. This is the first demonstration, to our knowledge, that HLA-B27 misfolding is associated with ER stress that results in activation of the UPR. These observations link HLA-B27 expression with biological effects that are independent of immunological recognition, but nevertheless may play an important role in the pathogenesis of inflammatory diseases associated with this MHC class I allele.

Periodic fever, aphthous stomatitis, pharyngitis, and adenitis (PFAPA) is a disorder of innate immunity and Th1 activation responsive to IL-1 blockade

The syndrome of periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) is the most common periodic fever disease in children. However, the pathogenesis is unknown. Using a systems biology approach we analyzed blood samples from PFAPA patients whose genetic testing excluded hereditary periodic fevers (HPFs), and from healthy children and pediatric HPF patients. Gene expression profiling could clearly distinguish PFAPA flares from asymptomatic intervals, HPF flares, and healthy controls. During PFAPA attacks, complement (C1QB, C2, SERPING1), IL-1–related (IL-1B, IL-1RN, CASP1, IL18RAP), and IFN-induced (AIM2, IP-10/CXCL10) genes were significantly overexpressed, but T cell-associated transcripts (CD3, CD8B) were down-regulated. On the protein level, PFAPA flares were accompanied by significantly increased serum levels of chemokines for activated T lymphocytes (IP-10/CXCL10, MIG/CXCL9), G-CSF, and proinflammatory cytokines (IL-18, IL-6). PFAPA flares also manifested a relative lymphopenia. Activated CD4+/CD25+ T-lymphocyte counts correlated negatively with serum concentrations of IP-10/CXCL10, whereas CD4+/HLA-DR+ T lymphocyte counts correlated positively with serum concentrations of the counterregulatory IL-1 receptor antagonist. Based on the evidence for IL-1β activation in PFAPA flares, we treated five PFAPA patients with a recombinant IL-1 receptor antagonist. All patients showed a prompt clinical and IP-10/CXCL10 response. Our data suggest an environmentally triggered activation of complement and IL-1β/-18 during PFAPA flares, with induction of Th1-chemokines and subsequent retention of activated T cells in peripheral tissues. IL-1 inhibition may thus be beneficial for treatment of PFAPA attacks, with IP-10/CXCL10 serving as a potential biomarker.

American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network 2015 Recommendations for the Treatment of Ankylosing Spondylitis and Nonradiographic Axial Spondyloarthritis

To provide evidence‐based recommendations for the treatment of patients with ankylosing spondylitis (AS) and nonradiographic axial spondyloarthritis (SpA).

Endoplasmic reticulum stress and the unfolded protein response are linked to synergistic IFN-β induction via X-box binding protein 1

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‐β 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‐β induction also occurs in HLA‐B27/human β2m‐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‐β induction by XBP‐1, which has implications for the immune response and the pathogenesis of diseases involving the UPR.

Subtype-specific peripheral blood gene expression profiles in recent onset juvenile idiopathic arthritis

OBJECTIVE To identify differences in peripheral blood gene expression between patients with different subclasses of juvenile idiopathic arthritis (JIA) and healthy controls in a multicenter study of patients with recent-onset JIA prior to treatment with disease-modifying antirheumatic drugs (DMARDs) or biologic agents. METHODS Peripheral blood mononuclear cells (PBMCs) from 59 healthy children and 136 patients with JIA (28 with enthesitis-related arthritis [ERA], 42 with persistent oligoarthritis, 45 with rheumatoid factor [RF]-negative polyarthritis, and 21 with systemic disease) were isolated from whole blood. Poly(A) RNA was labeled using a commercial RNA amplification and labeling system (NuGEN Ovation), and gene expression profiles were obtained using commercial expression microarrays (Affymetrix HG-U133 Plus 2.0). RESULTS A total of 9,501 differentially expressed probe sets were identified among the JIA subtypes and controls (by analysis of variance; false discovery rate 5%). Specifically, 193, 1,036, 873, and 7,595 probe sets were different in PBMCs from the controls compared with those from the ERA, persistent oligoarthritis, RF-negative polyarthritis, and systemic JIA patients, respectively. In patients with persistent oligoarthritis, RF-negative polyarthritis, and systemic JIA subtypes, up-regulation of genes associated with interleukin-10 (IL-10) signaling was prominent. A hemoglobin cluster was identified that was underexpressed in ERA patients but overexpressed in systemic JIA patients. The influence of JAK/STAT, ERK/MAPK, IL-2, and B cell receptor signaling pathways was evident in patients with persistent oligoarthritis. In systemic JIA, up-regulation of innate immune pathways, including IL-6, Toll-like receptor/IL-1 receptor, and peroxisome proliferator-activated receptor signaling, were noted, along with down-regulation of gene networks related to natural killer cells and T cells. Complement and coagulation pathways were up-regulated in systemic JIA, with a subset of these genes being differentially expressed in other subtypes as well. CONCLUSION Expression analysis identified differentially expressed genes in PBMCs obtained early in the disease from patients with different subtypes of JIA and in healthy controls, providing evidence of immunobiologic differences between these forms of childhood arthritis.

From HLA-B27 to spondyloarthritis: a journey through the ER.

Summary:  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.

HLA-B27 misfolding: a solution to the spondyloarthropathy conundrum?

Compelling evidence indicates that HLA-B27 is directly involved in the etiopathogenesis of the spondyloarthropathies (SpAs). Several hypotheses based on its native antigenic structure, the peptides it presents and mimicry with bacterial epitopes, have been proposed. However, these potential mechanisms remain largely unsupported by human studies and transgenic animal models. Recent work demonstrating that HLA-B27 misfolds offers a novel alternative hypothesis. Here, we review this new information on the folding and assembly of HLA-B27, and discuss consequences of misfolding that could be relevant to the pathogenesis of SpAs.

Lighting the fires within: the cell biology of autoinflammatory diseases

Autoinflammatory diseases are characterized by seemingly unprovoked pathological activation of the innate immune system in the absence of autoantibodies or autoreactive T cells. Discovery of the causative mutations underlying several monogenic autoinflammatory diseases has identified key regulators of innate immune responses. Recent studies have highlighted the role of misfolding, oligomerization and abnormal trafficking of pathogenic mutant proteins in triggering autoinflammation, and suggest that more common rheumatic diseases may have an autoinflammatory component. This coincides with recent discoveries of new links between endoplasmic reticulum stress and inflammatory signalling pathways, which support the emerging view that autoinflammatory diseases may be due to pathological dysregulation of stress-sensing pathways that normally function in host defence.