Innate immune signals in autoimmune and autoinflammatory uveitis

Gut microbiota and eye diseases: a bibliometric study and visualization analysis

Introduction

Recently the role of gut microbial dysbiosis in many ocular disorders, including but not limited to uveitis, age-related macular degeneration (AMD), diabetic retinopathy (DR), dry eye, keratitis and orbitopathy is a hot research topic in the field. Targeting gut microbiota to treat these diseases has become an unstoppable trend. Bibliometric study and visualization analysis have become essential methods for literature analysis in the medical research field. We aim to depict this area's research hotspots and future directions by bibliometric software and methods.

Methods

We search all the related publications from the Web of Science Core Collection. Then, CiteSpace was applied to analyze and visualize the country distributions, dual-map overlay of journals, keyword bursts, and co-cited references. VOSviewer was employed to identify authors, co-cited authors, journals and co-cited journals and display the keyword co-occurrence networks.

Results

A total of 284 relevant publications were identified from 2009 to 2023. The number of studies has been small in the first five years and has grown steadily since 2016. These studies were completed by 1,376 authors from 41 countries worldwide, with the United States in the lead. Lin P has published the most papers while Horai R is the most co-cited author. The top journal and co-cited journal are both Investigative Ophthalmology & Visual Science. In the keyword co-occurrence network, except gut microbiota, inflammation becomes the keyword with the highest frequency. Co-citation analyses reveal that gut dysbiosis is involved in common immune- and inflammation-mediated eye diseases, including uveitis, diabetic retinopathy, age-related macular degeneration, dry eye, and Graves' orbitopathy, and the study of microbiomes is no longer limited to the bacterial populations. Therapeutic strategies that target the gut microbiota, such as probiotics, healthy diet patterns, and fecal microbial transplantation, are effective and critical to future research.

Conclusions

In conclusion, the bibliometric analysis displays the research hotspots and developmental directions of the involvement of gut microbiota in the pathogenesis and treatment of some ocular diseases. It provides an overview of this field's dynamic evolution and structural relationships.

The Conundrum of Psoriatic Arthritis: a Pathogenetic and Clinical Pattern at the Midpoint of Autoinflammation and Autoimmunity

Psoriatic arthritis (PsA) is a chronic inflammatory condition characterized by psoriasis, synovitis, enthesitis, spondylitis, and the possible association with other extra-articular manifestations and comorbidities. It is a multifaceted and systemic disorder sustained by complex pathogenesis, combining aspects of autoinflammation and autoimmunity. Features of PsA autoinflammation include the role of biomechanical stress in the onset and/or exacerbation of the disease; the evidence of involvement of the innate immune response mediators in the skin, peripheral blood and synovial tissue; an equal gender distribution; the clinical course which may encounter periods of prolonged remission and overlapping features with autoinflammatory syndromes. Conversely, the role of autoimmunity is evoked by the association with class I major histocompatibility complex alleles, the polyarticular pattern of the disease which sometimes resembles rheumatoid arthritis and the presence of serum autoantibodies. Genetics also provide important insights into the pathogenesis of PsA, particularly related to class I HLA being associated with psoriasis and PsA. In this review, we provide a comprehensive review of the pathogenesis, genetics and clinical features of PsA that endorse the mixed nature of a disorder at the crossroads of autoinflammation and autoimmunity.

Targeting TBK1 attenuates ocular inflammation in uveitis by antagonizing NF-κB signaling

Uveitis with complex pathogenesis is a kind of eye emergency involving refractory and blinding inflammation. Dysregulation of TANK binding kinase 1 (TBK1), which plays an important role in innate immunity, often leads to inflammatory diseases in various organs. However, the role of TBK1 in uveitis remains elusive. In this study, we identified that the mRNA expression level of TBK1 and its phosphorylation level were significantly increased in peripheral blood mononuclear cells (PBMCs) of patients with uveitis. Consistent with this, the expression of Tbk1 was elevated in the ocular tissues of uveitis rats and primary peritoneal macrophages while its phosphorylation levels, which present activation forms, were upregulated as well, accompanied by an increase in the level of nuclear factor-κB (NF-κB) and proinflammatory cytokines. In addition, inhibition of TBK1 may effectively reduce the inflammatory response of uveitis rats by blocking NF-κB entry into the nucleus and impeding the initiation of NLRP3 inflammasome- and caspase-1-mediated pyroptosis pathways.

Molecular Surgery: Proteomics of a Rare Genetic Disease Gives Insight into Common Causes of Blindness

Rare diseases are an emerging global health priority. Although individually rare, the prevalence of rare "orphan" diseases is high, affecting approximately 300 million people worldwide. Treatments for these conditions are often inadequate, leaving the disease to progress unabated. Here, we review the clinical features and pathophysiology of neovascular inflammatory vitreoretinopathy (NIV), a rare inflammatory retinal disease caused by mutations in the CAPN5 gene. Although the prevalence of NIV is low (1 in 1,000,000 people), the disease mimics more common causes of blindness (e.g. uveitis, retinitis pigmentosa, proliferative diabetic retinopathy, and proliferative vitreoretinopathy) at distinct clinical stages. There is no cure for NIV to date. We highlight how personalized proteomics helped identify potential stage-specific biomarkers and drug targets in liquid vitreous biopsies. The NIV vitreous proteome revealed enrichment of molecular pathways associated with common retinal pathologies and implicated superior targets for therapeutic drug repositioning. In addition, we review our pipeline for collecting, storing, and analyzing ophthalmic surgical samples. This approach can be adapted to treat a variety of rare genetic diseases.

Expression of Cytokines in Porcine Iris, Retina and Choroidal Tissues Stimulated by Microbe-associated Molecular Patterns

PURPOSE

The innate immune system is strongly implicated in the pathogenesis of uveitis. This study was designed to clarify the responses of the innate immune system in uveal tissues.

MATERIALS AND METHODS

We utilized quantitative, real-time RT-PCR to measure mRNA of innate immune system receptors from porcine iris, choroid, and retina tissues. We used RT-PCR for cytokines to evaluate the responses of these tissues to specific ligands or extracts of whole bacteria that activate the innate immune system. We used ELISA for IL-6 on selected choroidal supernatants to confirm that the mRNA measurement correlated with protein levels.

RESULTS

In each of the studied tissues, we detected the expression of important receptors belonging to the innate immune system including dectin-1, TLR4, TLR8, and NOD2. Relative mRNA expression was generally lower in the retina compared to iris or choroid. All three tissues demonstrated upregulation of cytokine mRNA in response to a range of ligands that activate the innate immune system. The measurement of IL-6 protein was consistent with results based on mRNA. Notably, the expression of mRNA for IL-23 was more pronounced than IL-12 in all three tissues after stimulation with various innate immune system ligands.

CONCLUSIONS

These data provide evidence of a potent innate immune response intrinsic to uveal tissues. Specific innate immune system ligands as well as bacterial extracts enhanced the production of several inflammatory cytokines. Furthermore, the observation of higher upregulation of IL-23 mRNA, compared to IL-12 in response to innate immune stimuli, suggested that a local TH17 response might be more robust than a local TH1 response in uveal tissues. Our results expand the understanding as to how the innate immune system may contribute to uveitis.

DAPT reverses the Th17/Treg imbalance in experimental autoimmune uveitis in vitro via inhibiting Notch signaling pathway

Uveitis is the most common cause in inflammatory eye diseases that can lead to visual impairment even blindness worldwide. T helper (Th) 17 and regulatory T (Treg) cells are critical mediators for immune response. Notch signaling can regulate the cell differentiation, playing a role in the pathogenesis of the diseases. In this study, we measured the expression levels of Notch1, DLL4, IL-10, IL-17, RORγt and Foxp3 in T cells from lymph node, spleen and eye tissues in experimental autoimmune uveitis (EAU) rats in vitro, determined the ratios of CD4⁺/CD8⁺ and Th17/Treg. Moreover, we also investigated the effect of Notch signaling inhibitor N-(N-(3,5-Difluorophenacetyl-L-alanyl))-S-phenylglycine t-Butyl Ester (DAPT) on Notch1, DLL4 expression and on Th17, Treg cell differentiation. The results indicated that the pathogenesis of uveitis accompanied by the elevated expression of Notch1, DLL4, IL-10, IL-17, RORγt, and Foxp3 as well as the imbalanced CD4⁺/CD8⁺ and Th17/Treg ratios. By contrast, inhibition of Notch signaling by DAPT can efficiently decrease Th17 cell response, downregulate the expression of Notch1, DLL4, IL-17 and the transcription of RORγt, reduce Th17 levels and restore the CD4⁺/CD8⁺, Th17/Treg balance. Moreover, DAPT can also inhibit Th17 cell differentiation in healthy rats, though the inhibitory capacity of Th17, Treg differentiation is less than that in EAU rats. Overall, Notch signaling activation can lead to the disturbed Th17/Treg balance in uveitis, whereas inhibition of Notch signaling can ameliorate the inflammatory response and may be a potential immunoregulatory strategy in patients with uveitis.

Elevated Tear Human Neutrophil Peptides 1-3, Human Beta Defensin-2 Levels and Conjunctival Cathelicidin LL-37 Gene Expression in Ocular Rosacea

Purpose: To investigate the role of innate immunity in ocular rosacea. Methods: Thirty-two patients with ocular rosacea patients (group-1) and 28 healthy volunteers (group-2) who served as controls were enrolled in the study. Tear function parameters were assessed, conjunctival impression cytology was performed and tear samples were collected. Human-neutrophil-peptides (HNP) 1-3 and human-beta-defensin-2 (hBD-2) levels were measured in tears by using ELISA tests. Cathelicidin leucin-leucin-37 (LL-37), hBD-2, human-beta-defensin-9 (hBD-9) gene expression levels were measured in the conjunctival impression cytology samples using real-time polymerase chain reaction. Results: Tear HNP1-3 (p = 0.024), hBD-2 (p < 0.001), conjunctival LL-37 gene expression rate (p = 0.014) and ocular surface disease index scores (p = 0.001) were higher and the tear break-up time was lower (p = 0.003) in group-1. No other differences were found between the groups. Conclusion: The results of this study suggest the role of abnormal innate immunity in the pathophysiology of ocular rosacea by revealing elevated antimicrobial peptide levels.

Augmenting Endogenous Levels of Retinal Annexin A1 Suppresses Uveitis in Mice

PURPOSE

The purpose of this study was to examine the expression of the anti-inflammatory protein Annexin A1 (AnxA1) in mice and human retinae during uveitis and to determine whether local administration of human recombinant AnxA1 (hrAnxA1) can suppress uveitis in mice.

METHODS

Retinal sections from mice (healthy normal and uveitis) and postmortem human (no history of eye disease (n = 5) and uveitis (n = 7)) were stained for AnxA1 expression and imaged by immunofluorescence microscopy. AnxA1 cellular expression was determined by colabeling with CD45, glial fibrillary acidic protein (GFAP), and Iba-1 cells, with additional staining of AnxA1 receptors formyl peptide receptor 1 (FPR1) and FPRL1/FPR2. Mice with acute endotoxin-induced uveitis and chronic experimental autoimmune uveitis were treated locally by intravitreal injection with hrAnxA1, and disease was assessed by clinical scoring and quantification of leukocyte infiltrate via flow cytometry.

RESULTS

Constitutive expression of AnxA1 was observed in both healthy mouse and human retinae, and its expression increased during uveitis compared to healthy controls. AnxA1 colocalizes predominantly with CD45⁺ cells, GFAP⁺ macroglia, and to a lesser extent, Iba-1⁺ myeloid cells. We also demonstrate that local treatment with hrAnxA1 attenuates the severity of uveitis in mice.

CONCLUSIONS

These data indicate that locally expressed AnxA1 is elevated in the retina during intraocular inflammation. We demonstrate that local administration of hrAnxA1 to augment levels results in suppression of uveitis in mice.

TRANSLATIONAL RELEVANCE

Our data suggest that elevated expression of retinal AnxA1 in human uveitis may be immunoregulatory and that local supplementation with hrAnxA1 may provide a potential novel treatment for inflammatory eye diseases such as noninfectious uveitis.

Dopaminergic Regulation of Innate Immunity: a Review

Dopamine (DA) is a neurotransmitter in the central nervous system as well as in peripheral tissues. Emerging evidence however points to DA also as a key transmitter between the nervous system and the immune system as well as a mediator produced and released by immune cells themselves. Dopaminergic pathways have received so far extensive attention in the adaptive branch of the immune system, where they play a role in health and disease such as multiple sclerosis, rheumatoid arthritis, cancer, and Parkinson's disease. Comparatively little is known about DA and the innate immune response, although DA may affect innate immune system cells such as dendritic cells, macrophages, microglia, and neutrophils. The present review aims at providing a complete and exhaustive summary of currently available evidence about DA and innate immunity, and to become a reference for anyone potentially interested in the fields of immunology, neurosciences and pharmacology. A wide array of dopaminergic drugs is used in therapeutics for non-immune indications, such as Parkinson's disease, hyperprolactinemia, shock, hypertension, with a usually favorable therapeutic index, and they might be relatively easily repurposed for immune-mediated disease, thus leading to innovative treatments at low price, with benefit for patients as well as for the healthcare systems.

[Sarcoidosis and uveitis : An update]

Ocular involvement in sarcoidosis is present in up to one third of patients and is frequently manifested before the underlying systemic disease has been diagnosed. With a view to the therapeutic consequences an early diagnosis of the underlying disease is advantageous. In cases of visual loss early diagnostic measures include invasive procedures, such as ultrasound-guided bronchoalveolar lavage and transbronchial biopsy, if nodular conjunctival or cutaneous manifestations which would confirm the diagnosis are not present. Sufficiently sensitive biomarkers of disease activity have not yet been identified. As elevated activity of angiotensin-converting enzyme (ACE) and lysozyme are associated with disease activity they may be supportive of but not specific for the diagnosis. Other indicators include calcemia, calciuria, augmented activity of hepatic enzymes, cutaneous anergy and hilar changes in the lungs. In patients with newly diagnosed anterior uveitis presenting with granulomatous mutton-fat corneal precipitates, snow balls and vitreous body base condensates with mild retinal periphlebitis in intermediate uveitis as well as multifocal choroiditis (creamy choroidal lesions at different stages of activity and approximately 500 µm in diameter), a diagnosis of sarcoidosis has to be considered and tuberculosis should be excluded, even in the absence of a known systemic disease. Anterior uveitis is frequently a self-limiting condition, which can be well-controlled with topical steroids. On the other hand, intermediate, posterior and panuveitis are typically associated with a chronic course and require systemic therapy to prevent severe loss of vision. If the response to systemic corticosteroids is insufficient, treatment with immunomodulatory agents and biologics is initiated at progressively earlier stages, with a view to averting permanent organ damage and frequently with a positive impact on the short and long-term outcomes, even in therapy-refractive cases.

Phenotypic changes of peripheral blood mononuclear cells upon corticosteroid treatment in idiopathic intermediate uveitis

We analyzed phenotype and function of peripheral blood mononuclear cells in 9 patients with active idiopathic intermediate uveitis (IIU) before and after 6 and 12weeks of systemic corticosteroid (CS) treatment and compared to 28 healthy individuals. Monocytes from IIU patients showed increased MHCII expression compared with controls (p=0.09). Treatment reduced expression of MHCII, CD86, CD39 and CD124 (all p<0.05), whereas the percentage of CD121b-expressing monocytes was increased by week 6 (p=0.039). Patients showed alterations in T cell polarization (Th1/Th2 ratio: patients 5.2 versus controls 3.1, p=0.054; Th17/Treg ratio: 3.0 versus 1.7, p=0.027). S100A12 serum levels were higher in active IIU (p=0.057). Phagocytosis, oxidative burst and serum cytokine levels did not differ between patients and controls, and were not altered by treatment. In conclusion, monocytes from patients with active IIU show increased co-stimulatory capacities, which are modulated by systemic CS treatment, whereas innate immune cell functions are not altered.

Primed Mycobacterial Uveitis (PMU): Histologic and Cytokine Characterization of a Model of Uveitis in Rats

PURPOSE

The purpose of this study was to compare the histologic features and cytokine profiles of experimental autoimmune uveitis (EAU) and a primed mycobacterial uveitis (PMU) model in rats.

METHODS

In Lewis rats, EAU was induced by immunization with interphotoreceptor binding protein peptide, and PMU was induced by immunization with a killed mycobacterial extract followed by intravitreal injection of the same extract. Clinical course, histology, and the cytokine profiles of the aqueous and vitreous were compared using multiplex bead fluorescence immunoassays.

RESULTS

Primed mycobacterial uveitis generates inflammation 2 days after intravitreal injection and resolves spontaneously 14 days later. CD68+ lymphocytes are the predominant infiltrating cells and are found in the anterior chamber, surrounding the ciliary body and in the vitreous. In contrast to EAU, no choroidal infiltration or retinal destruction is noted. At the day of peak inflammation, C-X-C motif ligand 10 (CXCL10), IL-1β, IL-18, and leptin were induced in the aqueous of both models. Interleukin-6 was induced 2-fold in the aqueous of PMU but not EAU. Cytokines elevated in the aqueous of EAU exclusively include regulated on activation, normal T cell expressed and secreted (RANTES), lipopolysaccharide-induced CXC chemokine (LIX), growth-related oncogene/keratinocyte chemokine (GRO/KC), VEGF, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), and IL-17A. In the vitreous, CXCL10, GRO/KC, RANTES, and MIP-1α were elevated in both models. Interleukin-17A and IL-18 were elevated exclusively in EAU.

CONCLUSIONS

Primed mycobacterial uveitis generates an acute anterior and intermediate uveitis without retinal involvement. Primed mycobacterial uveitis has a distinct proinflammatory cytokine profile compared with EAU, suggesting PMU is a good complementary model for study of immune-mediated uveitis. CXCL10, a proinflammatory cytokine, was increased in the aqueous and vitreous of both models and may be a viable therapeutic target.

Two Genetic Variations in the IRF8 region are associated with Behçet's disease in Han Chinese

Several modulatory factors in the TLR signaling pathway including IRF3, IRF7, IRF8, TRIM20, MYD88 and NF-κB1 have been associated with autoimmune disease. In this study, we investigated the association of 13 SNPs for these genes with Behçet’s disease (BD) and Vogt-Koyanagi-Harada (VKH) syndrome using a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) assay. Haplotype and linkage disequilibrium (LD) analysis were performed by Haploview4.2. IRF8 mRNA expression and cytokine production was tested by real-time PCR and ELISA. Two SNPs near IRF8 were associated with BD (for rs17445836 GG genotype, Pc = 9.56 × 10⁻⁸, OR = 2.044; for rs11642873 AA genotype, Pc = 9.24 × 10⁻⁷, OR = 1.776). No significant association was found for the 13 SNPs tested with VKH syndrome. Haplotype analysis of the two positive SNPs revealed that the AG haplotype was significantly increased in BD patients (Pc = 2.60 × 10⁻⁸, OR = 1.646). Functional studies revealed an increased mRNA expression of IRF8 and IFN-γ production and a decreased production of IL-10 in rs17445836 carriers with the GG genotype. Increased expression of IRF8 as well as IFN-γ production and a decreased production of IL-10 were found in individuals carrying the rs11642873/AA genotype. In conclusion, this study indicates that IRF8 may contribute to the genetic susceptibility of BD by regulating IRF8 expression and cytokine production.

Gene delivery of a viral anti-inflammatory protein to combat ocular inflammation

Inflammation of the retina is a contributing factor in ocular diseases such as uveitis, diabetic retinopathy, and age-related macular degeneration (AMD). The M013 immunomodulatory protein from myxoma virus has been shown to interfere with the proinflammatory signaling pathways involving both the NLRP3 inflammasome and NF-κB. We have developed and characterized an adeno-associated viral (AAV) vector that delivers a secretable and cell-penetrating form of the M013 protein (TatM013). The expressed TatM013 protein was secreted and blocked the endotoxin-induced secretion of interleukin (IL)-1β in monocyte-derived cells and the reactive aldehyde-induced secretion of IL-1β in retinal pigment epithelium cells. The local anti-inflammatory effects of AAV-delivered TatM013 were evaluated in an endotoxin-induced uveitis (EIU) mouse model after intravitreal injection of mice with an AAV2-based vector carrying either TatM013 fused to a secreted green fluorescent protein (GFP) tag (sGFP-TatM013) or GFP. Expression of the sGFP-TatM013 transgene was demonstrated by fluorescence funduscopy in living mice. In EIU, the number of infiltrating cells and the concentration of IL-1β in the vitreous body were significantly lower in the eyes injected with AAV-sGFP-TatM013 compared with the eyes injected with control AAV-GFP. These results suggest that a virus-derived inhibitor of the innate immune response, when delivered via AAV, could be a generalized therapy for various inflammatory diseases of the eye.

Equine recurrent uveitis: Human and equine perspectives

Equine recurrent uveitis (ERU) is a spontaneous disease characterised by repeated episodes of intraocular inflammation. The epidemiology of ERU has not been fully elucidated, but the condition appears to be much more common in horses than is recurrent uveitis in humans, especially in certain breeds and geographical regions. Both humans and horses show a similarly altered immune response and a marked autoimmune response as the primary disease pathophysiology. However, an inciting cause is not always clear. Potential inciting factors in horses include microbial agents such as Leptospira spp. Microbial factors and genetic predisposition to the disease may provide clues as to why the horse appears so susceptible to this disease. The aim of this review is to discuss the immunology and genetics of ERU, compare the disease in horses with autoimmune anterior uveitis in humans, and discuss potential reasons for the increased prevalence in the horse.

CD14++CD16+ Monocytes Are Enriched by Glucocorticoid Treatment and Are Functionally Attenuated in Driving Effector T Cell Responses

Human peripheral monocytes have been categorized into three subsets based on differential expression levels of CD14 and CD16. However, the factors that influence the distribution of monocyte subsets and the roles that each subset plays in autoimmunity are not well studied. In this study, we show that circulating monocytes from patients with autoimmune uveitis exhibit a skewed phenotype toward intermediate CD14(++)CD16(+) cells, and that this is associated with glucocorticoid therapy. We further demonstrate that CD14(++)CD16(+) monocytes from patients and healthy control donors share a similar cell-surface marker and gene expression profile. Comparison of the effects of intermediate CD14(++)CD16(+) monocytes with classical CD14(++)CD16(-) and nonclassical CD14(+)CD16(++) monocytes revealed that the intermediate CD14(++)CD16(+) subset had an attenuated capacity to promote both naive CD4(+) T cell proliferation and polarization into a Th1 phenotype, and memory CD4(+) T cell proliferation and IL-17 expression. Furthermore, CD14(++)CD16(+) cells inhibit CD4(+) T cell proliferation induced by other monocyte subsets and enhance CD4(+) T regulatory cell IL-10 expression. These data demonstrate the impact of glucocorticoids on monocyte phenotype in the context of autoimmune disease and the differential effects of monocyte subsets on effector T cell responses.

Gene therapy with the caspase activation and recruitment domain reduces the ocular inflammatory response

Inflammation is a key component of chronic and acute diseases of the eye. Our goal is to test anti-inflammatory genes delivered by an adeno-associated virus (AAV) vector as potential treatments for retinal inflammation. We developed a secretable and cell penetrating form of the caspase activation and recruitment domain (CARD) from the apoptosis-associated speck-like protein containing a CARD (ASC) gene that binds caspase-1 and inhibits its activation by the inflammasome. The secretion and cell penetration characteristics of this construct were validated in vitro by measuring its effects on inflammasome signaling in a monocyte cell line and in an retinal pigmented epithelium (RPE) cell line. This vector was then packaged as AAV particles and tested in the endotoxin-induced uveitis mouse model. Gene expression was monitored one month after vector injection by fluorescence fundoscopy. Ocular inflammation was then induced by injecting lipopolysaccharide into the vitreous and was followed by enucleation 24 hours later. Eyes injected with the secretable and cell penetrating CARD AAV vector had both a significantly lower concentration of IL-1β as well as a 64% reduction in infiltrating cells detected in histological sections. These results suggest that anti-inflammatory genes such as the CARD could be used to treat recurring inflammatory diseases like uveitis or chronic subacute inflammations of the eye.

Unresolved issues in theories of autoimmune disease using myocarditis as a framework

Many theories of autoimmune disease have been proposed since the discovery that the immune system can attack the body. These theories include the hidden or cryptic antigen theory, modified antigen theory, T cell bypass, T cell-B cell mismatch, epitope spread or drift, the bystander effect, molecular mimicry, anti-idiotype theory, antigenic complementarity, and dual-affinity T cell receptors. We critically review these theories and relevant mathematical models as they apply to autoimmune myocarditis. All theories share the common assumption that autoimmune diseases are triggered by environmental factors such as infections or chemical exposure. Most, but not all, theories and mathematical models are unifactorial assuming single-agent causation of disease. Experimental and clinical evidence and mathematical models exist to support some aspects of most theories, but evidence/models that support one theory almost invariably supports other theories as well. More importantly, every theory (and every model) lacks the ability to account for some key autoimmune disease phenomena such as the fundamental roles of innate immunity, sex differences in disease susceptibility, the necessity for adjuvants in experimental animal models, and the often paradoxical effect of exposure timing and dose on disease induction. We argue that a more comprehensive and integrated theory of autoimmunity associated with new mathematical models is needed and suggest specific experimental and clinical tests for each major theory that might help to clarify how they relate to clinical disease and reveal how theories are related.

Polymorphism of HLA-B27: 105 subtypes currently known

HLA-B27 has a high degree of genetic polymorphism, with 105 known subtypes, named HLA-B*27:01 to HLA-B*27:106, encoded by 132 alleles. The most common subtypes associated with ankylosing spondylitis are HLA-B*27:05 (Caucasians), HLA-B*27:04 (Chinese), and HLA-B*27:02 (Mediterranean populations). For Chinese populations, HLA-B*27:04 is associated with a greater ankylosing spondylitis risk than HLA-B*27:05. Two subtypes, HLA-B27*06 and HLA-B27*09, seem to have no disease association. These differential disease associations of HLA-B27 subtypes, and the recent discovery that ERAP1 is associated with ankylosing spondylitis for patients with HLA-B27, have increased attempts to determine the function of HLA-B27 in disease pathogenesis by studying hemodynamic features of its protein structure, alterations of its peptidome, aberrant peptide handling, and associated molecular events. However, after 40 years we still do not fully know how HLA-B27 predisposes to ankylosing spondylitis and related spondyloarthritis.

Complexities in the relationship between infection and autoimmunity

The possible role of infections in driving autoimmune disease (AD) has long been debated. Many theories have emerged including release of hidden antigens, epitope spread, anti-idiotypes, molecular mimicry, the adjuvant effect, antigenic complementarity, or simply that AD could be a direct consequence of activation or subversion of the immune response by microbes. A number of issues are not adequately addressed by current theories, including why animal models of AD require adjuvants containing microbial peptides in addition to self tissue to induce disease, and why ADs occur more often in one sex than the other. Reviews published in the past 3 years have focused on the role of the innate immune response in driving AD and the possible role of persistent infections in altering immune responses. Overall, recent evidence suggests that microbes activating specific innate immune responses are critical, while antigenic cross-reactivity may perpetuate immune responses leading to chronic autoinflammatory disease.