Persisting viruses and chronic inflammation: understanding their relation to autoimmunity

TLR4-Mediated Recognition of Mouse Polyomavirus Promotes Cancer-Associated Fibroblast-Like Phenotype and Cell Invasiveness

The tumorigenic potential of mouse polyomavirus (MPyV) has been studied for decades in cell culture models and has been mainly attributed to nonstructural middle T antigen (MT), which acts as a scaffold signal adaptor, activates Src tyrosine kinases, and possesses transforming ability. We hypothesized that MPyV could also transform mouse cells independent of MT via a Toll-like receptor 4 (TLR4)-mediated inflammatory mechanism. To this end, we investigated the interaction of MPyV with TLR4 in mouse embryonic fibroblasts (MEFs) and 3T6 cells, resulting in secretion of interleukin 6 (IL-6), independent of active viral replication. TLR4 colocalized with MPyV capsid protein VP1 in MEFs. Neither TLR4 activation nor recombinant IL-6 inhibited MPyV replication in MEFs and 3T6 cells. MPyV induced STAT3 phosphorylation through both direct and MT-dependent and indirect and TLR4/IL-6-dependent mechanisms. We demonstrate that uninfected mouse fibroblasts exposed to the cytokine environment from MPyV-infected fibroblasts upregulated the expressions of MCP-1, CCL-5, and α-SMA. Moreover, the cytokine microenvironment increased the invasiveness of MEFs and CT26 carcinoma cells. Collectively, TLR4 recognition of MPyV induces a cytokine environment that promotes the cancer-associated fibroblast (CAF)-like phenotype in noninfected fibroblasts and increases cell invasiveness.

A Ciliary Motility Index for Activity Measurement in Cell Cultures With Respiratory Syncytial Virus

BACKGROUND

The respiratory epithelium is frequently infected by the respiratory syncytial virus, resulting in inflammation, a reduction in cilia activity and an increase in the production of mucus.

METHODS

In this study, an automatic method has been proposed to characterize the ciliary motility from cell cultures by means of a motility index using a dense optical flow algorithm. This method allows us to determine the ciliary beat frequency (CBF) together with a ciliary motility index of the cells in the cultures. The object of this analysis is to automatically distinguish between normal and infected cells in a culture.

RESULTS

The method was applied in 2 stages. It was concluded from the first stage that the CBF is not a good enough indicator to discriminate between the control and infected cultures. However, the ciliary motility index does succeed in discriminating between the control and infected cultures using the t test with a value t = 6.46 and P < .001. In the second stage, it has been shown that the ciliary motility index did not differ significantly between patients, and the analysis of variance test gives α = 0.05, F = 1.61, P = .20. A threshold for this index has been determined using a receiver operating characteristics analysis that gives an area under the curve of 0.93.

CONCLUSIONS

We have obtained a ciliary motility index that is able to discriminate between control and infected cultures after the eighth postinfection day. After infection, there is a rapid cilia loss of the cells and the measured CBF corresponds to the remaining noninfected cells. This is why the CBF does not discriminate between the control and the infected cells.

Anti-phospholipid syndrome: Current opinion on mechanisms involved, laboratory characterization and diagnostic aspects

Anti-phospholipid syndrome is a complex and severe clinical situation, associated with symptoms such as recurrent thrombosis, arterial or venous, at any site, pregnancy loss, and other related syndromes. These clinical burdens, are highly variable from patient to patient, and are associated with biological abnormalities, such as the presence of the Lupus Anticoagulant or phospholipid dependent antibodies, confirmed on two occasions at least 12 weeks apart. From the diagnosis standpoint, both, functional (clotting) or immunological assays, are difficult to standardize and to optimize, due to the absence of reference material, or a characteristic clinical group, and international reference preparations. Large cohort studies are necessary for defining the usefulness of each assay, in terms of specificity, sensitivity, accuracy and for following-up the disease evolution. Clotting assays are based on Activated Partial Thromboplastin Time (APTT) and diluted Russell Viper Venom Time (dRVVT), performed at low and high phospholipid concentration, or on 1:1 mixtures of tested sample and a normal plasma pool. They allow evaluation of the paradoxal effects of LAs, which are pro-thrombotic in vivo, and anticoagulant in vivo. Use of synthetic phospholipids improves assay specificities and sensitivities, especially in patients treated with anticoagulants. Immunoassays can also be used for testing phospholipid dependent antibodies, first identified and measured as anti-cardiolipin antibodies, but now characterized as targeted to phospholipid cofactor proteins: mainly β2GP1 (which exposes cryptic epitopes upon binding to phospholipids), and in some cases prothrombin, and more rarely Protein S, Factor XIII, Protein Z or Annexin V. Use of optimized assays designed with well-characterized anionic phospholipids, then complexed with highly purified phospholipid cofactor protein (mainly β2GP1), offers a better link between reactivity and clinical associations, than the former assays which were empirically designed with cardiolipin. Standardization also remains complicated due to the absence of international standards and harmonized quantitation units. Validation on large cohorts of negative and positive patients remains the key approach for defining assay performance and clinical usefulness. Laboratory practice for all these methods is now greatly facilitated thanks to the use of automated instruments and dedicated software. Along with clinical criteria, laboratory assays are of great usefulness for identification and confirmation of the anti-phospholipid syndrome and they allow disease follow-up when appropriate patient management is in place.

Ciliary motility activity measurement using a dense optical flow algorithm

Persistent respiratory syncytial virus (RSV) infections have been associated with the exacerbation of chronic inflammatory diseases, including chronic obstructive pulmonary disease (COPD). This virus infects the respiratory epithelium, leading to chronic inflammation, and induces the release of mucins and the loss of cilia activity, two factors that determine mucus clearance and the increase in sputum volume. In this study, an automatic method has been established to determine the ciliary motility activity from cell cultures by means of optical flow computation, and has been applied to 136 control cultures and to 144 RSV-infected cultures. The control group presented an average of cell surface with cilia motility per field of 41 ± 15 % (mean ± standard deviation), while the infected group presented a 11 ± 5 %, t-Student p<0.001. The cutoff value to classify a infected specimen was <17.89 % (sensitivity 0.94, specificity 0.93). This methodology has proved to be a robust technique to evaluate cilia motility in cell cultures.

Respiratory syncytial virus persistence in macrophages alters the profile of cellular gene expression

Viruses can persistently infect differentiated cells through regulation of expression of both their own genes and those of the host cell, thereby evading detection by the host’s immune system and achieving residence in a non-lytic state. Models in vitro with cell lines are useful tools in understanding the mechanisms associated with the establishment of viral persistence. In particular, a model to study respiratory syncytial virus (RSV) persistence in a murine macrophage-like cell line has been established. Compared to non-infected macrophages, macrophages persistently infected with RSV show altered expression both of genes coding for cytokines and trans-membrane proteins associated with antigen uptake and of genes related to cell survival. The biological changes associated with altered gene expression in macrophages as a consequence of persistent RSV infection are summarized.

Respiratory syncytial virus inhibits ciliagenesis in differentiated normal human bronchial epithelial cells: effectiveness of N-acetylcysteine

Persistent respiratory syncytial virus (RSV) infections have been associated with the exacerbation of chronic inflammatory diseases, including chronic obstructive pulmonary disease (COPD). This virus infects the respiratory epithelium, leading to chronic inflammation, and induces the release of mucins and the loss of cilia activity, two factors that determine mucus clearance and the increase in sputum volume. These alterations involve reactive oxygen species-dependent mechanisms. The antioxidant N-acetylcysteine (NAC) has proven useful in the management of COPD, reducing symptoms, exacerbations, and accelerated lung function decline. NAC inhibits RSV infection and mucin release in human A549 cells. The main objective of this study was to analyze the effects of NAC in modulating ciliary activity, ciliagenesis, and metaplasia in primary normal human bronchial epithelial cell (NHBEC) cultures infected with RSV. Our results indicated that RSV induced ultrastructural abnormalities in axonemal basal bodies and decreased the expression of β-tubulin as well as two genes involved in ciliagenesis, FOXJ1 and DNAI2. These alterations led to a decrease in ciliary activity. Furthermore, RSV induced metaplastic changes to the epithelium and increased the number of goblet cells and the expression of MUC5AC and GOB5. NAC restored the normal functions of the epithelium, inhibiting ICAM1 expression, subsequent RSV infection through mechanisms involving nuclear receptor factor 2, and the expression of heme oxygenase 1, which correlated with the restoration of the antioxidant capacity, the intracellular H(2)O(2) levels and glutathione content of NHBECs. The results presented in this study support the therapeutic use of NAC for the management of chronic respiratory diseases, including COPD.

The ambiguity in immunology

In the present article, we discuss the various ambiguous aspects of the immune system that render this complex biological network so highly flexible and able to defend the host from different external invaders. This ambiguity stems mainly from the property of the immune system to be both protective and harmful. Immunity cannot be fully protective without producing a certain degree of damage (immunopathology) to the host. The balance between protection and tissue damage is, therefore, critical for the establishment of immune homeostasis and protection. In this review, we will consider as ambiguous, various immunological tactics including: (a) the opposing functions driving immune responses, immune-regulation, and contra-regulation, as well as (b) the phenomenon of chronic immune activation as a result of a continuous cross-presentation of apoptotic T cells by dendritic cells. All these plans participate principally to maintain a state of chronic low-level inflammation during persisting infections, and ultimately to favor the species survival.

Molecular mimicry of human endothelial cell antigen by autoantibodies to nonstructural protein 1 of dengue virus

The pathogenesis of dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS), both serious complications of dengue virus (DV) infection, remains unclear. In this study, we found that anti-DV NS1 (nonstructural protein 1) polyclonal antibodies cross-reacted with human umbilical vein endothelial cells (HUVECs). We further identified a complex-specific mAb, DB16-1, which could recognize DV NS1 and cross-react with HUVECs and human blood vessels. The target protein of DB16-1 was further purified by immunoaffinity chromatography. LC-MS/MS analysis and co-immunoprecipitation revealed that the target protein of DB16-1 was human LYRIC (lysine-rich CEACAM1 co-isolated). Our newly generated anti-LYRIC mAbs bound to HUVECs in a pattern similar to that of DB16-1. The B-cell epitope of DB16-1 displayed a consensus motif, Lys-X-Trp-Gly (KXWG), which corresponded to amino acid residues 116-119 of DV NS1 and mimicked amino acid residues 334-337 in LYRIC. Moreover, the binding activity of DB16-1 in NS1 of DV-2 and in LYRIC disappeared after the KXWG epitope was deleted in each. In conclusion, DB16-1 targeted the same epitope in DV NS1 and LYRIC protein on human endothelial cells, suggesting that it might play a role in the pathogenesis of DHF/DSS. Future studies on the role of the anti-NS1 antibody in causing vascular permeability will undoubtedly be performed on sera collected from individuals before, during, and after the endothelial cell malfunction phase of a dengue illness.

Ocular manifestations of scleroderma

Systemic sclerosis is a chronic multi-system disorder predominantly affecting the skin, musculoskeletal, gastrointestinal, pulmonary, and renal systems. Although the exact etiology is unknown, recent evidence suggests that immune activation play a pivotal role in the pathogenesis. Ocular involvement in systemic sclerosis has been documented; however, due to the rare nature of the disease, most papers have been single case reports or small case series. This review paper aims to consolidate the findings of previous papers with a view to providing a comprehensive review of the ocular manifestations of systemic sclerosis.

Cultures of HEp-2 cells persistently infected by human respiratory syncytial virus differ in chemokine expression and resistance to apoptosis as compared to lytic infections of the same cell type

HEp-2 cells that survived a lytic infection with Human Respiratory Syncytial Virus (HRSV) were grown to obtain a persistently infected culture that produced relatively high amounts of virus (10(6)-10(7) pfu/ml) for more than twenty passages. The cells in this culture were heterogeneous with regard to the expression of viral antigens, ranging from high to undetectable levels. However, all cell clones derived from the persistent culture did not produce infectious virus or viral antigens and grew more slowly than the original uninfected HEp-2 cells. When these "cured" cell clones were infected with wild-type HRSV, delayed virus production and reduction in the number and size of syncytia were observed compared to lytically infected HEp-2 cells. Most significantly, differences in gene expression between persistently and lytically infected cultures were also observed, including genes that encode for cytokines, chemokines and other gene products that either promote cell survival or inhibit apoptosis. These results highlight the significantly different responses of the same cell type to HRSV infection depending on the outcome of such infection, i.e., lytic versus persistent.

TLR7 stimulation augments T effector-mediated rejection of skin expressing neo-self antigen in keratinocytes

Immunotherapy generally fails to induce tumour regression in spontaneously arising tumours. Failure is attributed to both tumour-related factors and an ineffective immune response. As a model of tumour immunotherapy, without the confounding effects of potential tumour-determined mechanisms of immune evasion, we studied the requirements for rejection of skin grafts expressing a neo-self antigen in somatic cells and not in antigen-presenting cells. When antigen expression was restricted to somatic cells, both CD4(+) and CD8(+) effector cells were required for graft rejection. Although freshly placed grafts were spontaneously rejected, healed grafts established under the cover of T cell depletion were not rejected even after T cell numbers recovered to a level where freshly placed grafts on the same animal were rejected, suggesting that healed skin grafts expressing a neo-self antigen only in somatic cells could not be rejected by primed recipients with functional effector T cells. Local TLR7 ligation induced inflammatory responses and rejection of healed grafts exposed to the TLR agonist but did not induce rejection of untreated healed grafts on the same animal. Thus, local pro-inflammatory signalling via TLR7 can promote effector T cell function against skin cells displaying their nominal antigen.

Detection of cytotoxic CD13-specific autoantibodies in sera from patients with ulcerative colitis and Crohn's disease

Recent evidence suggests an association between inflammatory bowel disease (IBD) and human cytomegalovirus (HCMV) infection, but the exact pathogenic role of HCMV in this disease remains unclear. HCMV infection has for a long time been known to be associated with various autoimmune manifestations and the formation of autoantibodies. Previous studies from our group have shown that HCMV is associated with a human protein, CD13 (aminopeptidase N) and that autoantibodies against this protein are frequently found in HCMV infected bone marrow transplant patients with chronic graft versus host disease. We have recently observed that 90% of IBD patients have an active HCMV infection. In this study, we examined the presence and cytotoxicity of CD13-specific autoantibodies in sera obtained from 28 patients with ulcerative colitis and 26 patients with Crohn's disease, and in sera obtained from healthy blood donors by using flow cytometric assays against mouse cells transfected with human CD13 or a microcytotoxicity assay against different CD13 positive human cells. Cytotoxic CD13-specific autoantibodies were identified in 66% of the sera obtained from HCMV-IgG positive patients with ulcerative colitis and in 58% of the sera obtained from HCMV-IgG positive patients with Crohn's disease, but not in control individuals. These cytotoxic autoantibodies may interfere with biological cell functions and could thereby contribute to the chronic inflammation in patients with IBD.

Evolution of the Intrahepatic T Cell Repertoire during Chronic Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection is characterized by extensive infiltration of inflammatory cells in the liver, where there is a compartmentalization of HCV-reactive T lymphocytes. Previous studies have demonstrated a broad intrahepatic TCR repertoire; however, there is little information regarding the stability of this intrahepatic T cell population. We studied the T cell repertoires in sequential liver biopsy samples from five individuals with chronic HCV infection using TCR spectratype analysis; four subjects had been treated with IFN-alpha during the interval between biopsies. Transcripts from most TCRBV families were detectable in the liver tissues, and 25-85% of these had skewed spectratype profiles indicative of T cell clonal expansions. Most of the intrahepatic T cell expansions were not evident in an analysis of peripheral blood T cells collected at the same time as the liver biopsy. Detailed analysis using TCRBJ-primed run-off reactions revealed that the intrahepatic TCR repertoires were not stable within an individual, although some TCR clonotypes were maintained for at least 45 months.

Acute disseminated encephalomyelitis in childhood: epidemiologic, clinical and laboratory features

BACKGROUND

Acute disseminated encephalomyelitis (ADEM) is a central nervous system demyelinating disease that usually follows an apparently benign infection in otherwise healthy young persons. The epidemiology, infectious antecedents and pathogenesis of ADEM are poorly characterized, and some ADEM patients are subsequently diagnosed with multiple sclerosis (MS).

METHODS

We retrospectively (1991-1998) and prospectively (1998-2000) studied all persons aged < 20 years diagnosed with ADEM from the 3 principal pediatric hospitals in San Diego County, CA, during 1991-2000. Acute neurologic abnormalities and imaging evidence of demyelination were required for study inclusion. Epidemiologic variables, risk factors, clinical course, laboratory and radiographic findings, neuropathology and treatment data were analyzed. Interleukin (IL)-12, interferon-gamma (IFN-gamma) and IL-10 were assayed in blinded manner on cerebrospinal fluid (CSF) obtained prospectively from a subset of ADEM cases and compared with CSF from patients with enteroviral (EV) meningoencephalitis confirmed by polymerase chain reaction (PCR) and controls without pleocytosis.

RESULTS

Data were analyzed on 42 children and adolescents diagnosed with ADEM during 1991-2000, and CSF IL-12, IFN-gamma and IL-10 levels were compared among ADEM (n = 14), EV meningoencephalitis (n = 14) and controls without pleocytosis (n = 28). Overall incidence of ADEM was 0.4/100,000/year; incidence quadrupled during 1998-2000 compared with earlier years. No gender, age stratum, ethnic group or geographic area was disproportionately affected. A total of 4 (9.5%) patients initially diagnosed with ADEM were subsequently diagnosed with MS after multiple episodes of demyelination. Although most children eventually recovered, 2 died, including 1 of the 3 ultimately diagnosed with MS. Magnetic resonance imaging was required for diagnosis among 74% of patients; computerized tomography findings were usually normal. Patients with EV had significantly higher mean CSF IFN-gamma (P = 0.005) and IL-10 (P = 0.05) than patients with ADEM and controls without CSF pleocytosis. CSF from ADEM patients had CSF cytokine values statistically similar to those of 3 patients subsequently diagnosed with MS.

CONCLUSIONS

ADEM is a potentially severe demyelinating disorder likely to be increasingly diagnosed as more magnetic resonance imaging studies are performed on patients with acute encephalopathy. Further characterization of the central nervous system inflammatory response will be needed to understand ADEM pathogenesis, to improve diagnostic and treatment strategies and to distinguish ADEM from MS.

Mechanisms inducing or controlling CD8+ T cell responses against self- or non-self-antigens

Cytotoxic T lymphocytes (CTLs) generally recognize antigens endogenously synthesized within the cells and presented in the form of peptides on class I molecules. However, a large body of evidence suggests that dendritic cells (DCs) have the capacity to capture and deliver exogenous antigens into the major histocompatibility complex (MHC) class I processing pathway. In this paper, we discuss this function, defined as cross-presentation, and how it is directed, particularly in inducing T cell tolerance, and how it requires special activating signals (such as CD40 ligand) to transform into a mechanism that provides either protective immunity or autoimmunity.

Langerhans cell histiocytosis: an evaluation of histopathological parameters, demonstration of proliferation by Ki-67 and mitotic bodies

PURPOSE

Langerhans cell histiocytosis (LCH) is a disease with a variable clinical manifestation, being localised (SS) or disseminated (MS). The etiology and pathogenesis of LCH is unknown. It is a proliferative disorder of monoclonal origin, but not necessarily neoplastic. In our study we evaluated histopathological parameters and proliferative activity in LCH.

MATERIALS AND METHODS

Infiltrates from 43 patients with LCH were investigated (nSS=32, nMS=11). We evaluated different histopathological parameters semiquantitatively, demonstrating proliferation using immunohistochemistry for Ki-67.

RESULTS

Overall, the histopathological picture of LCH was heterogeneous. The degree of eosinophilia and presence of necroses was significantly higher in SS-infiltrates compared to MS-infiltrates. Mitotic figures were detected in more than half the infiltrates. The Langerhans origin was verified by CD1a. Ki-67 was highly expressed in all but one infiltrate.

CONCLUSIONS

The presence of necrosis and the degree of eosinophilia are related to SS-disease in our study. Ki-67 expression and the presence of mitotic figures indicate that local proliferation contributes to the accumulation of Langerhans cells. Supported by the histopathological appearance of the lesions and a level of Ki-67 expression lower than that of neoplastic tissue, we suggest that LCH is a reactive condition, possibly induced by immunostimulation caused by unknown agents.

The appearance of S-100 protein-positive dendritic cells and the distribution of lymphocyte subsets in idiopathic nonspecific interstitial pneumonia

Idiopathic interstitial pneumonia (IIP) is a progressive interstitial lung disease of unknown etiology. We investigated dendritic cells in idiopathic nonspecific interstitial pneumonia (NSIP) immunohistochemically, using anti-S-100 protein antibody and anti-HLA-DR antibody and also evaluated the relationship between the distribution of S-100 protein-positive dendritic cells (S- 100 DCs) and the lymphocytic subsets in the lung tissue of NSIP. Fifteen patients with the pathological diagnosis of idiopathic NSIP and six patients with usual interstitial pneumonia (UIP) were recruited into this study. Many S-100 DCs were observed in all the cases of idiopathic NSIP but S-100 DCs were not recognized in UIP cases invariably. In the mirror section method, most S-100 DCs showed a positive reaction of anti-HLA-DR antibody but a negative reaction for anti-CD1a antibody. CD8 and CD4 positive lymphocytes were infiltrated diffusely around S-100 DCs. It was demonstrated that the infiltration of CD8 positive lymphocytes predominated in the fibrosing areas and lymphoid follicles around S-100 DCs more so than CD4 positive lymphocytes.We speculate that the pathogenesis of NSIP is different from UIP and that DC and T cell-mediated immune mechanisms may play a role in the development and perpetuation of NSIP.

A time to kill: viral manipulation of the cell death program

Many viruses have as part of their arsenal the ability to modulate the apoptotic pathways of the host. It is counter-intuitive that such simple organisms would be efficient at regulating this the most crucial pathway within the host, given the relative complexity of the host cells. Yet, viruses have the potential to initiate or stay the onset of programmed cell death through the manipulation of a variety of key apoptotic proteins. It is the intention of this review to provide an overview of viral gene products that are able to promote or inhibit apoptotic death of the host cell and to discuss their mechanisms of action. It is not until recently that the depth at which viruses exploit the apoptotic pathways of their host has been seen. This understanding may provide a great opportunity for future therapeutic ventures.

Epitope spreading in immune-mediated diseases: implications for immunotherapy

Evidence continues to accumulate supporting the hypothesis that tissue damage during an immune response can lead to the priming of self-reactive T and/or B lymphocytes, regardless of the specificity of the initial insult. This review will focus primarily on epitope spreading at the T-cell level. Understanding the cellular and molecular basis of epitope spreading in various chronic immune-mediated human diseases and their animal models is crucial to understanding the pathogenesis of these diseases and to the ultimate goal of designing antigen-specific treatments.

Autoantibody appearance in cytomegalovirus-infected liver transplant recipients: correlation with antigenemia

The presence of anti-endothelial cells (AECA), smooth muscle (SMA), antinuclear (ANA) and antimitochondrial (AMA) autoantibodies, and liver/kidney microsomal antibody type 1 (LKM1) was investigated retrospectively in sera of liver transplant patients and correlated with cytomegalovirus (CMV) infection as determined by the antigenemia test and with the appearance of acute or chronic allograft rejection. Indirect immunofluorescence analysis was carried out in sequential sera from 40 liver transplant patients. Ten out of 23 antigenemia-positive and none of the antigenemia-negative patients developed serum autoantibodies (P = 0.002, Fisher's exact test). Anti-endothelial cell autoantibodies were found in nine cases and SMA in four patients. Antinuclear antibodies were detected in one otherwise autoantibody-negative patient. All but one case of autoantibody positivity were observed in the high antigenemia group (P < 0.0001, Fisher's exact test). In all but one case, autoantibodies were detected in blood during the antigenemia phase and in most cases in coincidence with or after the antigenemia peak. Even though a statistically significant correlation was not found between autoantibody production and the development of acute or chronic allograft rejection, proportionally more acute rejection cases were observed in the autoantibody-positive than in the autoantibody-negative group. It has been speculated that CMV-induced endothelial damage may be a potent antigenic stimulus, which leads to the production of anti-endothelial cells autoantibodies. Anti-endothelial cell autoantibodies may represent not only a marker of cell injury but also contribute to the progression of the inflammatory response leading to the exposure of tissue-privileged self antigens and the induction of other autoantibodies such as SMA.

Control of the autoimmune response by type 2 nitric oxide synthase

Immune defense against pathogens often requires NO, synthesized by type 2 NO synthase (NOS2). To discern whether this axis could participate in an autoimmune response, we immunized NOS2-deficient mice with the autoantigen acetylcholine receptor, inducing muscle weakness characteristic of myasthenia gravis, a T cell-dependent Ab-mediated autoimmune disease. We found that the acetylcholine receptor-immunized NOS2-deficient mice developed an exacerbated form of myasthenia gravis, and demonstrated that NOS2 expression limits autoreactive T cell determinant spreading and diversification of the autoantibody repertoire, a process driven by macrophages. Thus, NOS2/NO is important for silencing autoreactive T cells and may restrict bystander autoimmune reactions following the innate immune response.

Innate immunity and autoimmunity: from self-protection to self-destruction

Innate immune responses provide the body with its first line of defense against infections. Signals generated by a subset of lymphocytes, including natural killer (NK) cells and natural killer T (NKT) cells, during the early host response might have an additional role in determining the nature of downstream adaptive immune responses. Here, Fu-Dong Shi, Hans-Gustaf Ljunggren and Nora Sarvetnick discuss the role of cellular and soluble components of innate immunity in the development of autoimmune diseases. Some putative pathways leading from innate immunity to autoimmunity are proposed.

Ongoing viral replication is required for gammaherpesvirus 68-induced vascular damage

The role of autoimmunity in large-vessel vasculitis in humans remains unclear. We have previously shown that infection of gamma interferon receptor knockout (IFN-gamma R(-/-)) mice with gammaherpesvirus 68 (gamma HV68) results in severe inflammation of the large elastic arteries that is pathologically similar to the lesions observed in Takayasu's arteritis, the nongranulomatous variant of temporal arteritis, and Kawasaki's disease (K. E. Weck et al., Nat. Med. 3:1346-1353, 1997). Here we define the mechanism of damage to the elastic arteries. We show that there is a persistent productive infection of the media of the large elastic vessels. In addition, we demonstrate that persistent virus replication is necessary for chronic arteritis, since antiviral therapy of mice with established disease resulted in increased survival, clearance of viral antigen from the media of the affected vessel, and dramatic amelioration of arteritic lesions. These data argue that ongoing virus replication, rather than autoimmunity, is the cause of gamma HV68-induced elastic arteritis.

Nasal application of a naturally processed and presented T cell epitope derived from TCR AV11 protects against adjuvant arthritis

Reactivity towards TCR peptides plays an important role in the regulation of several experimental autoimmune diseases. In a previous paper, we showed the TCRAV11 usage by an arthritogenic T cell clone isolated from a rat with adjuvant arthritis (AA). Moreover, we identified three immunogenic peptides in AV11: AV11 24-40, 41-55 and 66-80. In the present study, we show that T cells directed towards all three epitopes are part of the immune repertoire. The strongest delayed-type hypersensitivity (DTH) reaction was observed against the peptide derived from the third framework region, peptide AV11 66-80. DTH reactions to this peptide were detectable in naive rats and increased significantly after AA induction. Interestingly, modulation of the AV11 66-80 T cell response by nasal AV11 66-80 administration resulted in reduced DTH responses and in a strong inhibition of AA. These findings suggest that during the natural course of AA, T cells directed towards the third framework region of AV11 do not have a disease regulatory function, but instead play a role in the deterioration of AA.

Systemic sclerosis immunoglobulin G autoantibodies bind the human cytomegalovirus late protein UL94 and induce apoptosis in human endothelial cells

Systemic sclerosis is an autoimmune disease characterized by immunological and vascular abnormalities. Autoantibodies against intracellular antigens are associated with particular clinical features of the disease, whereas autoantibodies against cell surface antigens may be pathogenic by inducing endothelial cell damage, considered the primary event in the pathogenesis of the disease. Latent human cytomegalovirus infection may contribute to progression of systemic sclerosis through its ability to infect endothelial cells; however, direct links between human cytomegalovirus infection and systemic sclerosis are still lacking. Molecular mimicry is one of the mechanisms that account for the link between infection and autoimmunity. Here we have identified an immunodominant peptide using systemic sclerosis serum screening of a random peptide library; such peptide shares homology with autoantigens and with the human cytomegalovirus late protein UL94 (ref. 9). Immunoglobulin G antibodies against the peptide affinity-purified from the sera of patients with systemic sclerosis specifically recognized the viral product and autoantigens; moreover, such antibodies induced endothelial cell apoptosis through specific interaction with the cell surface integrin-NAG-2 protein complex. Our results provide evidence that antibodies against human cytomegalovirus cause apoptosis of endothelial cells, considered the initial pathogenic event of systemic sclerosis, and indicate a previously unknown mechanism for the etiological link between human cytomegalovirus infection and autoimmunity.

Persisting viruses and autoimmunity

Viral infections can be responsible for the onset and sustaining of autoimmune processes. We discuss how chronic inflammation associated with viral persistence is the prerequisite for initiation of a multi-step process leading to autoimmunity. Firstly, chronic inflammation may favor the priming of autoreactive T cells that have escaped thymic selection and are specific for self-mimicking viral peptides in the periphery. In addition, viral persistence and inflammation can act synergistically to induce and sustain autoimmunity either unveiling cryptic self-epitopes, or favoring determinant spreading, or activating dendritic cells, or promoting constant priming of new autoreactive T cells, or contributing to the efficient generation of effector cells, or, finally, restimulating memory T lymphocytes.

Short-lived immunization site inflammation in self-limited active experimental allergic encephalomyelitis

To understand the mechanisms underlying spontaneous remission of proteolipid protein (PLP) 139-151 peptide-induced experimental allergic encephalomyelitis (EAE), an acute autoimmune disease of SJL mice resembling human multiple sclerosis, we examined both the effector response site in the central nervous system (CNS) and the immunization site at different phases of the disease. In the CNS, the frequency of PLP 139-151 peptide-specific IFN-gamma-producing T cells as well as the amount of infiltrating CD4(+) and CD11b(+) cells decreased with recovery. However, IL-4-producing cells were always rare and cyclooxygenase-2(+) cells were numerous only at disease peak in the CNS, suggesting that T(h)2 cytokines and prostaglandins did not determine remission of EAE. By looking at the s.c. site of PLP 139-151 peptide plus adjuvant injection, we found that, although the inflammatory infiltrate was abundant, CD11b(+) cells started to decrease already during disease acute phase and DEC-205(+) cells were numerous only at early time points. We propose that immunization site inflammation is short-lived in PLP 139-151 peptide-induced EAE, and this leads to a temporary autoreactive T cell stimulation and to a self-limited disease.

Lack of Th2 cytokine increase during spontaneous remission of experimental allergic encephalomyelitis

The mechanisms underlying spontaneous remission of autoimmune diseases are presently unknown, though regulatory T cells are believed to play a major role in this process. We tested the hypothesis that Th2 and/or other T cell regulatory cytokines cause the spontaneous remission of experimental allergic encephalomyelitis (EAE), a model of Th1-mediated autoimmunity. We analyzed the cytokine profile of lymph node and central nervous system-infiltrating cells in individual SJL mice at different stages of proteolipid protein (PLP) 139-151 peptide-induced EAE. We found that IFN-gamma slowly fades away after clinical recovery, whereas IL-4, IL-10 and transforming growth factor-beta remain low or undetectable. Our peptide-results therefore suggest that regulatory T cells producing anti-inflammatory cytokines are not involved in spontaneous remission of EAE and challenge the view that the Th1/Th2 balance has a key role in EAE regulation.