Toll-like receptors and IFN-alpha: partners in autoimmunity

Should we be targeting type 1 interferons in antiphospholipid syndrome?

Systemic autoimmune diseases are characterized by increased production of type I interferon (IFN-1) and upregulation of IFN-1-inducible genes, suggesting an important role of the IFN-1 pathway in their pathogenesis. Recent studies have demonstrated increased IFN-1 expression in both primary and secondary antiphospholipid syndrome (APS), along with increased toll-like receptor type 9 activity and plasmacytoid dendritic cell function. The increasing knowledge of the association between IFN-1 and APS pathology may provide a rationale for conducting clinical trials to assess the efficacy of IFN-1-targeting drugs in reducing APS-related complications. In this narrative review, we summarize the current knowledge on the role of IFN-1 in APS pathogenesis, explore its clinical implications, and examine the existing evidence regarding therapeutic options that have been investigated to date.

Corneal pain and experimental model development

The cornea is a valuable tissue for studying peripheral sensory nerve structure and regeneration due to its avascularity, transparency, and dense innervation. Somatosensory innervation of the cornea serves to identify changes in environmental stimuli at the ocular surface, thereby promoting barrier function to protect the eye against injury or infection. Due to regulatory demands to screen ocular safety of potential chemical exposure, a need remains to develop functional human tissue models to predict ocular damage and pain using in vitro-based systems to increase throughput and minimize animal use. In this review, we summarize the anatomical and functional roles of corneal innervation in propagation of sensory input, corneal neuropathies associated with pain, and the status of current in vivo and in vitro models. Emphasis is placed on tissue engineering approaches to study the human corneal pain response in vitro with integration of proper cell types, controlled microenvironment, and high-throughput readouts to predict pain induction. Further developments in this field will aid in defining molecular signatures to distinguish acute and chronic pain triggers based on the immune response and epithelial, stromal, and neuronal interactions that occur at the ocular surface that lead to functional outcomes in the brain depending on severity and persistence of the stimulus.

Increased Abundance of Plasmacytoid Dendritic Cells and Interferon-Alpha Induces Plasma Cell Differentiation in Patients of IgA Nephropathy

The roles of pDC and IFN-α have not been well defined in IgA nephropathy (IgAN). In this study, we investigated the abundance of pDCs and IFN-α in IgAN patients and the response of peripheral blood mononuclear cells (PBMCs) after stimulation of the pDC-preferred TLR9 ligand CpG2216. The effects of IFN-α on plasma cell differentiation and leukocyte migration were also investigated. Here, we found that the percentages of pDCs were increased in PBMCs of IgAN patients, than in those of healthy controls. Plasma levels of IFN-α proteins and abundance of plasma cells were higher in IgAN patients than in healthy donors. Plasma IFN-α levels were positively associated with proteinuria, renal IgM deposition, and renal tubular atrophy/interstitial fibrosis grade in IgAN patients. Ex vivo activation of TLR9 on pDCs resulted in increased IFN-α production and enhanced plasma cell differentiation in IgAN patients as compared with healthy donors. IFN-α treatment led to increased plasma cell differentiation in vitro. IFN-α also significantly promoted expression of chemokines IP-10 and MCP-1 in human mesangial cells, which subsequently facilitated the transendothelial migration of human CD4⁺ and CD14⁺ cells. In conclusion, pDC and its secreted cytokine IFN-α may play important roles in pathological changes of IgA nephropathy.

Genomic profiling of host responses to Lassa virus: therapeutic potential from primate to man

Lassa virus infection elicits distinctive changes in host gene expression and metabolism. We focus on changes in host gene expression that may be biomarkers that discriminate individual pathogens or may help to provide a prognosis for disease. In addition to assessing mRNA changes, functional studies are also needed to discriminate causes of disease from mechanisms of host resistance. Host responses that drive pathogenesis are likely to be targets for prevention or therapy. Host responses to Lassa or its related arenaviruses have been monitored in cell culture, in animal models of hemorrhagic fever, in Lassa-infected nonhuman primates and, to a limited extent, in infected human beings. Here, we describe results from those studies and discuss potential targets for reducing virus replication and mitigating disease.

Prevention or acceleration of type 1 diabetes by viruses

Type 1 diabetes is an autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells. Even though extensive scientific research has yielded important insights into the immune mechanisms involved in pancreatic β-cell destruction, little is known about the events that trigger the autoimmune process. Recent epidemiological and experimental data suggest that environmental factors are involved in this process. In this review, we discuss the role of viruses as an environmental factor on the development of type 1 diabetes, and the immune mechanisms by which they can trigger or protect against this pathology.

Characteristics of plasmacytoid dendritic cell and CD4+ T cell in HIV elite controllers

Despite variability, the majority of HIV-1-infected individuals progress to AIDS characterized by high viral load and massive CD4+ T-cell depletion. However, there is a subset of HIV-1-positive individuals that does not progress and spontaneously maintains an undetectable viral load. This infrequent patient population is defined as HIV-1 controllers (HIV controllers), and represents less than 1% of HIV-1-infected patients. HIV-1-specific CD4+ T cells and the pool of central memory CD4+ T cells are also preserved despite immune activation due to HIV-1 infection. The majority of HIV controllers are also defined by the absence of massive CD4+ T-cell depletion, even after 10 years of infection. However, the mechanisms involved in protection against HIV-1 disease progression have not been elucidated yet. Controllers represent a heterogeneous population; we describe in this paper some common characteristics concerning innate immune response and CD4+ T cells of HIV controllers.

Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observations.

Activated expression of the chemokine Mig after chemotherapy contributes to chemotherapy-induced bone marrow suppression and lethal toxicity

Alterations in gene expression after chemotherapy may potentially help to identify mediators that induce suppression or regeneration in bone marrow. This paper reports our observation that the expression of the chemokine monokine induced by IFN-γ (Mig) and its receptor CXCR3 was significantly activated in mice after treatment with the chemotherapeutic agent 5-fluorouracil (5-FU). The neutralization of antibodies against the activated Mig increased the survival rate and accelerated BM recovery after chemotherapy. In addition, elevation of Mig plasma levels after 5-FU treatment corresponded with increased mortality. The cell cycle-inhibiting effect of the prophylactic administration of Mig protected hematopoietic progenitor cells (HPCs) from 1-β-d-arabinofuranosylcytosine in spleen colony assays and enhanced the irradiated recipients' survival. In CXCR3(-/-) mice, Mig did not propagate BM suppression, indicating that the suppressive effect of Mig is dependent on CXCR3. On the one hand, Mig stimulated p70 S6K and Erk1/2 pathways in mesenchymal stroma cells, inhibiting mesenchymal stroma cell-dependent HPC expansion. Moreover, Mig suppressed the STAT5 pathway in HPCs, inhibiting leukocyte differentiation. Our results strongly suggest that Mig contributes to the acute lethal toxicity arising from 5-FU administration. Neutralization of Mig may offer new strategies to alleviate BM toxicity with potentially dramatic implications for chemotherapy.

Role of AS04 in human papillomavirus vaccine: mode of action and clinical profile

INTRODUCTION

Understanding the mode of action of adjuvants is important for the interpretation of clinical studies.

AREAS COVERED

This paper discusses how the results of GSK's clinical studies with an AS04-adjuvanted human papillomavirus (HPV) vaccine are supported by the mode of action of AS04. AS04 and antigens must be injected at the same intramuscular site together or within 24 h of each other. AS04 induces local cytokine production leading to increased recruitment of dendritic cells and monocytes and raised numbers of antigen presenting cells in the draining lymph node. The localized and transient nature of the innate immune response supports the acceptable safety profile observed in clinical studies. The readers will gain a comprehensive understanding of the mode of action of AS04 and how it relates to results of clinical studies.

EXPERT OPINION

The AS04-adjuvanted HPV vaccine has an acceptable safety profile and induces an enhanced and sustained immune response and high protection against HPV types 16/18. Cross-protection against oncogenic HPV types 31/33/45 not contained in the vaccine is also observed. The mode of action of AS04 supports the clinical profile of the AS04-adjuvanted HPV vaccine.

Plasmacytoid dendritic cells in HIV infection: striking a delicate balance

pDC are the most potent IFN-alpha-producing cells in the body and serve as a vital link between innate and adaptive immunity. Deficiencies in pDC function were among the earliest observations of immune dysfunction in HIV-1 infection. Herein, we review the status of pDC in individuals with HIV-1 infection and the potential role of these cells in pathogenesis. We begin by reviewing the basic properties of pDC and then discuss the compromise in circulating pDC numbers and function in early and viremic HIV-1 infection and mechanisms that might account for their depletion in HIV-infected patients. In addition, we review the evidence that chronic production of IFN-alpha, probably through the chronic activation of pDC, is central to the immune activation that is so detrimental in HIV infection. Finally, we discuss the importance of balance in pDC numbers and function and the potential value of using absolute pDC counts and function as a biomarker, along with CD4(+) cell counts and VL in HIV-1-infected patients.

Celiac disease

PURPOSE OF REVIEW

Research in celiac disease is unraveling new findings at a high rate, and major advances seem to occur in all areas such as genetics, environmental factor, pathophysiology, and even prospective therapeutic implications.

RECENT FINDINGS

New insight is being gained into the interplay between genetic and environmental factors causing celiac disease. In addition to the known human leukocyte antigen haplotypes, genome-wide studies have now identified additional susceptibility loci and the majority of newly discovered risk regions harbor genes controlling immune pathways. The mechanism of translocation of gliadin peptides across the intestinal barrier has been the subject of much investigation, and there is now evidence that the toxic 33-mer peptide can also be translocated transcellularly. As for the paracellular route, this appears to be enhanced by gliadin's stimulation of zonulin release. The growing role of the innate immunity is being recognized and the increased expression of some Toll-like receptors appears to delineate a new inherent defect in this branch of innate immunity. Finally, new perspectives are opening in the treatment of celiac disease based on new detoxified grains, enzymatic degradation of gluten, and prevention of its crossing the mucosal barrier.

SUMMARY

The pace of new knowledge in this 'ancient' disease is very fast, and this review outlines the principal lines of such exciting developments.

Chronic alcohol consumption generates a vulnerable immune environment during early SIV infection in rhesus macaques

BACKGROUND

Alcohol consumption is a common problem in HIV-infected individuals, and the effects of alcohol may alter the efficiency of the immune response, potentially aggravating the disease as well as affecting end organs, such as the brain. However, the elements of the virus-host interaction that are modulated by ethanol are poorly dissected.

METHODS

Ethanol intake was conditioned in rhesus macaques prior to SIV infection, in order to mimic this common human behavior, and allow the evaluation of aspects of the virus-immune system interactions during acute time-points, when important facets of the infection are set up and when virus reproducibly enters the brain.

RESULTS

Although ethanol had a limited effect on the acute plasma viral load, it resulted in reduced circulating memory CD4(+) T cells and increased levels of monocytes expressing the viral coreceptor CCR5. In organs, ethanol consumption impacted immune cells in the liver as well as lymphoid and other nonlymphoid tissues, where CD4(+) T cells were predominantly affected.

CONCLUSION

Overall, the consumption of alcohol causes immune cell alterations that can contribute to the generation of a disease susceptible environment upon SIV infection.

Dendritic cells and cytokines in human inflammatory and autoimmune diseases

Dendritic cells (DCs) produce cytokines and are susceptible to cytokine-mediated activation. Thus, interaction of resting immature DCs with TLR ligands, for example nucleic acids, or with microbes leads to a cascade of pro-inflammatory cytokines and skewing of T cell responses. Conversely, several cytokines are able to trigger DC activation (maturation) via autocrine, for example TNF and plasmacytoid DCs, and paracrine, for example type I IFN and myeloid DCs, pathways. By controlling DC activation, cytokines regulate immune homeostasis and the balance between tolerance and immunity. The increased production and/or bioavailability of cytokines and associated alterations in DC homeostasis have been implicated in various human inflammatory and autoimmune diseases. Targeting these cytokines with biological agents as already is the case with TNF and IL-1 represents a success of immunology and the coming years will expand the range of cytokines as therapeutic targets in autoinflammatory and autoimmune pathology.

Toll-like receptors and innate immune responses in systemic lupus erythematosus

A series of discoveries over the past several years has provided a new paradigm for understanding autoimmunity in systemic lupus erythematosus. The discoveries of pattern recognition receptors and of how these receptors can be recruited into autoimmune responses underpin this paradigm. The implications of these observations continue to unfold with ongoing investigation into the range and specificity of pattern recognition receptors, into how immune complexes containing nucleic acids trigger these receptors, into how endogenous macromolecular 'danger signals' stimulate innate immune responses, and into the effect of pattern recognition receptor activation on various cell types in initiating and perpetuating autoimmunity. The development of clinical trials using therapeutic agents that target components of the innate immune system suggests that these advances may soon culminate in new medications for treating patients with systemic lupus erythematosus.

Sensing of viral infection and activation of innate immunity by toll-like receptor 3

Toll-like receptors (TLRs) form a major group of transmembrane receptors that are involved in the detection of invading pathogens. Double-stranded RNA is a marker for viral infection that is recognized by TLR3. TLR3 triggering activates specific signaling pathways that culminate in the activation of NF-kappaB and IRF3 transcription factors, as well as apoptosis, enabling the host to mount an effective innate immune response through the induction of cytokines, chemokines, and other proinflammatory mediators. In this review, we describe the paradoxical role of TLR3 in innate immunity against different viruses and in viral pathogenesis but also the evidence for TLR3 as a "danger" receptor in nonviral diseases. We also discuss the structure and cellular localization of TLR3, as well as the complex signaling and regulatory events that contribute to TLR3-mediated immune responses.

PI3K is critical for the nuclear translocation of IRF-7 and type I IFN production by human plasmacytoid predendritic cells in response to TLR activation

Plasmacytoid predendritic cells (pDCs) are the main producers of type I interferon (IFN) in response to Toll-like receptor (TLR) stimulation. Phosphatidylinositol-3 kinase (PI3K) has been shown to be activated by TLR triggering in multiple cell types; however, its role in pDC function is not known. We show that PI3K is activated by TLR stimulation in primary human pDCs and demonstrate, using specific inhibitors, that PI3K is required for type I IFN production by pDCs, both at the transcriptional and protein levels. Importantly, PI3K was not involved in other proinflammatory responses of pDCs, including tumor necrosis factor α and interleukin 6 production and DC differentiation. pDCs preferentially expressed the PI3K δ subunit, which was specifically involved in the control of type I IFN production. Although uptake and endosomal trafficking of TLR ligands were not affected in the presence of PI3K inhibitors, there was a dramatic defect in the nuclear translocation of IFN regulatory factor (IRF) 7, whereas nuclear factor κB activation was preserved. Thus, PI3K selectively controls type I IFN production by regulating IRF-7 nuclear translocation in human pDCs and could serve as a novel target to inhibit pathogenic type I IFN in autoimmune diseases.

Plasmacytoid dendritic cells and type I IFN: 50 years of convergent history

It has been 50 years since the initial descriptions of what are now known as plasmacytoid dendritic cells (pDC) and type I IFN. pDC, which are infrequent cells found in the peripheral blood and lymphoid organs, are the most potent producers of type I and type III IFNs in the body. pDC produce IFN-alpha in response to both DNA and RNA enveloped viruses by virtue of their ribonucleic acids signaling in the endosome through TLR9 and TLR7, respectively. This stimulation, which also occurs with DNA or RNA-containing immune complexes and synthetic TLR7 and -9 agonists, is dependent upon the transcription factor IRF-7, which is expressed at high constitutive levels in pDC. In addition to releasing as much as 3-10pg of IFN-alpha/cell, pDC are also potent modulators of the immune response. In this review, we discuss the signaling pathways in pDC, their roles in linking innate and adaptive immunity, and their roles in infectious disease and autoimmunity.