Upregulation of OX40 ligand on monocytes contributes to early virological control in patients with chronic hepatitis C

IFN-γ Induces PD-L1 Expression in Primed Human Basophils

Programmed death-ligand 1 (PD-L1) plays a key role in maintaining immune tolerance and also in immune evasion of cancers and pathogens. Though the identity of stimuli that induce PD-L1 in various human innate cells and their function are relatively well studied, data on the basophils remain scarce. In this study, we have identified one of the factors, such as IFN-γ, that induces PD-L1 expression in human basophils. Interestingly, we found that basophil priming by IL-3 is indispensable for IFN-γ-induced PD-L1 expression in human basophils. However, priming by other cytokines including granulocyte-macrophage colony-stimulating factor (GM-CSF) and thymic stromal lymphopoietin (TSLP) was dispensable. Analyses of a published microarray data set on IL-3-treated basophils indicated that IL-3 enhances IFNGR2, one of the chains of the IFNGR heterodimer complex, and CD274, thus providing a mechanistic insight into the role of IL-3 priming in IFN-γ-induced PD-L1 expression in human basophils.

Liver, Tumor and Viral Hepatitis: Key Players in the Complex Balance Between Tolerance and Immune Activation

Liver cancer is the third most common cause of cancer related death in the World. From an epidemiological point of view the risk factors associated to primary liver cancer are mainly viral hepatitis infection and alcohol consumption. Even though there is a clear correlation between liver inflammation, cirrhosis and cancer, other emerging liver diseases (like fatty liver) could also lead to liver cancer. Moreover, the liver is the major site of metastasis from colon, breast, ovarian and other cancers. In this review we will address the peculiar status of the liver as organ that has to balance between tolerance and immune activation. We will focus on macrophages and other key cellular components of the liver microenvironment that play a central role during tumor progression. We will also discuss how current and future therapies may affect the balance toward immune activation.

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.

An OX40/OX40L interaction directs successful immunity to hepatitis B virus

Depending on age of acquisition, hepatitis B virus (HBV) can induce a cell-mediated immune response that results in either cure or progressive liver injury. In adult-acquired infection, HBV antigens are usually cleared, whereas in infancy-acquired infection, they persist. Individuals infected during infancy therefore represent the majority of patients chronically infected with HBV (CHB). A therapy that can promote viral antigen clearance in most CHB patients has not been developed and would represent a major health care advance and cost mitigator. Using an age-dependent mouse model of HBV clearance and persistence in conjunction with human blood and liver tissue, we studied mechanisms of viral clearance to identify new therapeutic targets. We demonstrate that age-dependent expression of the costimulatory molecule OX40 ligand (OX40L) by hepatic innate immune cells is pivotal in determining HBV immunity, and that treatment with OX40 agonists leads to improved HBV antigen clearance in young mice, as well as increased strength of T cell responses in young mice and adult mice that were exposed to HBV when they were young and developed a CHB serological profile. Similarly, in humans, we show that hepatic OX40L transcript expression is age-dependent and that increased OX40 expression on peripheral CD4⁺ T cells in adults is associated with HBV clearance. These findings provide new mechanistic understanding of the immune pathways and cells necessary for HBV immunity and identify potential therapeutic targets for resolving CHB.

Mononuclear phagocyte system in hepatitis C virus infection

The mononuclear phagocyte system (MPS), which consists of monocytes, dendritic cells (DCs), and macrophages, plays a vital role in the innate immune defense against pathogens. Hepatitis C virus (HCV) is efficient in evading the host immunity, thereby facilitating its development into chronic infection. Chronic HCV infection is the leading cause of end-stage liver diseases, liver cirrhosis, and hepatocellular carcinoma. Acquired immune response was regarded as the key factor to eradicate HCV. However, innate immunity can regulate the acquired immune response. Innate immunity-derived cytokines shape the adaptive immunity by regulating T-cell differentiation, which determines the outcome of acute HCV infection. Inhibition of HCV-specific T-cell responses is one of the most important strategies for immune system evasion. It is meaningful to illustrate the role of innate immune response in HCV infection. With the MPS being the important factor in innate immunity, therefore, understanding the role of the MPS in HCV infection will shed light on the pathophysiology of chronic HCV infection. In this review, we outline the impact of HCV infection on the MPS and cytokine production. We discuss how HCV is detected by the MPS and describe the function and impairment of MPS components in HCV infection.

Viral hepatitis, inflammation, and cancer: A lesson for autoimmunity

In the present review, we analyzed the various overlapping and non-mutually exclusive mechanisms that intersect and form complex and highly flexible immunological networks allowing the defense against liver infections and tumors. Liver immunity results from the combination of the skills of systemic and local immune system(s) to sense and recognize pathogen or tumor antigens, to sensitize a wide range of innate and adaptive immune cells, and to clear the "invaders", through the establishment of a transient liver immunopathology state undergoing resolution/control of infections or tumors, and memory development. Then, a special emphasis is placed on discussing about the capacity of the immune system(s) to develop a state of chronic low-level immunopathology adapting through the intervention of simultaneous immunoregulatory mechanisms, when the liver is infected by highly mutable viruses (e.g., hepatitis B or C viruses [HBV or HCV]) capable to escape from the immune recognition. The establishment of chronic inflammation represents an advantage for the species survival, because it guarantees the long-term survival of human hosts despite the virus persistence. However, chronic inflammation, in the long run, can evolve towards severe consequences (decompensated cirrhosis and hepatocellular carcinoma) in some individuals, finding requiring the impelling need of discovering new therapeutic anti-viral and immunostimulatory agents addressed, in combination, to fight especially HBV that, in contrast to HCV, lacks antivirals capable to eradicate the virus. Finally, we discussed the concept proposing that the divergent immunoregulatory mechanisms that develop in persisting infections or tumors, on the one hand, and autoimmunity, on the other hand, are the mirror image of each other, whose understanding is also relevant for preparing novel immunotherapeutic approaches in autoimmune diseases.

Hepatitis C virus-induced natural killer cell proliferation involves monocyte-derived cells and the OX40/OX40L axis

BACKGROUND & AIMS

Natural killer (NK) cells are found at increased frequencies in patients with hepatitis C virus (HCV). NK cell activation has been shown to correlate with HCV clearance and to predict a favourable treatment response. The aim of our study was to dissect mechanisms leading to NK cell activation and proliferation in response to HCV.

METHODS

NK cell phenotype, proliferation, and function were assessed after the 6-day co-culture of human peripheral blood mononuclear cells with either HCV replicon-containing HuH6 hepatoblastoma cells or HCV-infected HuH7.5 cells. The results obtained were confirmed by immunohistochemistry of liver biopsies from patients with HCV and from HCV-negative controls.

RESULTS

In HCV-containing co-cultures, a higher frequency of NK cells upregulated the expression of the high-affinity IL-2 receptor chain CD25, proliferated more rapidly, and produced higher amounts of interferon γ compared with NK cells from control co-cultures. This NK cell activation was dependent on IL-2, cell-cell contact-mediated signals, and HCV replicon-exposed monocytes. The tumour necrosis factor-receptor superfamily member OX40 was induced on the activated CD25^± NK cell subset and this induction was abrogated by the depletion of CD14⁺ monocytes. Moreover, OX40L was upregulated on CD14^± monocyte-derived cells co-cultured with HCV-containing cells and also observed in liver biopsies from patients with HCV. Importantly, blocking of the OX40/OX40L interaction abolished both NK cell activation and proliferation.

CONCLUSIONS

Our results uncover a previously unappreciated cell-cell contact-mediated mechanism of NK cell activation and proliferation in response to HCV, mediated by monocyte-derived cells and the OX40/OX40L axis. These results reveal a novel mode of crosstalk between innate immune cells during viral infection.

LAY SUMMARY

Using a cell-culture model of hepatitis C virus (HCV) infection, our study revealed that natural killer (NK) cells become activated and proliferate when they are co-cultured with HCV-containing liver cells. The mechanism of this activation involves crosstalk with other innate immune cells and a cell-cell contact interaction mediated by the cell surface molecules OX40 and OX40L. Our study reveals a novel pathway leading to NK cell proliferation and activation against virus-infected cells that might be of relevance in antiviral immunity.

OX40 Ligand Contributes to Human Lupus Pathogenesis by Promoting T Follicular Helper Response

Increased activity of T follicular helper (Tfh) cells plays a major pathogenic role in systemic lupus erythematosus (SLE). However, the mechanisms that cause aberrant Tfh cell responses in SLE remain elusive. Here we showed the OX40 ligand (OX40L)-OX40 axis contributes to the aberrant Tfh response in SLE. OX40L was expressed by myeloid antigen-presenting cells (APCs), but not B cells, in blood and in inflamed tissues in adult and pediatric SLE patients. The frequency of circulating OX40L-expressing myeloid APCs positively correlated with disease activity and the frequency of ICOS(+) blood Tfh cells in SLE. OX40 signals promoted naive and memory CD4(+) T cells to express multiple Tfh cell molecules and were sufficient to induce them to become functional B cell helpers. Immune complexes containing RNA induced OX40L expression on myeloid APCs via TLR7 activation. Our study provides a rationale to target the OX40L-OX40 axis as a therapeutic modality for SLE.

Basophil-associated OX40 ligand participates in the initiation of Th2 responses during airway inflammation

Asthma is characterized by increased airway submucosal infiltration of T helper (Th) cells and myeloid cells that co-conspire to sustain a chronic inflammation. While recent studies have demonstrated that the myeloid basophils promote Th2 cells in response to various types of allergens, the underlying mechanisms are poorly understood. Here, we found for the first time that in a mouse model of allergic asthma basophils highly expressed OX40 ligand (OX40L) after activation. Interestingly, blockade of OX40-OX40L interaction suppressed basophils-primed Th2 cell differentiation in vitro and ameliorated ovalbumin (OVA)-induced allergic eosinophilic inflammation mediated by Th2 activation. In accordance, the adoptive transfer of basophils derived from mediastinal lymph nodes (MLN) of OVA-immunized mice triggered a robust Th2 response and eosinophilic inflammation in wild-type mice but largely muted in OX40(-/-) mice and mice receiving OX40L-blocked basophils. Taken together, our results reveal a critical role of OX40L presented by the activated basophils to initiate Th2 responses in an allergic asthma model, implicating OX40-OX40L signaling as a potential therapeutic target in the treatment of allergic airway inflammation.

CD100 up-regulation induced by interferon-α on B cells is related to hepatitis C virus infection

Objectives

CD100, also known as Sema4D, is a member of the semaphorin family and has important regulatory functions that promote immune cell activation and responses. The role of CD100 expression on B cells in immune regulation during chronic hepatitis C virus (HCV) infection remains unclear.

Materials and Methods

We longitudinally investigated the altered expression of CD100, its receptor CD72, and other activation markers CD69 and CD86 on B cells in 20 chronic HCV-infected patients before and after treatment with pegylated interferon-alpha (Peg-IFN-α) and ribavirin (RBV) by flow cytometry.

Results

The frequency of CD5⁺ B cells as well as the expression levels of CD100, CD69 and CD86 was significantly increased in chronic HCV patients and returned to normal in patients with sustained virological response after discontinuation of IFN-α/RBV therapy. Upon IFN-α treatment, CD100 expression on B cells and the two subsets was further up-regulated in patients who achieved early virological response, and this was confirmed by in vitro experiments. Moreover, the increased CD100 expression via IFN-α was inversely correlated with the decline of the HCV-RNA titer during early-phase treatment.

Conclusions

Peripheral B cells show an activated phenotype during chronic HCV infection. Moreover, IFN-α therapy facilitates the reversion of disrupted B cell homeostasis, and up-regulated expression of CD100 may be indirectly related to HCV clearance.

Human OX40 tunes the function of regulatory T cells in tumor and nontumor areas of hepatitis C virus-infected liver tissue

Regulatory T cells (Tregs) can be considered as a mixed population of distinct subsets, endowed with a diverse extent and quality of adaptation to microenvironmental signals. Here, we uncovered an opposite distribution of Treg expansion, phenotype, and plasticity in different microenvironments in the same organ (liver) derived from patients with chronic hepatitis C: On the one side, cirrhotic and tumor fragments were moderately and highly infiltrated by Tregs, respectively, expressing OX40 and a T-bethigh IFN-γ- "T-helper (Th)1-suppressing" phenotype; on the other side, noncirrhotic liver specimens contained low frequencies of Tregs that expressed low levels of OX40 and highly produced interferon-gamma (IFN-γ; T-bet+IFN-γ+), thus becoming "Th1-like" cells. OX40-expressing and Th1-suppressing Tregs were enriched in the Helios-positive subset, carrying highly demethylated Treg cell-specific demethylated region that configures committed Tregs stably expressing forkhead box protein 3. OX40 ligand, mostly expressed by M2-like monocytes and macrophages, boosted OX40+ Treg proliferation and antagonized the differentiation of Th1-like Tregs. However, this signal is counteracted in noncirrhotic liver tissue (showing various levels of inflammation) by high availability of interleukin-12 and IFN-γ, ultimately leading to complete, full Th1-like Treg differentiation.

CONCLUSION

Our data demonstrate that Tregs can finely adapt, or even subvert, their classical inhibitory machinery in distinct microenvironments within the same organ.