Profiles of NK, NKT cell activation and cytokine production following vaccination against hepatitis B

Durable natural killer cell response after three doses of SARS-CoV-2 inactivated vaccine in HIV-infected individuals

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine can induce a potent cellular and humoral immune response to protect against SARS-CoV-2 infection. However, it was unknown whether SARS-CoV-2 vaccination can induce effective natural killer (NK) cell response in people living with human immunodeficiency virus (PLWH) and healthy individuals.

METHODS

Forty-seven PLWH and thirty healthy controls (HCs) inoculated with SARS-CoV-2 inactivated vaccine were enrolled from Beijing Youan Hospital in this study. The effect of SARS-CoV-2 vaccine on NK cell frequency, phenotype, and function in PLWH and HCs was evaluated by flow cytometry, and the response of NK cells to SARS-CoV-2 Omicron Spike (SARS-2-OS) protein stimulation was also evaluated.

RESULTS

SARS-CoV-2 vaccine inoculation elicited activation and degranulation of NK cells in PLWH, which peaked at 2 weeks and then decreased to a minimum at 12 weeks after the third dose of vaccine. However, in vitro stimulation of the corresponding peripheral blood monocular cells from PLWH with SARS-2-OS protein did not upregulate the expression of the aforementioned markers. Additionally, the frequencies of NK cells expressing the activation markers CD25 and CD69 in PLWH were significantly lower than those in HCs at 0, 4 and 12 weeks, but the percentage of CD16 + NK cells in PLWH was significantly higher than that in HCs at 2, 4 and 12 weeks after the third dose of vaccine. Interestingly, the frequency of CD16 + NK cells was significantly negatively correlated with the proportion of CD107a + NK cells in PLWH at each time point after the third dose. Similarly, this phenomenon was also observed in HCs at 0, 2, and 4 weeks after the third dose. Finally, regardless of whether NK cells were stimulated with SARS-2-OS or not, we did not observe any differences in the expression of NK cell degranulation markers between PLWH and HCs.

CONCLUSION

s:SARS-CoV-2 vaccine elicited activation and degranulation of NK cells, indicating that the inoculation of SARS-CoV-2 vaccine enhances NK cell immune response.

Natural Killer T-like Cells: Immunobiology and Role in Disease

CD56+ T cells are generally recognized as a distinct population of T cells and are categorized as NKT-like cells. Although our understanding of NKT-like cells is far from satisfactory, it has been shown that aging and a number of disease situations have impacted these cells. To construct an overview of what is currently known, we reviewed the literature on human NKT-like cells. NKT-like cells are highly differentiated T cells with "CD1d-independent" antigen recognition and MHC-unrestricted cell killing. The genesis of NKT-like cells is unclear; however, it is proposed that the acquisition of innate characteristics by T cells could represent a remodeling process leading to successful aging. Additionally, it has been shown that NKT-like cells may play a significant role in several pathological conditions, making it necessary to comprehend whether these cells might function as prognostic markers. The quantification and characterization of these cells might serve as a cutting-edge indicator of individual immune health. Additionally, exploring the mechanisms that can control their killing activity in different contexts may therefore result in innovative therapeutic alternatives in a wide range of disease settings.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

HBsAg stimulates NKG2D receptor expression on natural killer cells and inhibits hepatitis C virus replication

BACKGROUND

Higher hepatitis B surface antigen (HBsAg) facilitates hepatitis C virus (HCV) clearance in patients with hepatitis B virus (HBV)/HCV co-infection. We investigated the effect of exogenous HBsAg on the inhibition of HCV replication mediated by natural killer (NK) cells.

METHODS

After isolated from peripheral blood of 42 chronic hepatitis B (CHB) patients and 16 healthy individuals, NK cells were co-cultured with HCV-infected Huh7 cells, respectively, with or without HBsAg. Three days later, the co-cultured supernatants were collected and HCV RNA levels were measured by real-time quantitative PCR. NKG2D, NKp46 and NKG2A expression levels were measured by flow cytometry. NKG2D on NK cells from CHB responsive subgroup was blocked and HCV RNA levels were examined again.

RESULTS

HCV RNA levels in the co-cultured system were significantly reduced by NK cells isolated from healthy donors (P < 0.01) but not from CHB patients. However, HCV RNA levels in CHB cultures were significantly decreased following HBsAg addition (P < 0.05), whereas no such effect was seen in control cultures. No significant difference was observed in basic NKG2D expression between the CHB patients and healthy donors. On NK cells from CHB patients, the expression of NKG2D was increased significantly by HBsAg stimulation (P < 0.01), and higher than that from healthy controls (P < 0.05). HCV RNA levels were increased significantly after the blockage of NKG2D on NK cells from responsive CHB patients in the co-cultured system (P < 0.05).

CONCLUSION

Exogenous HBsAg stimulated NKG2D expression on NK cells from CHB patients which inhibit HCV replication, suggesting that HBsAg may facilitate the clearance of HCV in patients with HBV/HCV co-infection.

Current concepts on immunopathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) infection is a leading cause of liver damage and hepatic inflammation. Upon infection, effective antiviral responses by CD8+ T cells, CD4+ T cells, Natural killer (NK) cells, and monocytes can lead to partial or complete eradication of the viral infection. To date, many studies have shown that the production of inhibitory cytokines such as Interleukin 10 (IL-10), Transforming growth factor beta (TGF-β), along with dysfunction of the dendritic cells (DCs), and the absence of efficient innate immune responses could lead to T cell exhaustion, development of persistent infection, and inability to eradicate the viral infection from liver. Understanding the immunopathogenesis of the virus could be useful in providing further insights toward novel strategies in the eradication of HBV infection.

Chain length-dependent effects of inulin-type fructan dietary fiber on human systemic immune responses against hepatitis-B

SCOPE

In vivo studies demonstrating that only specific dietary-fibers contribute to immunity are still inconclusive, as measuring immune effects in healthy humans remains difficult. We applied a relatively inefficacious vaccination-challenge to study chain length-dependent effects of inulin-type fructan (ITF) dietary fibers on human immunity.

METHODS AND RESULTS

ITFs with two different 'degree of polymerization-' (DP)-profiles were tested in vitro for effects on PBMC-cytokines and TLR2 activation. In a double-blind placebo-controlled trial, 40 healthy volunteers (18-29 years) were divided into three groups and supplemented from day 1 to day 14 with DP10-60 ITF, DP2-25 ITF (both n = 13), or fructose placebo (n = 14), 8 g/day. On day 7, all volunteers were vaccinated against hepatitis B. Anti-HbsAg-titer development and lymphocyte subsets were studied. In vitro, DP10-60 ITFs stimulated a Th1-like cytokine profile and stimulated TLR2 more strongly than DP2-25 ITFs. In vivo, DP10-60 increased anti-HBsAg titers, Th1-cells, and transitional B-cells. Both ITFs increased CD45RO^hi CTLs at day 35, and CD161⁺ cytokine producing NK-cells at day 21 and 35.

CONCLUSION

Support of immunity is determined by the chain length of ITFs. Only long-chain ITFs support immunity against pathogenic hepB-epitopes introduced by vaccination. Our findings demonstrate that specific dietary fibers need to be selected for immunity support.

Altered T cell phenotypes associated with clinical relapse of multiple sclerosis patients receiving fingolimod therapy

Multiple sclerosis (MS) is a T cell-mediated autoimmune disease. Fingolimod, a highly effective disease-modifying drug for MS, retains CCR7⁺ central memory T cells in which autoaggressive T cells putatively exist, in secondary lymphoid organs, although relapse may still occur in some patients. Here, we analyzed the T cell phenotypes of fingolimod-treated, fingolimod-untreated patients, and healthy subjects. The frequency of CD56⁺ T cells and granzyme B-, perforin-, and Fas ligand-positive T cells significantly increased during fingolimod treatment. Each T cell subpopulation further increased during relapse. Interestingly, T cells from fingolimod-treated patients exhibited interferon-γ biased production, and more myelin basic protein-reactive cells was noted in CD56⁺ than in CD56⁻ T cells. It is likely that the altered T cell phenotypes play a role in MS relapse in fingolimod-treated patients. Further clinical studies are necessary to investigate whether altered T cell phenotypes are a biomarker for relapse under fingolimod therapy.

Roles of acetylation-dependent regulation in pathogenesis of chronic hepatitis B virus infection: Potential application as targets for antiviral treatment

In recent years, many studies have confirmed that epigenetics and acetylation-dependent regulation play important roles in the pathogenesis of chronic hepatitis and primary hepatocellular carcinoma. This paper systematically introduces the roles and possible mechanisms of acetylation and its related signal pathways in the pathogenesis of chronic hepatitis B virus (HBV) infection, which may provide a potential novel strategy for the therapy of chronic HBV infection.

Hepatitis B virus antigens impair NK cell function

An inadequate immune response of the host is thought to be a critical factor causing chronic hepatitis B virus (CHB) infection. Natural killer (NK) cells, as one of the key players in the eradication and control of viral infections, were functionally impaired in CHB patients, which might contribute to viral persistence. Here, we reported that HBV antigens HBsAg and HBeAg directly inhibited NK cell function. HBsAg and/or HBeAg blocked NK cell activation, cytokine production and cytotoxic granule release in human NK cell-line NK-92 cells, which might be related to the downregulation of activating receptors and upregulation of inhibitory receptor. Furthermore, the underlying mechanisms likely involved the suppression of STAT1, NF-κB and p38 MAPK pathways. These findings implicated that HBV antigen-mediated inhibition of NK cells might be an efficient strategy for HBV evasion, targeting the early antiviral responses mediated by NK cells and resulting in the establishment of chronic virus infection. Therefore, this study revealed the relationship between viral antigens and human immune function, especially a potential important interaction between HBV and innate immune responses.

Immunogenicity and mechanisms impairing the response to vaccines in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an immunological disorder that is usually treated with immunosuppressive therapy, potentially leading to increases in vulnerability to infections. Although many infections can be prevented by vaccination, vaccination coverage in these patients in clinical practice is insufficient. Therefore, the seroprotection condition should be verified, even for routine vaccines, such as hepatitis B or pneumococcus. Response to vaccines in IBD patients is thought to be impaired due to the immunological alterations generated by the disease and to the immunomodulatory treatments. The immunogenicity of hepatitis B, influenza, and pneumococcal vaccines is impaired in IBD patients, whereas the response to papillomavirus vaccine seems similar to that observed in the healthy population. On the other hand, data on the immunogenicity of tetanus vaccine in IBD patients are conflicting. Studies assessing the response to measles-mumps-rubella, varicella, and herpes zoster vaccines in IBD patients are scarce. The cellular and molecular mechanisms responsible for the impairment of the response to vaccination in IBD patients are poorly understood. Studies aiming to assess the response to vaccines in IBD patients and to identify the mechanisms involved in their immunogenicity are warranted. A better understanding of the immune response, specifically to vaccines, in patients with immune-mediated diseases (such as IBD), is crucial when developing vaccines that trigger more potent immunologic responses.

Circulating CD56dim natural killer cells and CD56+ T cells that produce interferon-γ or interleukin-10 are expanded in asymptomatic, E antigen-negative patients with persistent hepatitis B virus infection

Infection with hepatitis B virus (HBV) can result in spontaneous resolution or chronic infection, which can remain asymptomatic or can progress to cirrhosis and/or hepatocellular carcinoma. The host immune response is thought to be a major determinant of the outcome of HBV infection and virus-specific cytotoxic T lymphocytes (CTL) can mediate immunity against the virus and cause liver pathology. Antigen-nonspecific innate lymphocytes may also contribute to HBV infection and liver disease, therefore, we examined the frequencies, phenotypes, cytolytic activities and cytokine profiles of circulating natural killer (NK) cells, CD1d-restricted invariant natural killer T (iNKT) cells and CD56(+) T cells in 102 asymptomatic HBV-infected patients and compared them with those in 66 uninfected control subjects. NK cells expressing low levels of CD56 (CD56(dim)) and CD56(+) T cells were significantly expanded in the circulation of HBV-infected patients compared with control subjects. CD1d expression and iNKT cell frequencies were similar in both groups. Despite these expansions, we did not detect augmented natural or cytokine-induced cytotoxicity in the HBV-infected subjects. All lymphocyte populations studied produced interferon-γ (IFN-γ) significantly more frequently when taken from HBV-infected patients compared with when taken from healthy controls. Additionally, NK cells from the patients more frequently produced interleukin-10. As our HBV-infected cohort consisted of asymptomatic patients with low viral loads, we propose that CD56(dim) NK cells and CD56(+) T cells control HBV infection by noncytolytic mechanisms.

Innate immune responses in hepatitis B virus (HBV) infection

Hepatitis B virus (HBV) infection has a low rate of chronicity compared to HCV infection, but chronic liver inflammation can evolve to life threatening complications. Experimental data from HBV infected chimpanzees and HBV transgenic mice have indicated that cytotoxic T cells are the main cell type responsible for inhibition of viral replication, but also for hepatocyte lysis during chronic HBV infection. Their lower activation and impaired function in later stages of infection was suggested as a possible mechanism that allowed for low levels of viral replication. The lack of an interferon response in these models also indicated the importance of adaptive immunity in clearing the infection. Increased knowledge of the signalling pathways and pathogen associated molecular patterns that govern activation of innate immunity in the early stages of viral infections in general has led to a re-evaluation of the innate immune system in HBV infection. Numerous studies have shown that HBV employs active strategies to evade innate immune responses and induce immunosuppression. Some of the immune components targeted by HBV include dendritic cells, natural killer cells, T regulatory cells and signalling pathways of the interferon response. This review will present the current understanding of innate immunity in HBV infection and of the challenges associated with clearing of the HBV infection.

IFNG and IFNGR1 gene polymorphisms in children with nonresponse to the hepatitis B vaccine

ABSTRACT: 

Aim: We investigated the +874 T/A polymorphism in the first intron of the IFNG gene and intronic (CA)n polymorphic microsatellite marker of the IFNGR 1 gene in child nonresponders to hepatitis B vaccination. Materials & methods: A total of 100 children who had anti-HBs antibody levels <10 mIU/ml after vaccination against hepatitis B were included as a nonresponder group and 100 children who had anti-HBs antibody levels >10 mIU/ml after vaccination against hepatitis B were included as a responder group. Results: The frequency of the TT genotype of the IFNG (+874 T/A) gene polymorphism was higher in nonresponders (p = 0.003). The frequencies of alleles 170 and 182 for (CA)n alleles for the intronic (CA)n microsatellite of IFNGR1 were significantly higher in nonresponders (for each, p < 0.05). Conclusion: The TT genotype of the IFNG (+874 T/A) gene, and alleles 170 and 182 for (CA)n alleles for the intronic (CA)n microsatellite of the IFNGR1 gene, may be associated with nonresponse to hepatitis B vaccination.

KLRG1 impairs CD4+ T cell responses via p16ink4a and p27kip1 pathways: role in hepatitis B vaccine failure in individuals with hepatitis C virus infection

Coinfection of hepatitis B virus (HBV) with hepatitis C virus (HCV) is quite common, leading to an increase in morbidity and mortality. As such, HBV vaccination is recommended in HCV-infected individuals. However, HBV vaccine responses in HCV-infected individuals are often blunted compared with uninfected populations. The mechanism for this failure of vaccine response in HCV-infected subjects remains unclear. In this study, we investigated the expression and function of an inhibitory receptor, killer cell lectin-like receptor subfamily G member 1 (KLRG1), in the regulation of CD4(+) T cells and HBV vaccine responses during HCV infection. We demonstrated that KLRG1 was overexpressed on CD4(+) T cells from HCV-infected, HBV vaccine nonresponders compared with HBV vaccine responders. The capacity of CD4(+) T cells to proliferate and secrete IL-2 cytokine was inversely associated with the level of KLRG1 expression. Importantly, blocking KLRG1 signaling resulted in a significant improvement in CD4(+) T cell proliferation and IL-2 production in HCV-infected, HBV vaccine nonresponders in response to TCR stimulation. Moreover, blockade of KLRG1 increased the phosphorylation of Akt (Ser(473)) and decreased the expression of cell cycle inhibitors p16(ink4a) and p27(kip1), which subsequently enhanced the expression of cyclin-dependent kinase 2 and cyclin E. These results suggest that the KLRG1 pathway impairs CD4(+) T cell responses to neoantigen and induces a state of immune senescence in individuals with HCV infection, raising the possibility that blocking this negative-signaling pathway might improve HBV vaccine responses in the setting of chronic viral infection.

Immune exhaustion and immune senescence: two distinct pathways for HBV vaccine failure during HCV and/or HIV infection

Given the shared risk factors for transmission, co-infection of hepatitis B virus (HBV) with hepatitis C virus (HCV) and/or human immunodeficiency virus (HIV) is quite common, and may lead to increases in morbidity and mortality. As such, HBV vaccine is recommended as the primary means to prevent HBV super-infection in HCV- and/or HIV-infected individuals. However, vaccine response (sero-conversion with a hepatitis B surface antibody titer >10 IU/L) in this setting is often blunted, with poor response rates to standard HBV vaccinations in virally infected individuals when compared with the healthy subjects. This phenomenon also occurs to other vaccines in adults, such as pneumococcal and influenza vaccines, in other immunocompromised hosts who are really at risk for opportunistic infections, such as individuals with hemodialysis, transplant, and malignancy. In this review, we summarize the underlying mechanisms involving vaccine failure in these conditions, focusing on immune exhaustion and immune senescence--two distinct signaling pathways regulating cell function and fate. We raise the possibility that blocking these negative signaling pathways might improve success rates of immunizations in the setting of chronic viral infection.

Tim-3 alters the balance of IL-12/IL-23 and drives TH17 cells: role in hepatitis B vaccine failure during hepatitis C infection

Hepatitis B virus (HBV) vaccination is recommended for individuals with hepatitis C virus (HCV) infection given their shared risk factors and increased liver-related morbidity and mortality upon super-infection. Vaccine responses in this setting are often blunted, with poor response rates to HBV vaccinations in chronically HCV-infected individuals compared to healthy subjects. In this study, we investigated the role of T cell immunoglobulin mucin domain-3 (Tim-3)-mediated immune regulation in HBV vaccine responses during HCV infection. We found that Tim-3, a marker for T cell exhaustion, was over-expressed on monocytes, leading to a differential regulation of IL-12/IL-23 production which in turn TH17 cell accumulation, in HCV-infected HBV vaccine non-responders compared to HCV-infected HBV vaccine responders or healthy subjects (HS). Importantly, ex vivo blockade of Tim-3 signaling corrected the imbalance of IL-12/IL-23 as well as the IL-17 bias observed in HBV vaccine non-responders during HCV infection. These results suggest that Tim-3-mediated dysregulation of innate to adaptive immune responses is involved in HBV vaccine failure in individuals with chronic HCV infection, raising the possibility that blocking this negative signaling pathway might improve the success rate of HBV immunization in the setting of chronic viral infection.

Hepatitis B surface antigen could contribute to the immunopathogenesis of hepatitis B virus infection

Various findings concerning the clinical significance of quantitative changes in hepatitis B surface antigen (HBsAg) during the acute and chronic phase of hepatitis B virus (HBV) infection have been reported. In addition to being a biomarker of HBV-replication activity, it has been reported that HBsAg could contribute to the immunopathogenesis of HBV persistent infection. Moreover, HBsAg could become an attractive target for immune therapy, since the cellular and humeral immune response against HBsAg might be able to control the HBV replication and life cycle. However, several reports have described the immune suppressive function of HBsAg. HBsAg might suppress monocytes, dendritic cells (DCs), natural killer (NK), and natural killer T (NK-T) cells by direct interaction. On the other hand, cytotoxic T lymphocytes (CTLs) and helper T (Th) cells were exhausted by high amounts of HBsAg. In this paper, we focused on the immunological aspects of HBsAg, since better understanding of the interaction between HBsAg and immune cells could contribute to the development of an immune therapy as well as a biomarker of the state of HBV persistent infection.

Activated lymphocytes and high liver expression of IFN-γ are associated with fulminant hepatic failure in patients

BACKGROUND & AIMS

To study immunological mechanisms of fulminant hepatic failure (FHF) derived from extensive liver lesions, 14 patients with FHF induced by different aetiologies were investigated by observance of both lymphocyte phenotyping and cytokine levels.

METHODS

Five patients bearing benign acute hepatitis B (AHB) and seven healthy liver donors (HC) were used as controls. Samples of liver and blood from both FHF patients and HC were obtained during transplantation procedures. Plasma levels of IL-1β, IL-4, IL-6, IL-8, IL-10, IFN-γ, TNF-α, MCP-1, RANTES and MIP-1α were quantified using a multiplex immunoassay. Cell characterization was carried out by flow cytometry. IFN-γ staining was performed on liver sections using immunofluorescence methods.

RESULTS

An increase of peripheral frequency of natural killer (NK) cells expressing early activation markers (CD69, HLA-DR and CD38) and adhesion molecule CD44 was observed in FHF patients. Elevated frequency of T lymphocytes CD4(+) and CD8(+) expressing CD38 and adhesion molecules CD29 and CD44 was also observed in FHF. Additionally, an increase of natural killer T cells (NKT) was detected in FHF patients. High plasma cytokine levels were not statistically different between FHF and AHB patients. In comparison to HC, a strong liver expression of IFN-γ was detected in FHF patients. The increased frequency of CD4(+) CD44(+) and IL-8 cytokine was found in patients with poor prognosis.

CONCLUSIONS

These findings indicate the involvement of NK and NKT cells as well as T lymphocytes CD4(+) and CD8(+) in the inflammatory process inducing FHF, confirmed by the high hepatic expression of IFN-γ.

Virus stimulation of human mast cells results in the recruitment of CD56⁺ T cells by a mechanism dependent on CCR5 ligands

The trafficking of effector cells to sites of infection is crucial for antiviral responses. However, the mechanisms of recruitment of the interferon-γ-producing and cytotoxic CD56(+) T cells are poorly understood. Human mast cells are sentinel cells found in the skin and airway and produce selected proinflammatory mediators in response to multiple pathogen-associated signals. The role of human mast cell-derived chemokines in T-cell recruitment to virus infection was examined. Supernatants from primary human cord blood-derived mast cells (CBMCs) infected with mammalian reovirus were examined for chemokine production and utilized in chemotaxis assays. Virus-infected CBMCs produced several chemokines, including CCL3, CCL4, and CCL5. Supernatants from reovirus-infected CBMCs selectively induced the chemotaxis of CD8(+) T cells (10±1%) and CD3(+)CD56(+) T cells (19±5%). CD56(+) T-cell migration was inhibited by pertussis toxin (65±9%) and met-RANTES (56±7%), a CCR1/CCR5 antagonist. CD56(+) T cells expressed CCR5, but little CCR1. The depletion of CCL3, CCL4, and CCL5 from reovirus-infected CBMC supernatants significantly (41±10%) inhibited CD56(+) T-cell chemotaxis. This study demonstrates a novel role for mast cells and CCR5 in CD56(+) T-cell trafficking and suggests that human mast cells enhance immunity to viruses through the selective recruitment of cytotoxic effector cells to virus infection sites. These findings could be exploited to enhance local T-cell responses in chronic viral infection and malignancies at mast cell-rich sites.

Targeting the diverse immunological functions expressed by hepatic NKT cells

INTRODUCTION

NKT cells comprise approximately 30% of the hepatic lymphoid population in mice (∼ 50% in humans). Most mouse hepatic NKT cells [invariant (i)NKT cells] express T cell receptors, composed of invariant Vα14Jα18 chains. Unlike conventional T cells, iNKT cells recognize glycolipids presented in association with MHC class Ib (CD1d) molecules. Purportedly, iNKT cells serve key functions in several immunological events; the nature of these is often unclear. The consequences of hepatic iNKT cell activation can be beneficial or detrimental. α-Galactosylceramide stimulates the production of IFN-γ and IL-4. The reciprocal suppression exhibited by these cytokines limits the potential therapeutic value of α-galactosylceramide. Efforts are ongoing to develop α-galactosylceramide analogs that modulate iNKT cell activity and selectively promote IFN-γ or IL-4.

AREAS COVERED

An overview of hepatic iNKT cells and their purported role in liver disease. Efforts to develop therapeutic agents that promote their beneficial contributions.

EXPERT OPINION

While a growing body of literature documents the differential effects of α-GalCer analogs on IFN-γ and IL-4 production, the effects of these analogs on other iNKT cell activities remain to be determined. An exhaustive examination of the effects of these analogs on inflammation and liver injury in animal models remains prior to considering their utility in clinical trials.

Impaired hepatitis B vaccine responses during chronic hepatitis C infection: involvement of the PD-1 pathway in regulating CD4(+) T cell responses

Vaccination for hepatitis B virus (HBV) in the setting of hepatitis C virus (HCV) infection is recommended, but responses to vaccination are blunted when compared to uninfected populations. The mechanism for this failure of immune response in HCV-infected subjects remains unknown but is thought to be a result of lymphocyte dysfunction during chronic viral infection. We have recently demonstrated that PD-1, a novel negative immunomodulator for T cell receptor (TCR) signaling, is involved in T and B lymphocyte dysregulation during chronic HCV infection. In this report, we further investigated the role of the PD-1 pathway in regulation of CD4(+) T cell responses to HBV vaccination in HCV-infected individuals. In a prospective HCV infected cohort, a poor response rate to HBV vaccination as assayed by seroconversion was observed in HCV-infected subjects (53%), while a high response rate was observed in healthy or spontaneously HCV-resolved individuals (94%). CD4(+) T cell responses to ex vivo stimulations of anti-CD3/CD28 antibodies or hepatitis B surface antigen (HBsAg) were found to be lower in HBV vaccine non-responders compared to those responders in HCV-infected individuals who had received a series of HBV immunizations. PD-1 expression on CD4(+) T cells was detected at relatively higher levels in these HBV vaccine non-responders than those who responded, and this was inversely associated with the cell activation status. Importantly, blocking the PD-1 pathway improved T cell activation and proliferation in response to ex vivo HBsAg or anti-CD3/CD28 stimulation in HBV vaccine non-responders. These results suggest that PD-1 signaling may be involved in impairing CD4(+) T cell responses to HBV vaccination in subjects with HCV infection, and raise the possibility that blocking this negative signaling pathway might improve success rates of immunization in the setting of chronic viral infection.

Innate lymphocyte and dendritic cell cross-talk: a key factor in the regulation of the immune response

Dendritic cells (DC) are specialized in the presentation of antigens and the initiation of specific immune responses. They have been involved recently in supporting innate immunity by interacting with various innate lymphocytes, such as natural killer (NK), NK T or T cell receptor (TCR)-gammadelta cells. The functional links between innate lymphocytes and DC have been investigated widely and different studies demonstrated that reciprocal activations follow on from NK/DC interactions. The cross-talk between innate cells and DC which leads to innate lymphocyte activation and DC maturation was found to be multi-directional, involving not only cell-cell contacts but also soluble factors. The final outcome of these cellular interactions may have a dramatic impact on the quality and strength of the down-stream immune responses, mainly in the context of early responses to tumour cells and infectious agents. Interestingly, DC, NK and TCR-gammadelta cells also share similar functions, such as antigen uptake and presentation, as well as cytotoxic and tumoricidal activity. In addition, NK and NK T cells have the ability to kill DC. This review will focus upon the different aspects of the cross-talk between DC and innate lymphocytes and its key role in all the steps of the immune response. These cellular interactions may be particularly critical in situations where immune surveillance requires efficient early innate responses.

Hepatic NKT cells: friend or foe?

The innate immune system represents a critical first line of host response to infectious, injurious and inflammatory insults. NKT cells (natural killer T-cells) are an important, but relatively poorly understood, component of the innate immune response. Moreover, NKT cells are enriched within the liver, suggesting that within the hepatic compartment NKT cells probably fulfil important roles in the modulation of the immune response to infection or injury. NKT cells are characterized by their rapid activation and secretion of large amounts of numerous types of cytokines, including those within the Th1-type, Th2-type and Th17-type groups, which in turn can interact with a multitude of other cell types within the liver. In addition, NKT cells are capable of participating in a wide array of effector functions with regards to other cell types via NKT cell-surface-molecule expression [e.g. FASL (FAS ligand) and CD40L (CD40 ligand)] and the release of mediators (e.g. perforin and granzyme) contained in cellular granules, which in turn can activate or destroy other cells (i.e. immune or parenchymal cells) within the liver. Given the huge scope of potential actions that can be mediated by NKT cells, it has become increasingly apparent that NKT cells may fulfil both beneficial (e.g. clearance of virally infected cells) and harmful (e.g. induction of autoimmunity) roles in the setting of liver disease. This review will outline the possible roles which may be played by NKT cells in the setting of specific liver diseases or conditions, and will discuss the NKT cell in the context of its role as either a ‘friend’ or a ‘foe’ with respect to the outcome of these liver disorders.

Decrease in CD4+ T lymphocyte proliferation responses and enhanced CD150 cell expression in health care workers non-responsive to HBV vaccine

The non-response to hepatitis B vaccine in health care workers (HCWs) is reported to vary between 5 and 40%. The underlying cellular and molecular events for unresponsiveness to HBV vaccine have not yet been characterized at any great extent. In the current study, we examined the CD150 surface expression levels and its association with polyclonally activated and HBV specific stimulated cellular proliferations in responders and non-responders. CD150 was identified as upregulated expression marker with suppressive regulatory cell function on all activated T cells by gene chip analysis. We found the overall weak cellular proliferation in response to specific and non-specific agents in non-responders. This is significantly associated with enhanced surface expression of CD150 in the non-responders. A strong expression of CD150 with weak cellular proliferation could be used as a predictive marker for non-responsiveness.