Negative regulation of NK cell activities by inhibitory receptor CD94/NKG2A leads to altered NK cell-induced modulation of dendritic cell functions in chronic hepatitis C virus infection

NKG2A and CD56 are coexpressed on activated TH2 but not TH1 lymphocytes

NKG2A is commonly expressed on cytotoxic cells but has been found on activated T helper (TH) cells. In identifying novel markers differentiating between TH1 and TH2 lymphocytes, we focused on NKG2A expression. TH1 and TH2 cells were negatively isolated from healthy volunteers for microarray analysis and reverse transcription polymerase chain reaction (RT-PCR). Flow cytometry of quiescent and activated TH1 and TH2 cells was performed. Isolates were >95% pure CD3+CD4+ cells (TH1=90.3% and TH2=84.1%). Microarrays revealed differential expression of NKG2A and NKG2C isoforms between TH1 and TH2 cells. RT-PCR indicated greater expression of NKG2A in TH2 cells (4-fold) and NKG2C in TH1 cells (3-fold). Flow studies revealed tripling of TH2 NKG2A with activation to 10.76+/-4.01% (p=0.05), a 23-fold increase in CD56 to 35+/-14.54% (p=0.03), and an increase in NKG2A+CD56+ double-positive cells to 3.04+/-1.38% (p=0.04). TH1 lymphocytes did not differ with activation. We identified co-induction of NKG2A and CD56 on activation of TH2 cells. These cells would likely bind more HLA-E and exhibit increased effector inhibition. Given that certain viruses are known to decrease MHC class I and thus HLA-E production by antigen-presenting cells, activated TH2 cells would bind less HLA-E in this scenario. This would likely result in less effector inhibition and a relatively robust TH2 response.

Impairment of natural killer cell and dendritic cell functions by the soluble form of MHC class I-related chain A in advanced human hepatocellular carcinomas

BACKGROUND/AIMS

MHC class I-related chain A (MICA), a human ligand of natural killer (NK) cell stimulatory receptor NKG2D, is expressed in human hepatocellular carcinomas (HCC). Earlier research demonstrated that the soluble form of MICA (sMICA) is released from some types of tumors, but its presence and role in HCC was not determined.

METHODS

Serum sMICA was studied in 26 patients with HCC. In vitro experiments were performed to examine the impact of sMICA on NK cell expression of NKG2D and subsequent dendritic cell (DC) activation.

RESULTS

The levels of sMICA were frequently elevated in patients with advanced HCC. The elevation of sMICA was associated with down-regulated NKG2D expression and impaired activation of NK cells. In vitro experiments revealed that sMICA derived from advanced HCC was responsible for down-modulation of NKG2D expression and NK cell functions. NK cells upon stimulation of human hepatoma cells induced maturation of DC and enhanced the allostimulatory capacity of DC; maturation and activation of DC were completely abolished when NK cells were pre-treated with sMICA-containing serum.

CONCLUSIONS

sMICA is present in sera of patients with advanced HCC and may serve as a tumor evasion mechanism by negatively modulating both innate and adaptive immunity.

He Jie Tang in the treatment of chronic hepatitis B patients

AIM: To explore the effect of He Jie Tang (decoction for medication) on serum levels of T lymphocyte subsets, NK cell activity and cytokines in chronic hepatitis B patients.

METHODS: Eighty-five patients with chronic hepatitis B were divided randomly into two groups. Fifty patients in group I were treated with He Jie Tang (HJT) and 35 patients in group II were treated with combined medication. The levels of T-lymphocyte subsets (CD₃⁺, CD₄⁺, CD₈⁺), NK cell activity, cytokines (TNF-α, IL-8, sIL-2R) were observed before and after the treatment. Another 20 normal persons served as group 3.

RESULTS: The level of CD₄⁺ cells and NK cell activity were lower, whereas the level of CD₈⁺ cells in patients was higher than that in normal persons (t = 2.685, 3.172, and 2.754 respectively; P<0.01). The levels of TNF-α, IL-8, and sIL-2R in chronic hepatitis B patients were higher than those in normal persons (t = 3.526, 3.170, and 2.876 respectively; P<0.01). After 6 months of treatment, ALT, AST, and TB levels in the two groups were obviously decreased (t = 3.421, 3.106, and 2.857 respectively; P<0.01). The level of CD₄⁺ cells and NK cell activity were increased whereas the level of CD₈⁺ cells decreased (t = 2.179, 2.423, and 2.677 respectively; P<0.05) in group I. The levels of TNF-α, IL-8, and sIL-2R in group I were decreased significantly after the treatment (t = 2.611, 2.275, and 2.480 respectively; P<0.05) but had no significant difference in group II after the treatment (t = 1.906, 1.833, and 2.029 respectively; P>0.05). The total effective rate had no significant difference between the two groups (X² = 2.882, P>0.05) but the markedly effective rate was significantly different between the two groups (X² = 5.340, P<0.05).

CONCLUSION: HJT is effective in treating chronic hepatitis B. HJT seems to exert its effect by improving the cellular immune function and decreasing inflammatory cytokines in chronic hepatitis B patients. The function of HJT in protecting liver function in the process of eliminating virus needs to be further studied.

Natural killer cells in hepatitis C virus infection: from innate immunity to adaptive immunity

Natural killer (NK) cells are specialized lymphocytes that provide a first line of defense through their ability to kill pathogen-infected cells and transformed cells. The function of NK cells is regulated by a fine balance of inhibitory and activating signals, which are mediated by a diverse array of cell-surface receptors. We recently found that expression of the inhibitory receptor CD94/NKG2A is up-regulated on NK cells in patients with chronic hepatitis C. HLA-E, a ligand for NKG2A, was expressed in all human hepatoma cell lines tested as well as in nontransformed hepatocytes, but not in K562 cells, a classic NK-sensitive target. NK cells isolated from patients with chronic hepatitis C (HCV-NK) were less capable of killing hepatoma cells and of producing interferon-gamma in response to hepatoma cells than those from healthy donors, whereas there was no significant difference in NK responsiveness toward K562 cells. Of note is the finding that maturation and activation of monocyte-derived dendritic cells were negatively modulated in the presence of HCV-NK and hepatoma cells, which were restored by the addition of anti-NKG2A antibody during the coculture of HCV-NK and hepatoma cells. Research revealed that dendritic cells recognize danger signals from microorganisms by monitoring pathogen-associated molecular patterns via Toll-like receptors. Our findings have shed light on NK receptors as an important interface that transmits danger signals from abnormal cells to immune systems. Aberrant expression of CD94/NKG2A should have negative impact on innate resistance and subsequent adaptive immunity toward HCV-infected or transformed cells in chronic hepatitis C.

Hepatitis C virus and the immune system: a concise review

Hepatitis C Virus (HCV) induces a chronic infection in 50%-80% of infected individuals, which can lead to cirrhosis and hepatocellular carcinoma. The inefficiency of the immune system in eliminating the virus is not well understood as humoral and cellular immune responses are induced. While a persistent infection is generally associated with a weak CD4+ and CD8+ T cell response during the acute phase, there is no good explanation as to why this response is strong enough in 20% of acutely infected people such that they spontaneously resolve the infection. However, the immune system partially controls the viral infection but due to a long-lasting inflammatory milieu, hepatic damage occurs. During the chronic phase of the infection, HCV does not seem to be cytopathic. This aspect is still controversial as the virus was linked to the development of cholestatic syndrome or acute lobular hepatitis after liver transplant in HCV infected patients. The development of new experimental systems such as HCV pseudoparticles, genomic replicon and transfected cell lines have improved our vision of the virus cycle as well as the understanding of the mechanism of persistence. However, a convincing explanation for the chronicity of the infection in the presence of a functional immune response is still missing and is an important area of research to understand HCV immune pathogenesis. Future research should dissect mechanisms that lead to quantitatively or qualitatively inadequate immune responses, the role of the high variability of the virus, the relevance of host's genetic factors and mechanisms of immunosuppression induced by the virus.

Adaptive immune responses in acute and chronic hepatitis C virus infection

The hepatitis C virus (HCV) persists in the majority of infected individuals and is a significant cause of human illness and death globally. Recent studies have yielded important insights into immunity to HCV, in particular revealing the central role of T cells in viral control and clearance. Other key features of adaptive immune responses remain obscure, including mechanisms by which T cells control HCV replication, the role of antibodies in conferring protection and how cellular and humoral immunity are subverted in persistent infection.

Immunology of hepatitis B virus and hepatitis C virus infection

More than 500 million people worldwide are persistently infected with the hepatitis B virus (HBV) and/or hepatitis C virus (HCV) and are at risk of developing chronic liver disease, cirrhosis and hepatocellular carcinoma. Despite many common features in the pathogenesis of HBV- and HCV-related liver disease, these viruses markedly differ in their virological properties and in their immune escape and survival strategies. This review assesses recent advances in our understanding of viral hepatitis, contrasts mechanisms of virus-host interaction in acute hepatitis B and hepatitis C, and outlines areas for future studies.