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

Abstract

NK cells are potent activators of dendritic cells (DCs), but it remains obscure how third-party cells affect the ability of NK cells to modulate DC functions. We show here that NK cells derived from healthy donors (N-NK), when cocultured with human liver epithelial cells, induced maturation as well as activation of DCs, such as increased migratory capacity as well as T cell stimulatory activity. In contrast, NK cells from chronic hepatitis C virus-infected donors (HCV-NK) were not capable of activating DCs under the same conditions. In comparison to N-NK, HCV-NK showed higher expression of CD94/NKG2A and produced IL-10 and TGFβ when cultured with hepatic cells, most of which express HLA-E, a ligand for CD94/NKG2A. Blockade of NKG2A restored the ability of HCV-NK to activate DCs, which appeared to result from the reduced NK cell production of IL-10 and TGFβ. The blockade also endowed HCV-NK with an ability to drive DCs to generate Th1-polarized CD4+ T cells. These findings show that NK cell modulation of DCs is regulated by third-party cells through NK receptor and its ligand interaction. Aberrant expression of NK receptors may have an impact on the magnitude and direction of DC activation of T cells under pathological conditions, such as chronic viral infection.

Increased natural cytotoxicity receptor expression and relevant IL‐10 production in NK cells from chronically infected viremic HCV patients

“…The present finding of increased proportions of CD56 bright NK cells in HCV-infected patients is in agreement with the increased proportion of NKG2A-expressing NKp30 + NK cells. However, the fraction of NKG2A + NKp46 + NK cells in HCV patients (38%) by far exceeded the median expression of CD56 bright NK cells (16%), suggesting that during HCV infection functional inhibition of NK cell function is also present in CD56 dim NK cells.In this regard, the decreased lysis of HepG2 targets compared to FO1 melanoma by NK cells from HCV patients was associated with NKG2A/CD94 expression on these cells and is consistent with previous findings showing that NKG2A/CD94 is involved in the negative regulation of NK cells from HCV-infected patients [35]. Interestingly, skewing of NKG2A/NKG2C expression on NK cells with a decrease in NKG2A + cells and increased proportions of NKG2C + cells has been so far demonstrated during chronic HIV infection at advanced stages of disease [27] and during latent CMV infection [46].…”

“…2D). The reduced cytotoxic activity against HepG2 cells observed with fresh NK cells from HCV patients was consistent with previous work showing impairment of the lysis of hepatocellular carcinoma by NK cells; this has been shown to reflect protection from NK-mediated lysis by their expression of increased surface densities of HLA-E molecules recognized by the CD94/NKG2A inhibitory receptors [35,41]. To address this point, additional experiments with an NKG2A + NCR +-KIR -CD56 + NK cell clone derived from one of the HCV-infected patients were performed.…”

“…This point could not be addressed by the design of the present experiments. It remains to be clarified whether the simultaneous presence of decreased NKG2D ligands on DC and conserved/ increased NKp30-NKp30 ligand interaction could lead to unchanged iDC lysis and NK cell activation.The finding of conserved IFN-c production and the "de novo" appearance of IL-10 production upon triggering with a target cell line that is efficiently killed by NK cells from HCV-infected patients agrees with previous observations of increased IL-10 production during HCV infection [35,36]. Increased IL-10 production during chronic persistent HCV infection has been proposed as one of the mechanisms contributing to inefficient virusspecific CD4 + T cell responses [47,48].…”

“…Additional suggestion of the involvement of innate immune mechanism(s) in the establishment of chronic HCV infection derive from the description of NK cell dysfunction (inhibition) following CD16-mediated triggering when CD81 molecules on NK cells are bound to HCV E2 protein [33]. In addition, reduced NK cell triggering mediated by reduced expression of NKG2D ligands (MIC-A and MIC-B) on mature DC (mDC) [34] as well as increased NK cell inhibition through increased CD94/NKG2A expression and TGF-b and IL-10 production [35,36,37] have been suggested to occur during HCV infection.Given the findings of relevant perturbations of NCR and of their involvement in the immune responses against chronic persistent infections including HIV and Mycobacterium tuberculosis [21][22][23][24][25][26][27][28] as well as the possible posttranscriptional regulation of NCR in the presence of increasing concentrations of TGF-b [38], we tried to determine whether HCV-infected patients show relevant modifications of triggering receptor expression and of NK cell functional derangement during the chronic phase of HCV infection. We report here on the analysis of freshly separated peripheral blood NK cells from HCV-infected patients, showing modified patterns of NCR expression and cytokine production.…”

Peripheral virus-specific T-cell interleukin-10 responses develop early in acute hepatitis C infection and become dominant in chronic hepatitis

“…IL-10 is produced by many cell types including dendritic cells (28,29), macrophages, monocytes, NK (30,31) and NKT-cells (32) with pleiotropic effects. For example, IL-10 can downregulate antigen processing by transporter-associated with antigen processing, MHC expression and IL-12 production by antigen-presenting cells (APC) (9,10), resulting in impaired T-cell proliferation, effector function and memory (33).…”