Paola Costa

The impaired NK cell cytolytic function in viremic HIV‐1 infection is associated with a reduced surface expression of natural cytotoxicity receptors (NKp46, NKp30 and NKp44)

Signals leading to NK cell triggering are primarily mediated by natural cytotoxicity receptors (NCR) upon binding to as‐yet‐undefined cell surface ligand(s) on normal hematopoietic cells, pathogen‐infected cells or tumor cells. In this study we tried to determine whether the decreased NK cell cytolytic function that is observed in HIV‐1‐infected patients may be related to a decreased expression of NCR. In HIV‐1‐infected patients, freshly drawn, purified NK cells expressed significantly decreased surface densities of NKp46 and NKp30 NCR. The low surface density of NKp46, NKp30 and NKp44 was also confirmed in in‐vitro‐activated NK cell populations and NK cell clones derived from HIV‐1 patients compared with uninfected donors. This defective NCR expression in HIV‐1 patients was associated with a parallel decrease of NCR‐mediated killing of different tumor target cells. Thus, the present study indicates that the defective expression of NCR represents at least one of the possible mechanisms leading to the impaired NK cell function in HIV‐1 infection and it can contribute to explain the relatively high frequency of opportunistic tumors reported in cohorts of untreated patients before the occurrence of profound immunosuppression (<200 CD4+ cells/mm3).

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

Hepatitis C virus (HCV) readily establishes high‐level lifelong persistent infection in the majority of immunocompetent adults with failure of HCV‐specific CD8+ CTL to clear viral replication. Virus‐induced conditioning of innate immune responses is a possible mechanism that may contribute to the impairment of virus‐specific CD8+ CTL responses. Here, we analyzed whether triggering of NK cell receptor expression and function is affected during chronic viremic HCV infection. Flow cytometric analysis of purified resting peripheral NK cells showed no evidence of NK cell activation, while analysis of natural cytotoxicity receptors (NCR) showed that NK cells from HCV‐infected patients had selective increased expression of NKp30 and NKp46. NK cells had corresponding conserved cytotoxic activity against all targets with the exception of HepG2 hepatoma cells. Freshly separated NK cells from HCV patients showed significant production of IL‐10 and normal concentrations of IFN‐γ upon cell‐mediated triggering. Thus, increased expression of NKp30 during HCV infection with increased IL‐10 production could contribute, once NK cells localize in the liver, to a NK‐DC crosstalk leading to skewing of subsequent adaptive immune responses and lack of virus control.

Significant NK cell activation associated with decreased cytolytic function in peripheral blood of HIV-1-infected patients

One of the hallmarks of HIV‐1 infection is represented by the finding of massive T cell activation in peripheral blood lymphocytes of infected patients. An impairment of NK cell function during HIV‐1 infection is also detected, and is associated with decreased expression of natural cytotoxicity receptors (NCR). In this study we tried to determine whether also NK cells are affected by relevant activation and whether this could be associated with decreased NK cell function. In 18 viremic HIV‐1‐infected patients, freshly drawn purified peripheral NK cells displayed significant levels of activation with an incomplete pattern (HLA‐DR+CD69+CD25–NKp44–). Activated (HLA‐DR+CD69+) peripheral NK cells expressed an NCRdull phenotype as determined by cytofluorometric analysis in all the patients, and did not derive from a homogeneous/oligoclonal expansion in vivo as analyzed by expression of HLA‐specific inhibitory NK cell receptors. As determined by cytotoxicity assays, activated NK cells showed a decreased cytolytic function in HIV‐1‐infected patients. Thus, the decrease in NK cell function observed during HIV‐1 infection is associated not only with decreased NCR expression, but also with significant and incomplete NK cell activation in vivo. These results suggest a consistent continuous involvement of the innate immune response in the failure to control viral replication.

Activating NK cell receptor expression/function (NKp30, NKp46, DNAM‐1) during chronic viraemic HCV infection is associated with the outcome of combined treatment

Specific NK cell killer inhibitory receptor (KIR):HLA haplotype combinations have been associated with successful clearance of acute and chronic HCV infection. Whether an imbalance of activating NK cell receptors also contributes to the outcome of treatment of chronic HCV infection, however, is not known. We studied peripheral NK cell phenotype and function in 28 chronically viraemic HCV genotype I treatment‐naïve patients who underwent treatment with pegylated IFN‐α and ribavirin. At baseline, chronically infected patients with sustained virological response (SVR) had reduced CD56brightCD16+/− cell populations, increased CD56dullCD16+ NK cell proportions, and lower expression of NKp30, DNAM‐1, and CD85j. Similarly, reduced NK cell IFN‐γ production but increased degranulation was observed among nonresponding (NR) patients. After treatment, CD56brightCD16+/− NK cell numbers increased in both SVR and NR patients, with a parallel significant increase in activating NKp30 molecule densities in SVR patients only. In vitro experiments using purified NK cells in the presence of rIL‐2 and IFN‐α confirmed upregulation of NKp30 and also of NKp46 and DNAM‐1 in patients with subsequent SVR. Thus, differences in patient NK cell receptor expression and modulation during chronic HCV‐1 infection are associated with subsequent outcome of standard treatment. Individual activating receptor expression/function integrates with KIR:HLA genotype carriage to determine the clearance of HCV infection upon treatment.

IL-12-induced up-regulation of NKRP1A expression in human NK cells and consequent NKRP1A-mediated down-regulation of NK cell activation.

IL‐12, in contrast to IL‐2, strongly up‐regulated the expression of the NKRP1A lectin molecule on human NK cells. This effect appeared to be specific for NKRP1A as the expression of other functional NK cell surface molecules such as CD16 and different killer inhibitory receptors (KIR) including CD158a and CD158b, p70 and p140 were not affected by culture in IL‐12. In addition, we found that polyclonal or clonal NK cell populations derived in the presence of IL‐2 displayed an increased expression of NKRP1A after culture in IL‐12. The IL‐12‐induced NKRP1A expression was time and dose dependent, reaching a maximum by 7 days of culture in the presence of 2 ng/ml IL‐12 and it was inhibited by the addition of anti‐IL‐12 monoclonal antibody. The IL‐12‐dependent NKRP1A up‐regulation was abrogated by the incubation of NK cells with actinomycin D, thus suggesting that IL‐12 induces de novo transcription of NKRP1A mRNA. Functional analysis revealed that the engagement of the NKRP1A molecule in IL‐12‐ but not in IL‐2‐cultured NK cells leads to a strong inhibition of the cytolytic activity induced by cross‐linking of CD16 or p46, a recently described NK cell‐specific triggering surface molecule. Our findings suggest that IL‐12 up‐regulates the expression of NKRP1A which, in turn, can regulate NK cell activation induced via different triggering pathways. This would imply that NKRP1A‐mediated functions may be regulatd by the cytokine microenvironment that NK cells may encounter at inflammatory sites.

Differential disappearance of inhibitory natural killer cell receptors during HAART and possible impairment of HIV-1-specific CD8 cytotoxic T lymphocytes.

BackgroundHighly active antiretroviral therapy (HAART) is associated with a decrease in viral replication to undetectable levels and with an increase in CD4 T lymphocytes. Residual HIV-1 replication occurs together with incomplete recovery of cytotoxic CD8 T lymphocyte (CTL) numbers and function. We sought to determine whether expression of HLA class I-specific inhibitory natural killer receptors (iNKR) on the CTL of patients who had been treated successfully with HAART for 24 months could be involved, at least in part, in residual CTL functional inhibition. MethodsTwo-colour cytofluorometry was used to analyse the expression of six different iNKR including p58.1, p58.2, p70, p140, CD94/NKG2A and LIR1/ILT2 on the CD3, CD8 lymphocytes of eight patients with successful long-term suppression of viral replication before and after 3, 6 and 24 months of HAART. Healthy subjects were analysed as controls. HIV-1-specific cytotoxic activity was determined after 24 months of HAART in the presence and absence of iNKR-masking. ResultsNo significant reduction of iNKR expression on CD8 T cells was observed by 6 months. Expression of p70 and p140 was inversely correlated with the increasing CD4 numbers. After 24 months CD8 T-lymphocytes expressing p58.1, p58.2, p70, p140 and CD94/NKG2A returned to levels indistinguishable from those of the healthy controls. A significantly increased proportion of CD8 CTL still expressed LIR1/ILT2, a receptor with broad HLA-class I specificity. Functional analysis of freshly separated cells revealed that the disruption of the interaction between LIR1/ILT2 and HLA-class I could partly restore HIV-1-specific lysis. ConclusionsA decrease in CD3CD8iNKR cells is observed beyond 6 months of HAART. In some patients functional impairment due to LIR1/ILT2 expression may persist even after 24 months of successful HAART.

Molecular and Functional Characterization of NKG2D, NKp80, and NKG2C Triggering NK Cell Receptors in Rhesus and Cynomolgus Macaques: Monitoring of NK Cell Function during Simian HIV Infection

An involvement of innate immunity and of NK cells during the priming of adaptive immune responses has been recently suggested in normal and disease conditions such as HIV infection and acute myelogenous leukemia. The analysis of NK cell-triggering receptor expression has been so far restricted to only NKp46 and NKp30 in Macaca fascicularis. In this study, we extended the molecular and functional characterization to the various NK cell-triggering receptors using PBMC and to the in vitro-derived NK cell populations by cytofluorometry and by cytolytic activity assays. In addition, RT-PCR strategy, cDNA cloning/sequencing, and transient transfections were used to identify and characterize NKp80, NKG2D, CD94/NKG2C, and CD94/NKG2A in M. fascicularis and Macaca mulatta as well as in the signal transducing polypeptide DNAX-activating protein DAP-10. Both M. fascicularis and M. mulatta NK cells express NKp80, NKG2D, and NKG2C molecules, which displayed a high degree of sequence homology with their human counterpart. Analysis of NK cells in simian HIV-infected M. fascicularis revealed reduced surface expression of selected NK cell-triggering receptors associated with a decreased NK cell function only in some animals. Overall surface density of NK cell-triggering receptors on peripheral blood cells and their triggering function on NK cell populations derived in vitro was not decreased compared with uninfected animals. Thus, triggering NK cell receptor monitoring on macaque NK cells is possible and could provide a valuable tool for assessing NK cell function during experimental infections and for exploring possible differences in immune correlates of protection in humans compared with cynomolgus and rhesus macaques undergoing different vaccination strategies.

Functionally relevant decreases in activatory receptor expression on NK cells are associated with pulmonary tuberculosis in vivo and persist after successful treatment.

Correlates for the initiation of Mycobacterium tuberculosis hominis (Mth) replication from latency are needed in order to improve Mth control. In order to analyze if perturbations of peripheral NK cells may be associated with exit from Mth latency, sequential patients with newly diagnosed lung tuberculosis (TB) were studied. Peripheral NK cells were analyzed by cytofluorometry, in vitro culture and functional assays. At the onset of lung TB, imbalances in NK cell subsets were evident. Decreased CD56(bright)CD16(+/-) subsets with significantly compromised NKp30 and NKp46 expression and with specifically decreased gamma-IFN production upon triggering were evident. These features were not completely restored when purified NK cells were cultured in vitro. Culture supplementation with alpha-IFN increased only NKp30 expression in TB and healthy donors. Extensive peripheral NK cell triggering was evident in these patients, as shown by the expression of NK cell activation markers and of the lymph node-homing chemokine receptor CCR7 on CD16(+) CD56(dull) cells. Significant persistence of decreased NKp30 and NKp46 after successful treatment with a standard four-drug regimen was detected after full recovery. NK cell function is deeply affected in patients at the onset of pulmonary TB. The involvement of multiple activatory receptors may provide a relevant contribution to the spread of mycobacteria exiting from latency.

Differential NKp30 inducibility in chimpanzee NK cells and conserved NK cell phenotype and function in long-term HIV-1-infected animals

HIV-1 infection in chimpanzees, the closest human relative, rarely leads to disease progression. NK cells contribute to the shaping of adaptive immune responses in humans and show perturbed phenotype and function during HIV-1 infection. In this study, we provide full phenotypic, molecular, and functional characterization for triggering molecules (NKp46, NKp30 NKp80, and NKG2D) on Pan troglodytes NK cells. We demonstrate that, in this AIDS-resistant species, relevant differences to human NK cells involve NKp80 and particularly NKp30, which is primarily involved in NK-dendritic cell interactions. Resting peripheral chimpanzee NK cells have low or absent NKp30 molecule expression due to posttranscriptional regulation and increase its levels upon in vitro activation. Following long-standing HIV-1 infection, peripheral NK cells in chimpanzees have conserved triggering receptor expression and display moderate phenotypic and functional decreases only once activated and cultured in vitro. These data suggest that one of the keys to successful lentivirus control may reside in part in a different regulation of NK cell-triggering receptor expression.

NKRP1A molecule is involved in transendothelial migration of CD4+ human T lymphocytes

Among human CD4+ T lymphocytes, 5-20% express the C-type lectin molecule NKRP1A. Interestingly, CD4+ NKRP1A+ T lymphocytes express high levels of beta 1 and beta 2 integrins, thus representing a T lymphocyte subset that can possibly adhere and migrate through vascular endothelium. Indeed, resting CD4+ NKRP1A+ lymphocytes, differently from the CD4+ NKRP1A- subset, migrated across endothelial cell monolayers in a Transwell chamber system. This transendothelial migration was strongly reduced after pre-treatment with an anti-NKRP1A monoclonal antibody (mAb). In addition, the NKRP1A negative Jurkatt CD4+ T-cell line that had been stably transfected with NKRP1A cDNA, migrated more rapidly and efficiently than untransfected Jurkatt cells. Finally, mAb-mediated cross-linking of NKRP1A molecule in CD4+ T lymphocytes induced the upregulation of the LFA1 Mg2+ binding site as well as beta 1 and beta 2 integrin chains. Altogether, these findings indicate that NKRP1A molecule is involved in transendothelial migration of resting CD4+ T lymphocytes.