Inhibition of natural killer (NK) cells is mediated by MHC class I receptors including the killer cell Ig-like receptor (KIR). We demonstrate that HLA-C binding peptides can function as altered peptide ligands for KIR and antagonize the inhibition mediated by KIR2DL2/ KIR2DL3. Antagonistic peptides promote clustering of KIR at the interface of effector and target cells, but do not result in inhibition of NK cells. Our data show that, as for T cells, small changes in the peptide content of MHC class I can regulate NK cell activity.killer cell immunoglobulin-like receptors | MHC class I

Background and Aims-NK cells are essential early after infection not only for viral containment but also for timely and efficient induction of adaptive responses. An inhibitory effect of HCV-E2 proteins on NK cells has been reported but the features of NK cell responses in the acute phase of hepatitis C are still largely undefined. Therefore, the aim of this study was to characterize function and phenotype of natural killer cells in the acute phase of infection and compare individuals with chronic and self-limited outcomes.

Chemotherapy that is used to treat human immunodeficiency virus type-1 (HIV-1) infection focuses primarily on targeting virally encoded proteins. However, the combination of a short retroviral life cycle and high mutation rate leads to the selection of drug-resistant HIV-1 variants. One way to address this problem is to inhibit non-essential host cell proteins that are required for viral replication. Here we show that the activity of HIV-1 integrase stimulates an ataxia-telangiectasia-mutated (ATM)-dependent DNA damage response, and that a deficiency of this ATM kinase sensitizes cells to retrovirus-induced cell death. Consistent with these observations, we demonstrate that a novel and specific small molecule inhibitor of ATM kinase activity, KU-55933, is capable of suppressing the replication of both wild-type and drug-resistant HIV-1.

Alpha-glucosidase I inhibitors have been shown to inhibit the replication of a broad range of enveloped viruses by preventing the correct folding of their envelope glycoproteins. This study assesses the potential of 6 O-butanoyl castanospermine (celgosivir) as a treatment for hepatitis C virus (HCV). In the absence of an adequate culture system for HCV, the closely related virus, bovine viral diarrhoea virus (BVDV), was used as a surrogate model. Using both a plaque assay and a cytopathic effect assay, celgosivir (IC50 16 and 47 microM respectively) was shown to be more potent than N-nonyl DNJ (105 and 74 microM), castanospermine (110 and 367 microM) and N-butyl DNJ (> 250 and 550 microM). Of the alpha-glucosidase inhibitors tested, only N-nonyl DNJ showed evidence of toxicity (CC50 > or = 120 microM). Two-way combinations of interferon-alpha, ribavirin and either celgosivir or castanospermine demonstrated that each could enhance the antiviral efficacy of the others, either additively or synergistically. The observation that the number of viral genomes released from BVDV-infected cells was inhibited by either castanospermine or celgosivir in parallel with the number of infectious units was taken as confirmation that these alpha-glucosidase I inhibitors block the production or release of flavivirus particles.

Productive engagement of MHC Class I by inhibitory NK cell receptors depends on the peptide bound by the MHC class I molecule. Peptide:MHC complexes that bind weakly to killer cell immunoglobulin-like receptors (KIR) can antagonize the inhibition mediated by high affinity peptide:MHC complexes and cause NK cell activation. We show that low affinity peptide:MHC complexes stall inhibitory signalling at the step of SHP-1 recruitment and do not go on to form the KIR microclusters induced by high affinity peptide:MHC, which are associated with Vav dephosphorylation and downstream signalling. Furthermore the low affinity peptide:MHC complexes prevented the formation of KIR microclusters by high affinity peptide:MHC. Thus peptide antagonism of NK cells is an active phenomenon of inhibitory synapse disruption.