Echinococcus multilocularis induces surface high expression of inhibitory killer immunoglobulin-like receptor on natural killer cells.

Alveolar echinococcosis (AE) is a malignant and fatal parasitic disease caused by the larvae of Echinococcus multilocularis (E. multilocularis), which inhibits the activity and proliferation of natural killer (NK) cells. In this study, the functional alteration of hepatic NK cells and their related molecules were studied. The AE-infected patient's tissue was fixed with formalin, embedded in paraffin, and stained with Masson's trichrome or hematoxylin and eosin (H&E). Single cells from AE-infected patient or E. multilocularis-infected mice were blocked with Fc-receptor (FcR), and stained with monoclonal antibodies, including CD16, CD56, CD3, KIR2DL1, granzyme B, perforin, Interferon gamma (IFN-γ), and tumor necrosis factor-α (TNFα) or isotype control, to measure molecules and cytokines of NK cells and analyzed by flow cytometry. The Sirius red staining was used to quantitate hepatic fibrosis by calculating quantitative collagen deposition. AE can adjust both the number of hepatic CD56+ NK cells and its KIR2DL1 expression processes. Moreover, the overexpression of KIR2DL1 in NK cells could downregulate the functioning of immune cells in the liver area close to parasitic lesions. The number and dysfunction of NK cells in E. multilocularis infection could be related to the molecule dynamics of cell surface inhibitory receptor Ly49A, leading to hepatic damage and progression of fibrosis. This study illustrated significant increase in hepatic fibrogenesis and apparent upregulation of hepatic CD56+ NK cell population and its KIR2DL1 expression in AE-infected patients. This opposite variation might be related to the impaired NK cells functioning, such as granzyme B, IFN-γ, and TNF-α secretion. In addition, the cell surface inhibitory receptor Ly49A was related to the intracellular cytokine secretion functions of NK cells.

Nanoscale Colocalization of NK Cell Activating and Inhibitory Receptors Controls Signal Integration.

Natural killer (NK) cell responses depend on the balance of signals from inhibitory and activating receptors. However, how the integration of antagonistic signals occurs upon NK cell-target cell interaction is not fully understood. Here we provide evidence that NK cell inhibition via the inhibitory receptor Ly49A is dependent on its relative colocalization at the nanometer scale with the activating receptor NKG2D upon immune synapse (IS) formation. NKG2D and Ly49A signal integration and colocalization were studied using NKG2D-GFP and Ly49A-RFP-expressing primary NK cells, forming ISs with NIH3T3 target cells, with or without the expression of single-chain trimer (SCT) H2-Dd and an extended form of SCT H2-Dd-CD4 MHC-I molecules. Nanoscale colocalization was assessed by Förster resonance energy transfer between NKG2D-GFP and Ly49A-RFP and measured for each synapse. In the presence of their respective cognate ligands, NKG2D and Ly49A colocalize at the nanometer scale, leading to NK cell inhibition. However, increasing the size of the Ly49A ligand reduced the nanoscale colocalization with NKG2D, consequently impairing Ly49A-mediated inhibition. Thus, our data shows that NK cell signal integration is critically dependent on the dimensions of NK cell ligand-receptor pairs by affecting their relative nanometer-scale colocalization at the IS. Our results together suggest that the balance of NK cell signals and NK cell responses is determined by the relative nanoscale colocalization of activating and inhibitory receptors in the immune synapse.

IL-2 mediates NK cell proliferation but not hyperactivity.

Natural killer cells play a major role in innate immunity against tumor and virus-infected cells. NK cells express activating and inhibitory receptors to regulate their function. It has been established that modulation in the NK cell receptor profile results in altered function of NK cell against target cells. Here, we study the effect of IL-2 stimulation on NK cell inhibitory receptors Ly49A, Ly49C, and activating receptor Ly49D in C57BL/6 mice. It was observed that there was significant increase in expression of Ly49A but no change in expression of Ly49C and Ly49D on IL-2 stimulation. We further noticed that although IL-2 stimulation increased the NK cell population and expression of activation marker NK1.1 but IL-2 stimulation does not cause hyper-responsiveness in NK cells, as there was no increase in MIP-1α and IFN-γ production in IL-2 stimulated NK cells as compared to unstimulated controls. These findings provide a framework to understand the effect of IL-2 stimulation on cognate and non-cognate receptor ligand interactions and suggest stratagies for immunotherapies in conjunction with IL-2 combinatorial therapies.