Saar Mizrahi

Endometrial NK Cells Are Special Immature Cells That Await Pregnancy

NK cells populate the human endometrium before pregnancy. Unlike decidual NK cells that populate the decidua during pregnancy, the NK cells present in the human endometrium, before pregnancy, have not been fully characterized. In this study, we provide a detailed analysis of the origin, phenotype, and function of endometrial NK cells (eNK). We show that eNK cells have a unique receptor repertoire. In particular, they are negative for NKp30 and chemokine receptor expression, which distinguishes them from any other NK subset described so far. We further show that eNK cells lack NK-specific functional phenotype and activity such as cytokine secretion and cytotoxicity, before IL-15 stimulation. Following such stimulation, endometrial NK cells acquire phenotype and function that are similar to those of decidual NK cells. We therefore suggest that eNK cells are inactive cells (before IL-15 activation and in relation to the known NK activity) that are present in the endometrium before conception, waiting for pregnancy.

The activating receptor NKp46 is essential for the development of type 1 diabetes.

The mechanism of action of natural killer (NK) cells in type 1 diabetes is still unknown. Here we show that the activating receptor NKp46 recognizes mouse and human ligands on pancreatic beta cells. NK cells appeared in the pancreas when insulitis progressed to type 1 diabetes, and NKp46 engagement by beta cells led to degranulation of NK cells. NKp46-deficient mice had less development of type 1 diabetes induced by injection of a low dose of streptozotocin. Injection of soluble NKp46 proteins into nonobese diabetic mice during the early phase of insulitis and the prediabetic stage prevented the development of type 1 diabetes. Our findings demonstrate that NKp46 is essential for the development of type 1 diabetes and highlight potential new therapeutic modalities for this disease.

Complexes of HLA-G Protein on the Cell Surface Are Important for Leukocyte Ig-Like Receptor-1 Function

The nonclassical class I MHC molecule HLA-G is selectively expressed on extravillous cytotrophoblast cells at the maternal-fetal interface during pregnancy. HLA-G can inhibit the killing mediated by NK cells via interaction with the inhibitory NK cell receptor, leukocyte Ig-like receptor-1 (LIR-1). Comparison of the sequence of the HLA-G molecule to other class I MHC proteins revealed two unique cysteine residues located in positions 42 and 147. Mutating these cysteine residues resulted in a dramatic decrease in LIR-1 Ig binding. Accordingly, the mutated HLA-G transfectants were less effective in the inhibition of NK killing and RBL/LIR-1 induced serotonin release. Immunoprecipitation experiments demonstrated the involvement of the cysteine residues in the formation of HLA-G protein oligomers on the cell surface. The cysteine residue located at position 42 is shown to be critical for the expression of such complexes. These oligomers, unique among the class I MHC proteins, probably bind to LIR-1 with increased avidity, resulting in an enhanced inhibitory function of LIR-1 and an impaired killing function of NK cells.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro

To cite this article: Elishmereni M, Alenius HT, Bradding P, Mizrahi S, Shikotra A, Minai‐Fleminger Y, Mankuta D, Eliashar R, Zabucchi G, Levi‐Schaffer F. Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro. Allergy 2011; 66: 376–385.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro.

To cite this article: Elishmereni M, Alenius HT, Bradding P, Mizrahi S, Shikotra A, Minai‐Fleminger Y, Mankuta D, Eliashar R, Zabucchi G, Levi‐Schaffer F. Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro. Allergy 2011; 66: 376–385.

Siglec-7 is an inhibitory receptor on human mast cells and basophils.

The study was supported by grants from the Swedish Research Council (grant no. K2011-56X-21854-01-06), the Ekhaga Foundation, the Olle Engkvist Foundation, the Cancer and Allergy Association, and the University Hospital of Link€oping, Sweden. Disclosure of potential conflict of interest: J. Mj€osberg has received research support from the Swedish Research Council and the Swedish Cancer Society. The rest of the authors declare that they have no relevant conflicts of interest.

Notch activation enhances IFNγ secretion by human peripheral blood and decidual NK cells

NK cells specialize in killing tumor cells and virally infected cells and also possess non-cytotoxic functions, which include secretion of a variety of cytokines and growth factors. Their activity is mediated by a vast repertoire of inhibitory and activating NK receptors. Recently, it was demonstrated that ligation of the Notch receptor plays a significant role not only in T cell development but also in human T cell and mouse NK cell activation. However, the involvement of Notch triggering in human NK cell activity has not yet been determined. Here we show that Notch1 and Notch2, but not Notch3 and Notch 4, are expressed in human peripheral blood NK cells and in decidual NK cells. We demonstrate that in peripheral blood NK cells only the Notch ligand Delta4 could interact with Notch, whereas in decidual NK cells both Delta1 and Delta4 can interact with Notch. Finally, we show that Notch activation in these cells leads to increased secretion of IFNgamma. We therefore present here a new function of the Notch receptors as enhancers of peripheral blood NK cell and decidual NK cell functions.

Loss of kindlin-3 alters the threshold for NK cell activation in human leukocyte adhesion deficiency-III

Recent evidence suggests that kindlin-3 is a major coactivator, required for most, if not all, integrin activities. Here we studied the function of kindlin-3 in regulating NK cell activation by studying a patient with kindlin-3 deficiency (leukocyte adhesion deficiency-III). We found that kindlin-3 is required for NK cell migration and adhesion under shear force. Surprisingly, we also found that kindlin-3 lowers the threshold for NK cell activation. Loss of kindlin-3 has a pronounced effect on NK cell-mediated cytotoxicity triggered by single activating receptors. In contrast, for activation through multiple receptors, kindlin-3 deficiency is overcome and target cells killed. The realization that NK cell activity is impaired, but not absent in leukocyte adhesion deficiency, may lead to the development of more efficient therapy for this rare disease.

Manipulation of NK cytotoxicity by the IAP family member Livin.

Natural killer (NK) cells are part of the innate immune system, capable of killing tumor and virally infected cells. NK cells induce apoptosis in the target cell by either granule‐ or receptor‐mediated pathways. A set of inhibitory and activation ligands governs NK cell activation. As transformed cells often attempt to evade NK cell killing, up‐regulation of a potential anti‐apoptotic factor should provide a survival advantage. The inhibitor of apoptosis protein (IAP) family can inhibit apoptosis induced by a variety of stimuli. We have previously described a new IAP family member, termed Livin, which has two splice variants (α and β) with differential anti‐apoptotic activities. In this study, we explore the ability of Livin to inhibit NK cell‐induced killing. We demonstrate that Livin β moderately protects against NK cell killing whereas Livin α augments killing. We show that Livin β inhibition in Jurkat cells is apparent upon concomitant activation of an inhibitory signal, suggesting that Livin augments an extrinsic inhibitory signal rather than functioning as an independent inhibitory mechanism. Finally, we demonstrate that detection of both Livin isoforms in melanoma cells correlates with a low killing rate. To date, this is the first evidence that directly demonstrates the ability of IAP to protect against NK cell‐induced apoptosis.

Recognition of Mycoplasma hyorhinis by CD99-Fc molecule

The human CD99 protein is expressed on many cell types and is mostly abundant on lymphocytes and on several tumors. Different functions were attributed to the CD99 receptor, including adhesion, apoptosis and activation. However, until now the only ligand suggested to be recognized by CD99 was CD99 itself. In order to identify possible new CD99 ligands we constructed a CD99 protein fused to human IgG1. Surprisingly, a pronounced specific staining of melanoma cell lines that were infected with mycoplasmas was observed whereas clean cells were not recognized. Staining was specific, asother fusion proteins did not recognize the mycoplasma‐infected cells. Sequencing of the 23s–16s region revealed that the contaminating agent is Mycoplasma hyorhinis. The CD99 interaction with M. hyorhinis was direct since it was blocked by anti‐CD99 monoclonal antibody and by M. hyorhinis. It was also strain‐specific as other mycoplasmas were not recognized. Our results show that CD99 interacts with a novel ligand of M. hyorhinis.