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A Moretta

Publications and source records attributed to A Moretta.

At least 55 records · Page 3Linked to original sources
PubMed2000

Triggering receptors involved in natural killer cell-mediated cytotoxicity against choriocarcinoma cell lines.

The lack of classical HLA-class I molecules on trophoblast is necessary to prevent allorecognition by maternal CTL, but may induce activation of NK cells. A protective role against NK cells equipped of suitable inhibitory receptors has been proposed for nonclassical HLA-class I molecules including HLA-E and HLA-G. In the present study we show that the NK-mediated killing of two choriocarcinoma cell lines, JAR and JEG3, is induced upon engagement of natural cytotoxicity receptors (NCR) with their specific ligands. In particular, we show that NKp44, a triggering receptor expressed at the NK cell surface only after in vitro culture in the presence of IL-2, plays a central role in triggering NK cytotoxicity against trophoblast cells. Also NKp46 appear to contribute to this function by cooperating with NKp44. On the other hand, other triggering receptors such as NKp30, 2B4, and NKG2D are not involved in killing of choriocarcinoma. Our findings suggest that resistance of trophoblast to NK-mediated cytotoxicity is the result of insufficient activating interactions between the various triggering NK receptors and their target cell ligands. On the other hand, the interaction of nonclassical HLA class I molecules with inhibitory NK receptors appears to play only a marginal role in regulating the susceptibility of choriocarcinoma to NK mediated cytotoxicity.

Antibodies, Monoclonal↗
PubMed2000

The human natural cytotoxicity receptors (NCR) that induce HLA class I-independent NK cell triggering.

The cytolytic activity mediated by human natural killer (NK) cells is the result of a balance between signals delivered by inhibitory and activating receptors. The inhibitory receptors are represented by different families of HLA-specific receptors characterized by immunoreceptor tyrosine-based inhibiting motif(ITIM) sequences in their cytoplasmic portion. The function and the specificity of the inhibitory receptors imply the existence of triggering receptors specific for non-HLA ligands that are responsible for the induction of the cytolytic activity against HLA class I-deficient target cells. These receptors have remained elusive until recently when three distinct NK-specific molecules, termed natural cytotoxicity receptors (NCR), were identified and cloned. The different members of this novel family of receptors play a complementary role in the recognition and lysis of target cells. The NCR family is composed by a heterogeneous group of molecules belonging to the Ig superfamily that associate to different immunoreceptor tyrosine-based activating motif (ITAM)-containing signal transducing polypeptides.

Cytotoxicity, Immunologic↗
PubMed1999

Engagement of p75/AIRM1 or CD33 inhibits the proliferation of normal or leukemic myeloid cells.

P75/AIRM1 is a recently identified surface molecule that belongs to the sialoadhesin family and displays homology with the myeloid cell antigen CD33. In lymphoid cells, p75/AIRM1 is confined to natural killer cells and mediates inhibition of their cytolytic activity. In this study, we show that p75/AIRM1 is also expressed by cells of the myelomonocytic cell lineage, in which it appears at a later stage as compared with CD33. In vitro proliferation and differentiation of cord blood-derived CD34(+) cells (induced by stem cell factor and granulocyte-macrophage colony-stimulating factor) were consistently inhibited by the addition of anti-p75/AIRM1 mAb. Engagement of CD33 led to inhibition in some experiments. A sharp decrease of cell proliferation/survival was detected in all three p75/AIRM1+ chronic myeloid leukemias analyzed when cultured in the presence of either anti-p75/AIRM1 or anti-CD33 mAbs. Thus, the present study suggests that p75/AIRM1 and CD33 may play a regulatory role in normal myelopoiesis and may be viewed as suitable target molecules to counteract the proliferation/survival of chronic myeloid leukemias.

Antibodies, Monoclonal↗
PubMed1999

Identification and molecular characterization of NKp30, a novel triggering receptor involved in natural cytotoxicity mediated by human natural killer cells.

Two major receptors involved in human natural cytotoxicity, NKp46 and NKp44, have recently been identified. However, experimental evidence suggested the existence of additional such receptor(s). In this study, by the generation of monoclonal antibodies (mAbs), we identified NKp30, a novel 30-kD triggering receptor selectively expressed by all resting and activated human natural killer (NK) cells. Although mAb-mediated cross-linking of NKp30 induces strong NK cell activation, mAb-mediated masking inhibits the NK cytotoxicity against normal or tumor target cells. NKp30 cooperates with NKp46 and/or NKp44 in the induction of NK-mediated cytotoxicity against the majority of target cells, whereas it represents the major triggering receptor in the killing of certain tumors. This novel receptor is associated with CD3zeta chains that become tyrosine phosphorylated upon sodium pervanadate treatment of NK cells. Molecular cloning of NKp30 cDNA revealed a member of the immunoglobulin superfamily, characterized by a single V-type domain and a charged residue in the transmembrane portion. Moreover, we show that NKp30 is encoded by the previously identified 1C7 gene, for which the function and the cellular distribution of the putative product were not identified in previous studies.

Animals↗
PubMed1999

Identification and molecular cloning of p75/AIRM1, a novel member of the sialoadhesin family that functions as an inhibitory receptor in human natural killer cells.

In this study, by the generation of a specific monoclonal antibody, we identified p75/AIRM1 (for adhesion inhibitory receptor molecule 1), a novel inhibitory receptor that is mostly confined to human natural killer cells. p75/AIRM1 is a 75-kD glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates to src homology 2 domain-bearing protein tyrosine phosphatase (SHP)-1. The p75/AIRM1 gene is located on human chromosome 19 and encodes a novel member of the sialoadhesin family characterized by three immunoglobulin-like extracellular domains (one NH(2)-terminal V-type and two C2-type) and a classical immunoreceptor tyrosine-based inhibitory motif (ITIM) in the cytoplasmic portion. The highest amino acid sequence similarity has been found with the myeloid-specific CD33 molecule and the placental CD33L1 protein. Similar to other sialoadhesin molecules, p75/AIRM1 appears to mediate sialic acid-dependent ligand recognition.

Amino Acid Sequence↗
PubMed1999

Inhibitory receptors sensing HLA-G1 molecules in pregnancy: decidua-associated natural killer cells express LIR-1 and CD94/NKG2A and acquire p49, an HLA-G1-specific receptor.

Trophoblastic cells lack classical HLA class I and class II molecules but express HLA-G1. Although this may prevent allorecognition by maternal T cells, it renders trophoblastic cells potentially susceptible to lysis by natural killer (NK) cells. As shown here, only a fraction of peripheral-blood NK cells in pregnant women express the HLA-G1-specific CD94/NKG2A and/or LIR-1 receptors. However, all NK cells isolated from maternal decidua during the first trimester expressed either one or both of these receptors. Perhaps more importantly, a fraction of cells expressed p49, an HLA-G1-specific inhibitory receptor, undetectable in peripheral-blood NK cells. p49 was expressed on virtually all NK cells isolated from placenta at term. Functional analyses revealed that the HLA class I-negative 221 lymphoblastoid cell line transfected with HLA-G1 was only partially protected from lysis by peripheral-blood NK cells isolated from pregnant women, whereas it was fully protected from decidual NK cells. As indicated by the addition of specific antibodies to cytolytic tests, all the above receptors contributed to HLA-G1 recognition by decidual NK cells, although p49 would appear to play a predominant role.

Animals↗
PubMed1999

NKp44, a triggering receptor involved in tumor cell lysis by activated human natural killer cells, is a novel member of the immunoglobulin superfamily.

Surface receptors involved in natural killer (NK) cell triggering during the process of tumor cell lysis have recently been identified. Of these receptors, NKp44 is selectively expressed by IL-2- activated NK cells and may contribute to the increased efficiency of activated NK cells to mediate tumor cell lysis. Here we describe the molecular cloning of NKp44. Analysis of the cloned cDNA indicated that NKp44 is a novel transmembrane glycoprotein belonging to the Immunoglobulin superfamily characterized by a single extracellular V-type domain. The charged amino acid lysine in the transmembrane region may be involved in the association of NKp44 with the signal transducing molecule killer activating receptor-associated polypeptide (KARAP)/DAP12. These molecules were found to be crucial for the surface expression of NKp44. In agreement with data of NKp44 surface expression, the NKp44 transcripts were strictly confined to activated NK cells and to a minor subset of TCR-gamma/delta+ T lymphocytes. Unlike genes coding for other receptors involved in NK cell triggering or inhibition, the NKp44 gene is on human chromosome 6.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Functional and structural analysis of cis-proline mutants of Escherichia coli aspartate aminotransferase.

To elucidate the role of the two conserved cis-proline residues of aspartate aminotransferase (AspAT), one double and two single mutants of the enzyme from Escherichia coli (EcAspAT) were prepared: P138A, P195A and P138A/P195A in which the two prolines were replaced by alanine. The crystal structures of P195A and P138A/P195A have been determined at 2.3-2.1 A resolution. The wild-type geometry, including the cis conformation of the 194-195 peptide bond is retained upon substitution of proline 195 by alanine, whereas the trans conformation is adopted at the 137-138 peptide bond. Quite surprisingly, the replacement of each of the two prolines by alanine does not significantly affect either the activity or the stability of the protein. All the three mutants follow the same pathway as the wild type for unfolding equilibrium induced by guanidine hydrochloride [Herold, M., and Kirschner, K. (1990) Biochemistry 29, 1907-1913]. The kinetics of renaturation of P195A, where the alanine retains the wild-type cis conformation, is faster than wild type, whereas renaturation of P138A, which adopts the trans conformation, is slower. We conclude that cis-prolines seem to have been retained throughout the evolution of aspartate aminotransferase to possibly play a subtle role in directing the traffic of intermediates toward the unique structure of the native state, rather than to respond to the needs for a specific catalytic or functional role.

Alanine↗
PubMed1999

The murine homologue of the human NKp46, a triggering receptor involved in the induction of natural cytotoxicity.

The NKp46 molecule has been proposed to play the role of triggering receptor in the natural cytotoxicity mediated by human NK cells. In this study we have identified the gene encoding the murine NKp46 homologue that we termed MAR-1. The MAR-1 gene is localized on chromosome 7 that is synthenic to the human chromosome 19 where the NKp46 gene is located. MAR-1 encodes a type I transmembrane glycoprotein belonging to the immunoglobulin (Ig) superfamily that, like human NKp46, is characterized by two C2-type Ig-like domains, a transmembrane portion containing a positively charged residue and a cytoplasmic tail lacking the immunoreceptor tyrosine-based activation motif (ITAM). The MAR-1 protein is expressed on the surface of cell transfectants and displays a molecular mass of approximately 46 kDa similar to that of its human counterpart. Semiquantitative RT-PCR analysis showed that MAR-1, similar to the human NKp46, is selectively expressed by NK cells. The MAR-1 protein displays 58 % identity with the human NKp46 receptor. This high homology together with the presence of a charged amino acid (Arg) in the transmembrane portion suggest that MAR-1 may associate at the cell membrane into a multimeric complex with ITAM containing polypeptides.

Amino Acid Sequence↗
PubMed1999

Inefficient protection of human TAP-deficient fibroblasts from autologous NK cell-mediated lysis by cytokines inducing HLA class I expression.

We studied HLA class I expression and susceptibility to lysis of activated autologous NK cells in normal and TAP-deficient fibroblasts. These cells were cultured in the presence or absence of cytokines known to increase the surface expression of HLA class I molecules. All the cytokines tested (IFN-alpha, IFN-gamma, TNF-alpha and IFN-gamma + TNF-alpha) increased the expression of HLA class I molecules on fibroblasts after 48-h culture, but on TAP-deficient cells this expression remained very low as compared to that of normal cells. In the presence of IFN-alpha, IFN-gamma or IFN-gamma + TNF-alpha, normal target cells became resistant to lysis by autologous NK cells, whereas this effect was much less pronounced in the case of TAP-deficient fibroblasts. Addition of an anti-HLA class I mAb to fibroblasts treated with cytokines increased lysis of normal but not of TAP-deficient cells. These results suggest that activated TAP-deficient NK cells are strongly cytotoxic to normal autologous cells and that these cells cannot be efficiently protected by cytokines inducing HLA class I expression. Thus, in human TAP deficiency, activated NK cells may contribute to the progressive lung degradation which characterizes the clinical course of these patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

NKp46 is the major triggering receptor involved in the natural cytotoxicity of fresh or cultured human NK cells. Correlation between surface density of NKp46 and natural cytotoxicity against autologous, allogeneic or xenogeneic target cells.

NKp46 is a novel triggering receptor expressed by all human NK cells that is involved in natural cytotoxicity. In this study we show that the surface density of NKp46 may vary in different NK cells and that a precise correlation exists between the NKp46 phenotype of NK clones and their natural cytotoxicity against HLA-class I-unprotected allogeneic or xenogeneic cells. Thus, NKp46bright clones efficiently lysed human and murine tumor cells while NKp46dull clones were poorly cytolytic against both types of target cells. We also show that the NKp46 phenotype of NK clones correlates with their ability to lyse HLA-class I-unprotected autologous cells. Finally, NKp46 was found to be deeply involved in the natural cytotoxicity mediated by freshly derived NK cells. This was indicated both by the inhibition of cytolysis after monoclonal antibody-mediated masking of NKp46 and by the correlation existing between the natural cytotoxicity of fresh NK cells derived from different donors and their NKp46 phenotype. In conclusion, these studies strongly support the concept that NKp46 plays a central role in the physiological triggering of NK cells and, as a consequence (in concert with killer inhibitory receptors), in the NK-mediated clearance of abnormal cells expressing inadequate amounts of HLA-class I molecules.

Cells, Cultured↗
PubMed1999

Molecular and functional characterization of IRp60, a member of the immunoglobulin superfamily that functions as an inhibitory receptor in human NK cells.

In this study we describe the functional and molecular characterization of IRp60 (inhibitory receptor protein 60), an inhibitory receptor expressed on all human NK cells. The IRp60 molecule has been identified by the generation of three novel monoclonal antibodies (mAb). Cross-linking of IRp60 by specific mAb strongly inhibits the spontaneous cytotoxicity of NK cells as well as the NK-mediated cytolytic activity induced via different non-HLA-specific or HLA-specific activating receptors. IRp60 is a 60-kDa glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates with the SH2-containing phosphatases SHP-1 and SHP-2. The IRp60 gene is located on human chromosome 17 and encodes a molecule belonging to the immunoglobulin (Ig) superfamily characterized by a single V-type Ig-like domain in the extracellular portion. The cytoplasmic tail contains three classical immunoreceptor tyrosine-based inhibitory motifs. Southern blot analysis revealed cross-hybridization with monkey and mouse genomic DNA, thus suggesting that IRp60 may be conserved among different species. Moreover, based on the use of different anti-IRp60 mAb, we could identify two IRp60 allelic variants. Since IRp60 is also expressed by other cell types, including T cell subsets, monocytes and granulocytes, it may play a more general role in the negative regulation of different leukocyte populations.

Amino Acid Sequence↗
PubMed1999

Natural killer cell-mediated recognition of human trophoblast.

Large numbers of natural killer cells are present within the maternal decidua close to the extravillous trophoblast cells. Most of these natural killer cells express high levels of inhibitory NK receptors (KIR) specific for HLA class I molecules. Since trophoblast cells only express HLA-C and HLA-G, the KIR expressed by decidual NK cells can only recognize these HLA class I molecules in order to avoid NK-mediated rejection of fetal tissues. We show that HLA-C recognition by decidual NK cells can be mediated by p58, LIR-1 and (indirectly) by CD94/NKG2A receptors. On the other hand, HLA-G recognition is not only mediated by LIR-1 and (indirectly) by CD94/NKG2A but also by a newly identified receptor termed p49. The p49 receptor, unlike the other KIR, appears to be selectively expressed by decidual NK cells.

Alleles↗