Pseudorabies Virus US3 Protein Kinase Protects Infected Cells from NK Cell-Mediated Lysis via Increased Binding of the Inhibitory NK Cell Receptor CD300a.

UNLABELLED: Several reports have indicated that natural killer (NK) cells are of particular importance in the innate response against herpesvirus infections. As a consequence, herpesviruses have developed diverse mechanisms for evading NK cells, although few such mechanisms have been identified for the largest herpesvirus subfamily, the alphaherpesviruses. The antiviral activity of NK cells is regulated by a complex array of interactions between activating/inhibitory receptors on the NK cell surface and the corresponding ligands on the surfaces of virus-infected cells. Here we report that the US3 protein kinase of the alphaherpesvirus pseudorabies virus (PRV) displays previously uncharacterized immune evasion properties: it triggers the binding of the inhibitory NK cell receptor CD300a to the surface of the infected cell, thereby providing increased CD300a-mediated protection of infected cells against NK cell-mediated lysis. US3-mediated CD300a binding was found to depend on aminophospholipid ligands of CD300a and on group I p21-activated kinases. These data identify a novel alphaherpesvirus strategy for evading NK cells and demonstrate, for the first time, a role for CD300a in regulating NK cell activity upon contact with virus-infected target cells. IMPORTANCE: Herpesviruses have developed fascinating mechanisms to evade elimination by key elements of the host immune system, contributing to their ability to cause lifelong infections with recurrent reactivation events. Natural killer (NK) cells are central in the innate antiviral response. Here we report that the US3 protein kinase of the alphaherpesvirus pseudorabies virus displays a previously uncharacterized capacity for evasion of NK cells. Expression of US3 protects infected cells from NK cell-mediated lysis via increased binding of the inhibitory NK cell receptor CD300a. We show that this US3-mediated increase in CD300a binding depends on aminophospholipids and on cellular p21-activated kinases (PAKs). The identification of this novel NK cell evasion strategy may contribute to the design of improved herpesvirus vaccines and may also have significance for other PAK- and CD300a-modulating viruses and cancer cells.

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.

X-linked lymphoproliferative disease. 2B4 molecules displaying inhibitory rather than activating function are responsible for the inability of natural killer cells to kill Epstein-Barr virus-infected cells.

2B4 is a surface molecule involved in activation of the natural killer (NK) cell-mediated cytotoxicity. It binds a protein termed Src homology 2 domain-containing protein (SH2D1A) or signaling lymphocyte activation molecule (SLAM)-associated protein (SAP), which in turn has been proposed to function as a regulator of the 2B4-associated signal transduction pathway. In this study, we analyzed patients with X-linked lymphoproliferative disease (XLP), a severe inherited immunodeficiency characterized by critical mutations in the SH2D1A gene and by the inability to control Epstein-Barr virus (EBV) infections. We show that, in these patients, 2B4 not only fails to transduce triggering signals, but also mediates a sharp inhibition of the NK-mediated cytolysis. Other receptors involved in NK cell triggering, including CD16, NKp46, NKp44, and NKp30, displayed a normal functional capability. However, their activating function was inhibited upon engagement of 2B4 molecules. CD48, the natural ligand of 2B4, is highly expressed on the surface of EBV(+) B cell lines. Remarkably, NK cells from XLP patients could not kill EBV(+) B cell lines. This failure was found to be the consequence of inhibitory signals generated by the interaction between 2B4 and CD48, as the antibody-mediated disruption of the 2B4-CD48 interaction restored lysis of EBV(+) target cells lacking human histocompatibility leukocyte antigen (HLA) class I molecules. In the case of autologous or allogeneic (HLA class I(+)) EBV(+) lymphoblastoid cell lines, restoration of lysis was achieved only by the simultaneous disruption of 2B4-CD48 and NK receptor-HLA class I interactions. Molecular analysis revealed that 2B4 molecules isolated from either XLP or normal NK cells were identical. As expected, in XLP-NK cells, 2B4 did not associate with SH2D1A, whereas similar to 2B4 molecules isolated from normal NK cells, it did associate with Src homology 2 domain-containing phosphatase 1.

NTB-A [correction of GNTB-A], a novel SH2D1A-associated surface molecule contributing to the inability of natural killer cells to kill Epstein-Barr virus-infected B cells in X-linked lymphoproliferative disease.

In humans, natural killer (NK) cell function is regulated by a series of receptors and coreceptors with either triggering or inhibitory activity. Here we describe a novel 60-kD glycoprotein, termed NTB-A, that is expressed by all human NK, T, and B lymphocytes. Monoclonal antibody (mAb)-mediated cross-linking of NTB-A results in the induction of NK-mediated cytotoxicity. Similar to 2B4 (CD244) functioning as a coreceptor in the NK cell activation, NTB-A also triggers cytolytic activity only in NK cells expressing high surface densities of natural cytotoxicity receptors. This suggests that also NTB-A may function as a coreceptor in the process of NK cell activation. Molecular cloning of the cDNA coding for NTB-A molecule revealed a novel member of the immunoglobulin superfamily belonging to the CD2 subfamily. NTB-A is characterized, in its extracellular portion, by a distal V-type and a proximal C2-type domain and by a cytoplasmic portion containing three tyrosine-based motifs. NTB-A undergoes tyrosine phosphorylation and associates with the Src homology 2 domain-containing protein (SH2D1A) as well as with SH2 domain-containing phosphatases (SHPs). Importantly, analysis of NK cells derived from patients with X-linked lymphoproliferative disease (XLP) showed that the lack of SH2D1A protein profoundly affects the function not only of 2B4 but also of NTB-A. Thus, in XLP-NK cells, NTB-A mediates inhibitory rather than activating signals. These inhibitory signals are induced by the interaction of NTB-A with still undefined ligands expressed on Epstein-Barr virus (EBV)-infected target cells. Moreover, mAb-mediated masking of NTB-A can partially revert this inhibitory effect while a maximal recovery of target cell lysis can be obtained when both 2B4 and NTB-A are simultaneously masked. Thus, the altered function of NTB-A appears to play an important role in the inability of XLP-NK cells to kill EBV-infected target cells.

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.

NK cells at the interface between innate and adaptive immunity.

In recent years a novel concept has emerged indicating that the actual role of natural killer (NK) cells is not confined to the destruction of virus-infected cells or tumors. Indeed, different NK subsets exist that display major functional differences in their cytolytic activity, cytokine production and homing capabilities. In particular, CD56(high) CD16(-) NK cells that largely predominate in lymph nodes, have little cytolytic activity but release high levels of cytokines whereas CD56(low) CD16(+) NK cells that predominate in peripheral blood and inflamed tissues, display lower cytokine production, but potent cytotoxicity. The latter is characterized by granule polarization and exocytosis of various proteins including perforin and granzymes that mediate target cell killing. The recruitment of CD56(low) CD16(+) NK cells into inflamed peripheral tissues is orchestrated by various chemochines including the newly identified Chemerin. At these sites, NK cells, upon engagement of different triggering receptors become activated and upregulate their cytokine production and cytotoxicity after interaction with myeloid dendritic cells (DCs). Importantly, during this interaction NK cells also mediate the 'editing' of DCs undergoing maturation. This process appears to play a crucial role in shaping both innate and adaptive immune responses. Indeed, only DCs undergoing this NK-mediated quality control would become fully mature and capable of inducing priming of protective Th1 responses.

Fetal size and growth velocity in chronic hypertension.

OBJECTIVE: To investigate longitudinal fetal growth and growth velocity for commonly measured biometric parameters in women with chronic hypertension. METHODS: Two centre retrospective European study of women with chronic hypertension ascertained at pregnancy booking. Ultrasound measurements of head circumference (HC), abdominal circumference (AC) and femur length (FL) were used to derive longitudinal fetal growth charts derived using functional linear discriminant analysis (FLDA). These were compared to existing cross sectional and longitudinal charts, as was birthweight. RESULTS: 282 women with a median of 3 third trimester ultrasound examinations were included. Gestation at delivery was 37.5weeks (SD 2.68), birthweight 3049g (SD 785). Birthweight <10th percentile found in 15.6% deliveries, >90th percentile 20.2%. Fetal size curves derived from women with chronic hypertension were no different to cross sectional and longitudinal charts for a normal population. Compared to a standard longitudinal biometry chart, growth velocity (mm/day) in chronic hypertension was higher for AC and FL at 30-32weeks (AC 1.447vs 1.357 p<0.05; FL 0.296vs 0.269 p<0.01) and 34-36weeks (AC 1.325vs 1.140 p<0.01; FL 0.248vs 0.198 p<0.01). CONCLUSIONS: In women with chronic hypertension there is an excess of both SGA and LGA babies compared to population standards. Growth velocity of the AC and FL was greater after 30weeks compared to a normal population.

Growth advantage and vascularization induced by basic fibroblast growth factor overexpression in endometrial HEC-1-B cells: an export-dependent mechanism of action.

The human endometrial adenocarcinoma HEC-1-B cell line was transfected with an expression vector harboring the human basic fibroblast growth factor (bFGF) cDNA under the control of the human beta-actin gene promoter. Stable transfectants were obtained in which a constitutive, limited overexpression of M(r) 24,000, 22,000, and 18,000 bFGF isoforms was observed. When transfectants were screened for the capacity to release the growth factor, significant amounts of bFGF were present in the conditioned medium and extracellular matrix of the bFGF-B9 clone but not of the bFGF-A8 clone, even though both cell lines produced similar levels of intracellular bFGF. When compared to parental cells, bFGF-B9 cells showed down-regulation of tyrosine kinase fibroblast growth factor receptors along with up-regulation of urokinase-type plasminogen activator expression which was abolished by incubation of the cell cultures with neutralizing anti-bFGF antibody. In vivo, bFGF-B9 cells formed highly vascularized tumors growing faster than parental cells when injected s.c. in nude mice. Also, they were more potent than nontransfected cells in inducing an angiogenic response in the rabbit cornea assay. In contrast, the bFGF-A8 cell phenotype was indistinguishable from parental cells both in vitro and in vivo. In conclusion, clonal differences exist within the HEC-1-B cell line in the capacity to release bFGF. bFGF export by human endometrial adenocarcinoma cells results in autocrine and paracrine effects that confer a growth advantage in vivo associated with increased neovascularization.

Involvement of natural cytotoxicity receptors in human natural killer cell-mediated lysis of neuroblastoma and glioblastoma cell lines.

The surface receptors involved in natural killer (NK) cell triggering during the process of target cell lysis have been at least in part identified. These are members of a novel family of receptors that has been termed natural cytotoxicity receptors (NCR). The first three members of this emerging group of receptors are the NKp46, NKp44 and NKp30 molecules that all belong to the immunoglobulin superfamily. Blocking of these receptors inhibits NK-mediated cytotoxicity against a wide variety of tumor target cells. In the present study, we show that these NCR are also involved in NK-mediated killing of tumor cells of neural origin. Glioblastoma and neuroblastoma target cells were efficiently killed by all NK clones analyzed since little protection from NK lysis was mediated by HLA class I molecules. Blocking of one or another NCR inhibited cytotoxicity; however, optimal inhibition was only observed when the three receptors were blocked simultaneously. A sharp difference in cytotoxicity against neural tumors was demonstrated between NCR(bright) and NCR(dull) NK clones, further supporting the notion that NCR play a critical role in the induction of cytotoxicity against tumor target cells of different histotype. Finally, our data also indicate that CD16 does not function as a triggering receptor involved in lysis of neural tumors since no difference in cytotoxicity could be substantiated between CD16(+) and CD16(-) NK clones and no correlation could be detected between the NCR(bright)/NCR(dull) phenotype and CD16 expression.

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.

Cellular and molecular pathogenesis of X-linked lymphoproliferative disease.

In the past few years important advances have been made in the understanding of the molecular mechanisms leading to X-linked lymphoproliferative disease (XLP). It has been possible to identify the gene defective in XLP and to demonstrate that, in normal individuals, it encodes the Src homology 2 domain-containing protein 1 A (SH2D1A) that plays a crucial role in signaling via a number of surface molecules expressed by cells of the immune system. At present a variety of mutations have been identified that result in lack of defective SH2D1A molecules. Importantly, it has recently been demonstrated that lack of SH2D1A affects the function of surface molecules that are involved in the mechanism of natural killer-mediated recognition and killing of Epstein-Barr virus-infected B cells.

Immunocytochemical localization of plasminogen activators in carcinomas in the cervix and vulva.

The presence of plasminogen activators (PA) in a variety of solid tumours appears to correlate, in a number of instances, with enhanced invasive and/or metastatic ability. Urokinase and tissue-type plasminogen activators (u-PA and t-PA) in normal and neoplastic tissues of cervix and of vulva were immunohistochemically identified by means of polycyclonal antibodies. In addition, frozen sections were analysed for u-PA and t-PA activity by in-situ zymography technique. Data collected in our study showed that in invasive cancer u-PA increased more in malignant cells as compared to normal cells in both the inactive and active enzymatic forms. The t-PA distribution pattern was related to angiogenesis while it did not relate to the degree of tumor differentiation. A synergic interaction between proteolytic tumoral activity and proteolytic inflammatory action could be hypothesized.

[Distribution of laminin, type IV collagen and fibronectin in normal, dysplastic and neoplastic laryngeal tissue]. / Distribuzione di laminina, collagene di tipo IV e fibronectina nel tessuto laringeo normale, displastico e neoplastico.

The main components, both intrinsic (laminin and type IV collagen) and extrinsic (fibronectin), of the basement membrane (BM) were analyzed by immunohistochemical methods in normal, dysplastic and neoplastic laryngeal mucosa specimens. The material was obtained from 35 patients who had undergone surgery for glottic or supraglottic cancer. Fibronectin proved to be absent from normal mucosa whereas an immunopositivity was observed close to the dysplastic epithelium, especially around inflammatory cells. Positivity increased as the degree of dysplasia increased from LIN I to LIN III. A strong staining was also seen around nests of well and moderately differentiated squamous cell carcinoma. These findings are in agreement with the theories about the main sites of origin for fibronectin, both from plasma and connective tissue. Laminin and type IV collagen showed the same staining characteristics. In normal and mild dysplastic samples a regular and continuous positivity was found at the boundaries between the epithelium and the mesenchymal stroma. Focal discontinuities were present in areas of intense subepithelial inflammation only. Interruptions and reduplications were more evident in severely dysplastic epithelium. In invasive squamous cell carcinomas a strong correlation has been found between the degree of cell differentiation and the pattern of distribution of the intrinsic BM components. Immunostaining was usually evident and continuous around nests of well differentiated squamous cell carcinoma, whereas positivity progressively decreased in moderately and poorly differentiated neoplasms. Furthermore, staining for intrinsic BM components was also related to the pattern of tumor growth: continuous around the "pushing" edge of neoplastic growth and discontinuous when the neoplastic front had an "invading" appearance. These observations tend to support the theory which considers neoplastic growth a cyclic process. BM components are most likely synthesized during the phases of quiescence and reabsorbed during the phase of invasiveness, following shifts in neoplastic cell metabolism.

Development of chicken embryos exposed to an intermittent horizontal sinusoidal 50 Hz magnetic field.

The effects of intermittent exposure (2 h on/22 h off) to a 200 microT horizontal, sinusoidally oscillating (50 Hz) magnetic field were studied in 210 fertilized chicken eggs. Two hundred ten control eggs (sham-exposed) were incubated in the same chamber as the experimental eggs. Chick embryos were examined for developmental anomalies and maturity stage after 48 h of incubation. Immunohistochemical analysis of extracellular membrane components (laminin, fibronectin, and type IV collagen) were conducted on day 7 and histological examinations for malformations of brain, liver, and heart, on days 7, 12, and 18 of incubation. Furthermore, egg fertility and egg weights were evaluated on days 2, 7, 12, and 18. The investigation also measured the body weight of chickens for 90 days from hatching and included histological analysis of body organs. Each variable was investigated blind. Statistical comparison between exposed and sham-exposed values did not show significant differences in any of the variables investigated. Thus, it appears that the exposure of embryos to an intermittent 200 microT magnetic field at 50 Hz does not cause developmental anomalies, changes in maturity stage, alterations in distribution of extracellular membrane components, or malformations in the brain, liver, or heart. Moreover, there were no differences in body weight, morphology, or histology of central nervous system, liver, heart, or testis in 90-day-old chickens hatched from exposed in comparison to sham-exposed eggs.

Function and specificity of human natural killer cell receptors.

In humans, natural killer lymphocytes express HLA class I-specific inhibitory receptors belonging to at least two different molecular families. The first is represented by members of the Ig superfamily that are involved in the recognition of different groups of HLA class I alleles, and the second is represented by a molecular complex formed by CD94 and NKG2A that displays a broad specificity for various class I molecules including the 'non-classical' HLA-G molecules. In addition to the inhibitory receptors, a series of activating receptors has been identified. Some display the same specificities as the corresponding inhibiting receptors and can be viewed as HLA class I-specific activating receptors. Another group of activating receptors appear to be involved in the cytolytic activity against HLA-'negative' target cells. These receptors are clearly non-MHC specific and, under physiological conditions, their function is suppressed by the HLA class I-specific inhibitory receptors.

2B4 functions as a co-receptor in human NK cell activation.

Natural cytotoxicity receptors (NKp46, NKp44 and NKp300) play a predominant role in human NK cell triggering during natural cytotoxicity. Human 2B4 also induced NK cell activation in redirected killing assays using anti-2B4 monoclonal antibodies (mAb) and murine targets. Since this effect was confined to a fraction of NK cells, this suggested a functional heterogeneity of 2B4 molecules. Here we show that activation via 2B4 in redirected killing against murine targets is strictly dependent upon the engagement of NKp46 by murine ligand (s) on target cells. Thus, NK cell clones expressing high surface density of NKp46 (NKp46bright) were triggered by anti-2B4 mAb, whereas NKp46dull clones were not although they expressed a comparable surface density of 2B4. mAb-mediated modulation of NKp46 molecules in NKp46bright clones had no effect on the expression of 2B4 while it rendered cells unresponsive to anti-2B4 mAb. Finally, anti-2B4 mAb could induce NK cell triggering in NKp46dull clones provided that suboptimal doses of anti-NKp44 or anti-CD16 mAb were added to the redirected killing assay. These results indicate that differences in responses do not reflect a functional heterogeneity of 2B4 but rather depend on the co-engagement of triggering receptors.

CD94 functions as a natural killer cell inhibitory receptor for different HLA class I alleles: identification of the inhibitory form of CD94 by the use of novel monoclonal antibodies.

CD94 molecules have been suggested to function as inhibitory natural killer cell (NK) receptors involved in the recognition of HLA-B alleles sharing the Bw6 supertypic specificity. In this study, we show that CD94 molecules may play a more general role: they are also involved in the recognition of other HLA class I molecules, including HLA-C and at least some HLA-A alleles. The inhibitory effect mediated by CD94 molecules on NK cytolytic activity is lower in magnitude than that of bona fide inhibitory receptors such as p58 or p70. Distinct from the other human NK receptors involved in HLA class I recognition, CD94 is expressed on virtually all NK cells. In addition, it has been shown to be functionally heterogeneous since, in different clones, CD94 mediated either cell triggering or inhibition. Although NK cells expressing inhibitory CD94 molecules are usually characterized by a CD94bright phenotype, there is no precise correlation between fluorescence intensity and inhibitory or activating function. Here, we describe two novel monoclonal antibodies (mAb) which selectively recognize inhibitory CD94 molecules and bind to a subset (variable in size among different donors) of CD94bright cells. The use of these mAb allows the direct assessment of NK cells expressing inhibitory CD94 receptors both at the population and at the clonal level.