Diagnostic des pathologies liées au virus Epstein-Barr

Epstein-Barr virus (EBV), a member of the Herpesviridae familly, infects most human (95 % of the world population). In immunocompetent hosts primary infection results in acute infectious mononucleosis. In immunocompromised hosts, EBV is associated with lymphoproliferative disorders which occur with an incidence 30 to 50 higher than in the immunocompetent host. The laboratory diagnosis of an EBV infection is based on two techniques : demonstration of the virus by viral antigen or viral DNA detection and serologic responses. Direct culture of the virus on B lymphocytes is time consuming and is not of general use.     

Diagnostic histopathologique de la mononucléose infectieuse

Infectious mononucleosis corresponds to the clinical syndrome of primary infection by Epstein-Barr virus (EBV). When diagnosis has not been achieved, pathologists may have to analyze lymph node biopsy, tonsil sample or spleen. In all cases, the diagnosis is based on a massive proliferation of infected B cells and cytotoxic T cells. Tissue architecture is preserved, sometimes masked by the polymorphic cellular infiltration, comprising many cells with plasmacytic differentiation. Immunohistochemistry shows the mixture of B and T immunoblasts, the polytypic phenotype of cells with plasmacytic differentiation and numerous cytotoxic T cells. EBV is evidenced by in situ hybridization (EBER-1 probe) or by immunohistochemistry with detection of latent viral proteins (LMP-1, EBNA-2). Differential diagnosis can be difficult with some lymphomas (Hodgkin's disease, Diffuse large B cell lymphomas…) as well as with other infectious chronic lymphadenopathies.     

Virus epstein-barr et proliférations lymphoïdes B

EBV driven B-cell lymphoid proliferations occur after the dysfunction of the immune control and they appear in primary or acquired immunodeficiencies. In primary immunodeficiencies, combined variable immune deficiency (CVID), X linked lymphoproliferative disorder (XLP), severe combined immune deficiency (SCID) and Wiskott-Aldrich syndrome (WAS) are frequently associaterd with EBV associated B-cell lymphoproliferative disorders or lymphomas. In acquired immunodeficiency after organ or bone marrow transplantation, the occurrence of lymphoid proliferation is one of the most serious complications. They are B-cell, polymorphic or monomorphic and EBV related in almost all cases in early proliferations after the graft. In HIV infection, EBV associated B-cell lymphoma are mostly observed in profound immunosuppressed patients. They are localised in brain or in other extra nodal sites. They are diffuse large B cell lymphoma having the features of immunoblastic subcategory. HIV related Burkitt lymphoma is associated with EBV in 30 to 70 % of cases. The role of EBV in such lymphoma where oncogenic events are predominant remain to be elucidated as well as in the Burkitt lymphoma occurring in immunocompetent patients (children or adults) where EBV is present in about 15 % of non endemic cases.     

Virus epstein-barr et système immunitaire

Epstein-Barr virus persists in CD27+ resting memory B cells of infected people. In lymph nodes, expression of latency II EBV program allows long term survival of EBV infected B cells. Sometimes a lymphoproliferation occurs due to the expression of latency III program which is associated with viral lytic cycle. This escape is usually controlled by the immune system and leads only to asymptomatic viral excretion in immunocompetent people. The control of EBV infection is mainly achieved with specific cellular immune response. Cytotoxic T CD8 lymphocytes (CTLs) were the first studied and their clinical significance has been demonstrated in transplanted patients in whom they prevent or allow the regression of EBV associated lymphoproliferations.CTLs detect lytic antigens with a high frequency during acute mononucleosis and persist thereafter during the latent infection. CTLs also detect latent antigens, however the frequency and intensity of response are lower in that case. Many epitopes have been described for the EBNA3 group proteins while LMP1, LMP2 a et b and EBNA LP proteins present just a few epitopes and induce moderate responses. EBNA 1 protein escapes to CTLs detection because it is not presented by the major histocompatibility complex class I. EBNA1 seems, however, to induce Th1 TCD4 response. T CD4 lymphocytes (TCD4) detect also EBNA3 proteins. Furthermore TCD4 play another role in EBV cycle, and this through cooperation with B lymphocyte (LB); indeed the CD40ligand of TCD4 interacts with the CD40 of LB.This interaction is necessary to obtain specific TCD4 and TCD8 responses and seems to play a key role in the reactivation of the EBV lytic cycle. Further studies should shed light on the interactions between EBV and TCD4 and determine the respective roles of responses toward latent and lytic antigens. Current data on the EBV specific immune response have already allowed to consider new therapeutic strategies for EBV associated lymphoproliferations by the restoration of cytotoxic responses against one or many epitopes.     

Virus epstein-barr et pathologies épithéliales et conjonctives

Besides the lymphoid proliferations, the Epstein-Barr virus (EBV) has been detected within a wide variety of pathological tissues over the last years, due largely to the application of modern viral detection techniques. We present here the epithelial andmesenchymal EBV-associated neoplasms.     

Exome sequencing identifies frequent mutation of ARID1A in molecular subtypes of gastric cancer

Gastric cancer is a heterogeneous disease with multiple environmental etiologies and alternative pathways of carcinogenesis. Beyond mutations in TP53, alterations in other genes or pathways account for only small subsets of the disease. We performed exome sequencing of 22 gastric cancer samples and identified previously unreported mutated genes and pathway alterations; in particular, we found genes involved in chromatin modification to be commonly mutated. A downstream validation study confirmed frequent inactivating mutations or protein deficiency of ARID1A, which encodes a member of the SWI-SNF chromatin remodeling family, in 83% of gastric cancers with microsatellite instability (MSI), 73% of those with Epstein-Barr virus (EBV) infection and 11% of those that were not infected with EBV and microsatellite stable (MSS). The mutation spectrum for ARID1A differs between molecular subtypes of gastric cancer, and mutation prevalence is negatively associated with mutations in TP53. Clinically, ARID1A alterations were associated with better prognosis in a stage-independent manner. These results reveal the genomic landscape, and highlight the importance of chromatin remodeling, in the molecular taxonomy of gastric cancer.     

Apoptose et virus (hormis les rétrovirus)

Apoptosis is a genetically preprogrammed cellular event which can be repressed by survival genes or activated by death genes. Numerous viral gene products bind to these genes or are homologous in sequence and function with them and block or mimic their activities, for example proteins of adenovirus and of Epstein-Barr virus (EBV). First, the initial signal for apoptosis activation, which is mediated by Fas/Apo1/TNFR complex, can be inhibited by proteins from adenovirus (E1B 19 kDa and E3), from myxomavirus (MT2), from baculovirus (iap), from herpes simplex virus and cytomegalovirus, and induced by myxoviruses, hepatitis C virus and cytomegalovirus. Secondly, the transduction of the signal to the genes of the cell death machinery (p53, pRB, bcl-2) and the transactivation of the cellular protooncogenes (c-myc, c-fos, c-jun) can be inhibited by proteins from adenovirus (E1B 19 kDa), from EBV (BHRF1, LMP1, BZLF1, EBNA-5LP), from herpesvirus (orf16), from baculovirus (p35), from cytomegalovirus (IE1/IE2/IE86), from SV40 (T), from hepatitis B virus (pX) and from papillomavirus (E6) or induced by proteins from adenovirus (E1A), from herpes simplex type 1 (VP16), from papillomavirus (E7), from polyomavirus (T), from EBV (EBNA-5), from chicken anemia virus (VP3) and from B19 parvovirus (NS1). Third, the effector phase of apoptosis which includes the proteases (caspases) can be inhibited by proteins from cowpoxvirus (crmA) and from baculovirus (p53) or induced by Sindbis virus, coxsackievirus B3, arteriviridae and dengue virus. Early cell death limits virus production, reduces spread of progeny viruses and results in virus clearance under CTL activity. Delayed apoptosis at late stages of infection, allows production and spread of high yields of progeny viruses, evading host immune inflammatory responses and protecting progeny viruses from host enzymes and antibodies. Inhibition of apoptosis contributes to the maintenance of viral latency or to cell transformation. Such virally induced apoptosis may also contribute to pathogenesis and treatment of viral diseases.     

Techniques biologiques du diagnotic anténatal des infections virales et de la toxoplasmose

The main infections prenatally detected in fetuses are : cytomegalovirus parvovirus B19, rubella virus, and varicella-zoster infections. Today, prenatal diagnosis is currently performed after detection of maternal primary infection or because of abnormal ultrasound findings. Diagnosis of maternal primary infection is essentially based on the detection of specific IgM antibodies, but it was greatly improved by the use of complementary tests such as the measurement of the IgG avidity index.Prenatal diagnosis is based on the direct detection of the microorganism (CMV, toxoplasma), of its antigens (CMV) or of its genome. This direct detection can be done either on fetal blood or on amniotic fluid. Prenatal diagnosis can also be performed by detection of specific IgM in fetal blood (rubella). Non specific markers of fetal infection can also help in diagnosis. At the present time, prenatal diagnosis is essentially based on the detection of the genome in amniotic fluid.     

Innate partnership of HLA-B and KIR3DL1 subtypes against HIV-1

Allotypes of the natural killer (NK) cell receptor KIR3DL1 vary in both NK cell expression patterns and inhibitory capacity upon binding to their ligands, HLA-B Bw4 molecules, present on target cells. Using a sample size of over 1,500 human immunodeficiency virus (HIV)+ individuals, we show that various distinct allelic combinations of the KIR3DL1 and HLA-B loci significantly and strongly influence both AIDS progression and plasma HIV RNA abundance in a consistent manner. These genetic data correlate very well with previously defined functional differences that distinguish KIR3DL1 allotypes. The various epistatic effects observed here for common, distinct KIR3DL1 and HLA-B Bw4 combinations are unprecedented with regard to any pair of genetic loci in human disease, and indicate that NK cells may have a critical role in the natural history of HIV infection.     

Epistasis between mouse Klra and major histocompatibility complex class I loci is associated with a new mechanism of natural killer cell-mediated innate resistance to cytomegalovirus infection

Experimental infection with mouse cytomegalovirus (MCMV) has been used to elucidate the intricate host-pathogen mechanisms that determine innate resistance to infection. Linkage analyses in F(2) progeny from MCMV-resistant MA/My (H2 (k)) and MCMV-susceptible BALB/c (H2 (d)) and BALB.K (H2 (k)) mouse strains indicated that only the combination of alleles encoded by a gene in the Klra (also called Ly49) cluster on chromosome 6, and one in the major histocompatibility complex (H2) on chromosome 17, is associated with virus resistance. We found that natural killer cell-activating receptor Ly49P specifically recognized MCMV-infected cells, dependent on the presence of the H2 (k) haplotype. This binding was blocked using antibodies to H-2D(k) but not antibodies to H-2K(k). These results are suggestive of a new natural killer cell mechanism implicated in MCMV resistance, which depends on the functional interaction of the Ly49P receptor and the major histocompatibility complex class I molecule H-2D(k) on MCMV-infected cells.     

ATP-sensitive potassium channels mediate survival during infection in mammals and insects

Specific homeostatic mechanisms confer stability in innate immune responses, preventing injury or death from infection. Here we identify, from a screen of N-ethyl-N-nitrosourea-mutagenized mice, a mutation causing both profound susceptibility to infection by mouse cytomegalovirus and approximately 20,000-fold sensitization to lipopolysaccharide (LPS), poly(I.C) and immunostimulatory (CpG) DNA. The LPS hypersensitivity phenotype is not suppressed by mutations in Myd88, Trif, Tnf, Tnfrsf1a, Ifnb, Ifng or Stat1, genes contributing to LPS responses, and results from an abnormality extrinsic to hematopoietic cells. The phenotype is due to a null allele of Kcnj8, encoding Kir6.1, a protein that combines with SUR2 to form an ATP-sensitive potassium channel (K(ATP)) expressed in coronary artery smooth muscle and endothelial cells. In Drosophila melanogaster, suppression of dSUR by RNA interference similarly causes hypersensitivity to infection by flock house virus. Thus, K(ATP) evolved to serve a homeostatic function during infection, and in mammals it prevents coronary artery vasoconstriction induced by cytokines dependent on TLR and/or MDA5 immunoreceptors.     

The persistence of a silent memory

One of the most striking properties of RNA interference (RNAi) in Caenorhabditis elegans is its persistence in offspring after the triggering double-stranded RNA (dsRNA) has disappeared. A new study reveals that a heterochromatic silencing mark is deposited around the targets of RNAi and is transmitted through generations. These results show that RNAi can induce stable and heritable chromatin modifications in animals.     

Epistatic interaction between KIR3DS1 and HLA-B delays the progression to AIDS

Natural killer (NK) cells provide defense in the early stages of the innate immune response against viral infections by producing cytokines and causing cytotoxicity. The killer immunoglobulin-like receptors (KIRs) on NK cells regulate the inhibition and activation of NK-cell responses through recognition of human leukocyte antigen (HLA) class I molecules on target cells KIR and HLA loci are both highly polymorphic, and some HLA class I products bind and trigger cell-surface receptors specified by KIR genes. Here we report that the activating KIR allele KIR3DS1, in combination with HLA-B alleles that encode molecules with isoleucine at position 80 (HLA-B Bw4-80Ile), is associated with delayed progression to AIDS in individuals infected with human immunodeficiency virus type 1 (HIV-1). In the absence of KIR3DS1, the HLA-B Bw4-80Ile allele was not associated with any of the AIDS outcomes measured. By contrast, in the absence of HLA-B Bw4-80Ile alleles, KIR3DS1 was significantly associated with more rapid progression to AIDS. These observations are strongly suggestive of a model involving an epistatic interaction between the two loci. The strongest synergistic effect of these loci was on progression to depletion of CD4(+) T cells, which suggests that a protective response of NK cells involving KIR3DS1 and its HLA class I ligands begins soon after HIV-1 infection.     

Analysis of the coding genome of diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common form of human lymphoma. Although a number of structural alterations have been associated with the pathogenesis of this malignancy, the full spectrum of genetic lesions that are present in the DLBCL genome, and therefore the identity of dysregulated cellular pathways, remains unknown. By combining next-generation sequencing and copy number analysis, we show that the DLBCL coding genome contains, on average, more than 30 clonally represented gene alterations per case. This analysis also revealed mutations in genes not previously implicated in DLBCL pathogenesis, including those regulating chromatin methylation (MLL2; 24% of samples) and immune recognition by T cells. These results provide initial data on the complexity of the DLBCL coding genome and identify novel dysregulated pathways underlying its pathogenesis.