Expression of EBV/C3d receptors on T cells: biological significance

Advances and applications of RNA vaccines in tumor treatment

Compared to other types of tumor vaccines, RNA vaccines have emerged as promising alternatives to conventional vaccine therapy due to their high efficiency, rapid development capability, and potential for low-cost manufacturing and safe drug delivery. RNA vaccines mainly include mRNA, circular RNA (circRNA), and Self-amplifying mRNA(SAM). Different RNA vaccine platforms for different tumors have shown encouraging results in animal and human models. This review comprehensively describes the advances and applications of RNA vaccines in antitumor therapy. Future directions for extending this promising vaccine platform to a wide range of therapeutic uses are also discussed.

CD21 (Complement Receptor 2) Is the Receptor for Epstein-Barr Virus Entry into T Cells

Epstein-Barr virus (EBV) is associated with a number of T-cell diseases, including some peripheral T-cell lymphomas, hemophagocytic lymphohistiocytosis, and chronic active EBV disease. The tropism of EBV for B cells and epithelial cell infection has been well characterized, but infection of T cells has been minimally explored. We have recently shown that the EBV type 2 (EBV-2) strain has the unique ability to infect mature T cells. Utilizing an ex vivo infection model, we sought to understand the viral glycoprotein and cellular receptor required for EBV-2 infection of T cells. Here, using a neutralizing-antibody assay, we found that viral gp350 and complement receptor 2 (CD21) are required for CD3⁺ T-cell infection. Using the HB5 anti-CD21 antibody clone but not the Bly-4 anti-CD21 antibody clone, we detected expression of CD21 on both CD4⁺ and CD8⁺ T cells, with the highest expression on naive CD4 and CD8⁺ T-cell subsets. Using CRISPR to knock out CD21, we demonstrated that CD21 is necessary for EBV entry into the Jurkat T-cell line. Together, these results indicate that EBV uses the same viral glycoprotein and cellular receptor for both T- and B-cell infection.IMPORTANCE Epstein-Barr virus (EBV) has a well-described tropism for B cells and epithelial cells. Recently, we described the ability of a second strain of EBV, EBV type 2, to infect mature peripheral T cells. Using a neutralizing antibody assay, we determined that EBV uses the viral glycoprotein gp350 and the cellular protein CD21 to gain entry into mature peripheral T cells. CRISPR-Cas9 deletion of CD21 on the Jurkat T-cell line confirmed that CD21 is required for EBV infection. This study has broad implications, as we have defined a function for CD21 on mature peripheral T cells, i.e., as a receptor for EBV. In addition, the requirement for gp350 for T-cell entry has implications for EBV vaccine studies currently targeting the gp350 glycoprotein to prevent EBV-associated diseases.

Intracellular complement activation-An alarm raising mechanism?

It has become increasingly apparent that the complement system, being an ancient defense mechanism, is not operative only in the extracellular milieu but also intracellularly. In addition to the known synthetic machinery in the liver and by macrophages, many other cell types, including lymphocytes, adipocytes and epithelial cells produce selected complement components. Activation of e.g. C3 and C5 inside cells may have multiple effects ranging from direct antimicrobial defense to cell differentiation and possible influence on metabolism. Intracellular activation of C3 and C5 in T cells is involved in the maintenance of immunological tolerance and promotes differentiation of T helper cells into Th1-type cells that activate cell-mediated immune responses. Adipocytes are unique in producing many complement sensor proteins (like C1q) and Factor D (adipsin), the key enzyme in promoting alternative pathway amplification. The effects of complement activation products are mediated by intracellular and cell membrane receptors, like C3aR, C5aR1, C5aR2 and the complement regulator MCP/CD46, often jointly with other receptors like the T cell receptor, Toll-like receptors and those of the inflammasomes. These recent observations link complement activation to cellular metabolic processes, intracellular defense reactions and to diverse adaptive immune responses. The complement components may thus be viewed as intracellular alarm molecules involved in the cellular danger response.

C3d regulates immune checkpoint blockade and enhances antitumor immunity

Despite expression of immunogenic polypeptides, tumors escape immune surveillance by engaging T cell checkpoint regulators and expanding Tregs, among other mechanisms. What orchestrates these controls is unknown. We report that free C3d, a fragment of the third component of complement, inside tumor cells - or associated with irradiated tumor cells and unattached to antigen - recruits, accelerates, and amplifies antitumor T cell responses, allowing immunity to reverse or even to prevent tumor growth. C3d enhances antitumor immunity independently of B cells, NK cells, or antibodies, but it does so by increasing tumor infiltrating CD8+ lymphocytes, by depleting Tregs, and by suppressing expression of programmed cell death protein 1 (PD-1) by T cells. These properties of C3d appear specific for the tumor and dependent on complement receptor 2, and they incur no obvious systemic toxicity. The heretofore unrecognized properties of free C3d suggest that protein might determine the effectiveness of immune surveillance and that increasing availability of the protein might prove advantageous in the treatment or prevention of cancer and premalignant conditions.

C3 promotes expansion of CD8+ and CD4+ T cells in a Listeria monocytogenes infection

It is known that C3 is required for optimal expansion of T cells during acute viral infections. However, it is not yet determined whether T cell responses to intracellular bacterial infections require C3. Therefore, we have investigated the requirement for C3 to elicit potent T cell responses to Listeria monocytogenes (LM). We show that expansion of Ag-specific CD8 and CD4 T cells during a primary response to LM was markedly reduced in the absence of C3 activity. Further studies indicated that, unlike in an influenza virus infection, the regulation of LM-specific T cell responses by C3 might not involve the downstream effector C5a. Moreover, reduced T cell responses to LM was not linked to defective maturation of dendritic cells or developmental anomalies in the peripheral T cell compartment of C3-deficient mice. Experiments involving adoptive transfer of C3-deficient CD8 T cells into the C3-sufficient environment of wild-type mice showed that these T cells do not have intrinsic proliferative defects, and a paracrine source of C3 will suffice for clonal expansion of CD8 T cells in vivo. However, stimulation of purified C3-deficient CD8 T cells by plastic-immobilized anti-CD3 showed that C3 promotes T cell proliferation directly, independent of its effects on APC. On the basis of these findings, we propose that diminished T cell responses to LM in C3-deficient mice might be at least in part due to lack of direct effects of C3 on T cells. These studies have furthered our understanding of C3-mediated regulation of T cell immunity to intracellular pathogens.

Cutting edge: members of the Staphylococcus aureus extracellular fibrinogen-binding protein family inhibit the interaction of C3d with complement receptor 2

Staphylococcus aureus expresses a highly diversified arsenal of immune evasion proteins, many of which target the complement system. The extracellular fibrinogen-binding protein (Efb) and the Efb homologous protein (Ehp) have previously been demonstrated to bind to C3 and inhibit complement activation and amplification. In this study we present the first evidence that Efb and Ehp are also capable of inhibiting the interaction of C3d with complement receptor 2 (CR2), which plays an important role in B cell activation and maturation. The C-terminal domain of Efb efficiently blocked this interaction both in surface plasmon resonance-based competition studies and cellular assays and prevented the CR2-mediated stimulation of B cells. Furthermore, analyses of the available structural data were consistent with a molecular mechanism that reflects both steric and electrostatic effects on the C3d-CR2 interaction. Our study therefore suggests that S. aureus may disrupt both the innate and adaptive immune responses with a single protein module.

The spectrum of Epstein-Barr virus-associated lymphoproliferative disease in Korea: incidence of disease entities by age groups

This study is to identify the spectrum of Epstein-Barr virus (EBV)-positive lymphoproliferative diseases (LPD) and relationships between these diseases in Korea. The EBV status and clinicopathology of 764 patients, including acute EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH), chronic active EBV (CAEBV) infections, B-LPD arising in chronic latent EBV infection, T & natural killer (NK) cell non-Hodgkin's lymphomas (NHL), B-NHLs, and Hodgkin's lymphomas (HD), were analyzed. T or NK cell NHLs were the most common forms of EBV-positive NHLs (107/167, 64%); among these, nasal-type NK/T cell lymphomas were the most common (89/107, 83%). According to the age, Burkitt's lymphoma was the most common in early childhood; in teenagers, chronic (active) EBV infection-associated LPD was the most common type. The incidence of NK/T cell lymphoma began to increase from the twenties and formed the major type of EBV-associated tumor throughout life. Diffuse large B cell lymphoma formed the major type in the sixties and seventies. In conclusion, primary infections in early childhood are complicated by the development of CAEBV infections that are main predisposing factors for EBV-associated T or NK cell malignancies in young adults. In old patients, decreased immunity associated with old age and environmental cofactors may provoke the development of peripheral T cell lymphoma, unspecified, and diffuse large B cell lymphoma.

Complement evasion by human pathogens

The human immune system has developed an elaborate network of cascades for dealing with microbial intruders. Owing to its ability to rapidly recognize and eliminate microorganisms, the complement system is an essential and efficient component of this machinery. However, many pathogenic organisms have found ways to escape the attack of complement through a range of different mechanisms. Recent discoveries in this field have provided important insights into these processes on a molecular level. These vital developments could augment our knowledge of the pathology and treatment of infectious and inflammatory diseases.

The electrostatic nature of C3d-complement receptor 2 association

The association of complement component C3d with B or T cell complement receptor 2 (CR2 or CD21) is a link between innate and adaptive immunity. It has been recognized in experimental studies that the C3d-CR2 association is pH- and ionic strength-dependent. This led us to perform electrostatic calculations to obtain a theoretical understanding of the mechanism of C3d-CR2 association. We used the crystallographic structures of human free C3d, free CR2 (short consensus repeat (SCR)1-2), and the C3d-CR2(SCR1-2) complex, and continuum solvent representation, to obtain a detailed atomic-level picture of the components of the two molecules that contribute to association. Based on the calculation of electrostatic potentials for the free and bound species and apparent pK(a) values for each ionizable residue, we show that C3d-CR2(SCR1-2) recognition is electrostatic in nature and involves not only the association interface, but also the whole molecules. Our results are in qualitative agreement with experimental data that measured the ionic strength and pH dependence of C3d-CR2 association. Also, our results for the native molecules and a number of theoretical mutants of C3d explain experimental mutagenesis studies of amino acid replacements away from the association interface that modulate binding of iC3b with full-length CR2. Finally, we discuss the packing of the two SCR domains. Overall, our data provide global and site-specific explanations of the physical causes that underlie the ionic strength dependence of C3d-CR2 association in a unified model that accounts for all experimental data, some of which were previously thought to be contradictory.

Infection with an endemic human herpesvirus disrupts critical glial precursor cell properties

Human herpesvirus 6 (HHV-6), a common resident virus of the human CNS, has been implicated in both acute and chronic inflammatory--demyelinating diseases. Although HHV-6 persists within the human CNS and has been described to infect mature oligodendrocytes, nothing is known about the susceptibility of glial precursors, the ancestors of myelin-producing oligodendrocytes, to viral infection. We show that HHV-6 infects human glial precursor cells in vitro. Active infection was demonstrated by both electron microscopy and expression of viral gene transcripts and proteins, with subsequent formation of cell syncytia. Infection leads to alterations in cell morphology and impairment of cell replication but not increased cell death. Infected cells showed decreased proliferation as measured by bromodeoxyuridine uptake, which was confirmed by blunting of the cell growth rate of infected cells compared with uninfected controls over time. The detailed analysis using novel, fluorescent-labeled HHV-6A or HHV-6B reagents demonstrated strong G1/S phase inhibition in infected precursor cells. Cell cycle arrest in HHV-6-infected cells was associated with a profound decrease in the expression of the glial progenitor cell marker A2B5 and a corresponding increase in the oligodendrocyte differentiation marker GalC. These data demonstrate for the first time that infection of primary human glial precursor cells with a neurologically relevant human herpesvirus causes profound alterations of critical precursor cell properties. In light of recent observations that repair of CNS demyelination is dependent on the generation of mature oligodendrocytes from the glial precursor cell pool, these findings may have broad implications for both the ineffective repair seen in demyelinating diseases and the disruption of normal glial maturation.

Complement: structure, functions, evolution, and viral molecular mimicry

The complement (C') system has long been recognized as an important mediator of innate immune defense and inflammation. In recent years there is increasing evidence suggesting that complement components may also participate in non-inflammatory and developmental processes. Here we review our current work on the structural-functional aspects of C3-ligand interactions and the rational design of small-sized complement inhibitors. We present a novel, proteomics-based, approach to studying protein-protein interactions within the C' system and discuss our progress in the study of viral immune evasion strategies. Furthermore we discuss the involvement of complement proteins in organ regeneration and hematopoietic development.

Epstein-Barr virus: induction and control of cell transformation

Epstein-Barr virus (EBV), a ubiquitous human herpes virus, is associated with an increasing number of lymphoid and epithelial malignancies. The ability of the virus to establish life-long persistent infections and induce growth transformation is related to the function of a set of viral proteins that are variously expressed in both normal and malignant cells. Recent evidence indicates that these viral proteins are able to usurp cellular pathways that promote the cell growth and survival, while impairing anti-viral immune responses. Elucidation of the mechanisms by which EBV induces cell transformation and escapes host immune control provides the rational background for the design of new strategies of intervention for EBV-related malignancies.

Complement component 3 is required for optimal expansion of CD8 T cells during a systemic viral infection

In addition to its established role in innate immune mechanisms, complement component C3 is also of critical importance in B cell activation and T cell-dependent Ab responses. In this study, we have examined the requirement for C3 in the generation of primary CD8 T cell responses to an acute systemic viral infection. We compared Ag-specific CD8 T cell responses to lymphocytic choriomeningitis virus (LCMV) between wild-type (+/+) and C3-deficient (C3(-/-)) mice on both 129/B6 and B6 backgrounds. These studies revealed that C3 activity is required for optimal expansion of LCMV-specific effector CD8 T cells in an epitope-dependent fashion, which is influenced by the genetic background of the mice. Studies in complement receptor 1/2 (CR1/CR2)-deficient mice showed that regulation of LCMV-specific CD8 T cell responses by C3 is not dependent upon CR1/CR2. These findings may have implications in vaccine development, therapy of autoimmune diseases, and prevention of graft rejection.

Purification and characterization of soluble CD21 from human plasma by affinity chromatography and density gradient centrifugation

Complement receptor II (CD21) is the receptor for C3d fragments on immune complexes. It also serves as a receptor for Epstein-Barr virus (EBV) and on B-lymphocytes CD21 amplifies signalling through the B cell receptor. CD21 is shed from the surface of the cell and is found circulating in plasma. There, soluble CD21 (sCD21) binds to CD23 and complement fragments, thereby modulating the immune response. sCD21 activates monocytes through binding to membrane CD23. The clinical significance of sCD21 is shown by the increased levels found in the sera of patients with B lymphomas, EBV infections and other lymphoblastoid tumors. In this paper, we report the isolation of soluble CD21 from human plasma using affinity chromatography and density gradient centrifugation. sCD21 was found to be a single 126 kDa molecular species. By determining the sedimentation coefficient, we have calculated the partial specific volume, diffusion coefficient and frictional coefficient of the protein. These values show that the sCD21 isolated from human plasma is an elongated rod-shaped molecule.

Biological aspects of Epstein-Barr virus (EBV)-infected lymphocytes in chronic active EBV infection and associated malignancies

Most primary Epstein-Barr virus (EBV) infections are clinically inapparent, but occasionally EBV infection can cause acute infectious mononucleosis. EBV has been linked to a variety of hematologic and non-hematologic malignancies. Chronic active EBV (CAEBV) infection designates a recently identified EBV-associated syndrome characterized by a variety of serious hematological disorders, including malignant lymphoma. EBV was found to infect circulating T- and/or NK-cells in patients with CAEBV infection. These EBV-infected T- and/or NK-cells express EBNA-1, LMP-1, and LMP-2A, a type II form of EBV latency, which is also observed in nasopharyngeal carcinoma (NPC), Hodgkin's disease (HD), and peripheral T-cell lymphoma. CAEBV infections may thus represent a subset of EBV-associated T- and/or NK-cell lymphoproliferative disorders.

Epstein-Barr virus primes human polymorphonuclear leucocytes for the biosynthesis of leukotriene B4

In the present study, we have investigated the effect of the short-term incubation of polymorphonuclear leucocytes (PMN) with infectious Epstein-Barr virus (EBV) on leukotriene B(4) (LTB(4)) biosynthesis. Pre-exposure of PMN to EBV led to an increased production of LTB(4) upon stimulation with either the ionophore A23187, the chemotactic peptide fMLP, or phagocytic particles (zymosan). Experiments performed with viral particles pretreated with a neutralizing antibody raised against the gp350 of the viral envelope revealed that a specific interaction between the PMN surface and the viral glycoprotein gp350 is required for the priming effect of EBV. Preincubation of PMN with EBV resulted in an increased release of arachidonic acid upon stimulation with a second agonist. Moreover, LTB(4) biosynthesis in EBV/A23187-treated PMN was greatly diminished in the presence of an inhibitor of the cytosolic phospholipase A2 (cPLA(2)), suggesting that cPLA(2) plays a critical role in the priming effect of EBV. Accordingly, EBV by itself promoted Ser-505 phosphorylation of cPLA(2) and strongly enhanced fMLP-induced phosphorylation of p38 MAP kinase, an enzyme known to phosphorylate cPLA(2) in human PMN. Furthermore, fMLP-induced translocation of cPLA(2) was strongly enhanced when PMN were previously exposed to EBV. These data indicate that binding of EBV to human PMN results in the activation of intracellular events involved in the release of pro-inflammatory lipid mediators.

Epitope mapping using the X-ray crystallographic structure of complement receptor type 2 (CR2)/CD21: identification of a highly inhibitory monoclonal antibody that directly recognizes the CR2-C3d interface

Complement receptor type 2 (CR2)/CD21 is a B lymphocyte cell membrane C3d/iC3b receptor that plays a central role in the immune response. Human CR2 is also the receptor for the EBV viral membrane glycoprotein gp350/220. Both C3d and gp350/220 bind CR2 within the first two of 15-16 repetitive domains that have been designated short consensus/complement repeats. Many mAbs react with human CR2; however, only one currently available mAb is known to block both C3d/iC3b and gp350/220 binding. We have used a recombinant form of human CR2 containing the short consensus/complement repeat 1-2 ligand-binding fragment to immunize Cr2(-/-) mice. Following fusion, we identified and further characterized four new anti-CR2 mAbs that recognize this fragment. Three of these inhibited binding of CR2 to C3d and gp350/220 in different forms. We have determined the relative inhibitory ability of the four mAbs to block ligand binding, and we have used overlapping peptide-based approaches to identify linear epitopes recognized by the inhibitory mAbs. Placement of these epitopes on the recently solved crystal structure of the CR2-C3d complex reveals that each inhibitory mAb recognizes a site either within or adjacent to the CR2-C3d contact site. One new mAb, designated 171, blocks CR2 receptor-ligand interactions with the greatest efficiency and recognizes a portion of the C3d contact site on CR2. Thus, we have created an anti-human CR2 mAb that blocks the C3d ligand by direct contact with its interaction site, and we have provided confirmatory evidence that the C3d binding site seen in its crystal structure exists in solution.

Oligoclonal expansion of alphabeta T lymphocytes in Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis with abnormal karyotypes

We observed a fatal case of Epstein-Barr virus (EBV)-associated hemophagocytic lymphohistiocytosis (HLH) with an abnormal karyotype. Increased levels of alphabeta T cells of the patient were investigated using an inverse polymerase chain reaction (PCR) of the T-cell receptor variable region gene, followed by Jbeta-PCR and single-strand conformation polymorphism (SSCP) to confirm the clonality of specific alphabeta-T cell subsets. A high frequency (>15%) was recognized in Vbeta9 at onset, but not in any Vbeta and Valpha families 2 weeks after chemotherapy. High levels (>20%) of some Jbeta genes were detected in all Vbeta families investigated, and the predominant bias of the Jbeta2 gene relative to the Jbeta1 gene (86.1% versus 13.9% at onset, and 77.4% versus 23.5% after chemotherapy) was recognized in pan-alphabeta T cells. When each Vbeta-Jbeta fragment was compared among the samples at onset and after chemotherapy by SSCP analysis, several distinct bands were observed that indicate a clonal evolution. Thus, the findings suggest that some of the alphabeta T cell clones could be associated with abnormal karyotypes in EBV-HLH. The present findings provide molecular evidence of the presence of oligoclonal T cells in pan-alphabeta-T cells and clonal evolution during a short clinical course in EBV-HLH with abnormal karyotypes.

Kinetic analysis of the interactions of complement receptor 2 (CR2, CD21) with its ligands C3d, iC3b, and the EBV glycoprotein gp350/220

The molecular mechanisms involved in the interaction of complement receptor 2 (CR2) with its natural ligands iC3b and C3d are still not well understood. In addition, studies regarding the binding site(s) of the receptor on C3 as well as the affinities of the C3 fragments for CR2 have produced contradictory results. In the present study, we have used surface plasmon resonance technology to study the interaction of CR2 with its ligands C3d, iC3b, and the EBV surface glycoprotein gp350/220. We measured the kinetics of binding of the receptor to its ligands, examined the influence of ionic contacts on these interactions, and assessed whether immobilized and soluble iC3b bound with similar kinetics to CR2. Our results indicate that 1) gp350 binding to CR2 follows a simple 1:1 interaction, whereas that of the C3 fragments is more complex and involves more than one intramolecular component; 2) kinetic differences exist between the binding of C3d and iC3b to CR2, which may be due to an additional binding site found on the C3c region of iC3b; and 3) iC3b binds to CR2 with different kinetics, depending on whether the iC3b is in solution or immobilized on the surface. These findings suggest that binding of CR2 to iC3b and C3d is more complex than previously thought.

Multiple transcription factors regulate the inducible expression of the human complement receptor 2 promoter

Complement receptor 2 (CR2) is regulated at the transcriptional level, but the promoter elements and the transcription factors that bind to them and contribute to its regulation are unknown. After documenting that PMA and cAMP induced the activity of the CR2 promoter by 10-fold, we conducted promoter truncation and mutagenesis experiments, in conjunction with shift assays, to determine the functionally important regions of the promoter and the proteins that bind to them. We identified two regions, separated by approximately 900 nucleotides, which together were responsible for inducible promoter activity. Mutagenesis of single promoter elements demonstrated a functional upstream stimulatory factor/E box in the TATA box-proximal region and three equally important, closely spaced, CREB/AP-1 half-sites in the upstream promoter region. The cAMP response element-binding protein (CREB)/AP-1 half-sites bound in vitro Jun and CREB that are induced by protein kinases A and/or C. The 900-nucleotide segment stretching between the above two regions had no functional impact on the induced transcription, and its deletion increased the promoter activity. Finally, a region upstream of the distal site had a repressor activity on CR2 transcription. Moreover, IL-4 induced binding of CREB and AP-1 to the upstream promoter elements and resulted in increased CR2 surface protein expression. These studies have characterized regions of the CR2 promoter and the transcription factors that bind to them and are crucial to induced CR2 expression. Our studies may provide insights to novel approaches to modulate B cell function by regulating CR2 gene transcription.

A Hodgkin’s Disease Cell Line, KM-H2, Shows Biphenotypic Features of Dendritic Cells and B Cells

The origin of Reed-Sternberg (RS) cells, the neoplastic cells of Hodgkin's disease, has long remained controversial. Dendritic cells (DCs) are highly specialized antigen-presenting cells that have the unique capacity to prime naive T cells, and they may be progenitors of RS cells in a population of Hodgkin's disease cells. In this study, the KM-H2 cell line, previously established from a patient with Hodgkin's disease of mixed cellularity, was reevaluated for its cellular derivation, particularly in terms of DCs. KM-H2 cells were demonstrated to carry the newly proposed DC-associated molecules fascin, CD83, and DEC-205, as well as costimulatory molecules such as CD40, CD80, and CD86. In addition, KM-H2 cells were shown to be able to potently stimulate peripheral blood T cells and to have the strong endocytotic activity of fluorescein isothiocyanate-dextran. On the other hand, KM-H2 cells were shown to have variable-diversity-joining recombination of the immunoglobulin H gene, although they did not express any subclasses of immunoglobulin and they were negative for CD79a and CD79b. In addition, KM-H2 cells produced the messenger RNA of the Pax-5 gene. These findings lead to a hypothesis that KM-H2 cells originated from the cells that had differentiated through the possible common DC-B-cell progenitors along the newly proposed pathway.

The anti-human CD21 antibody, BU33, identifies equine B cells

The number of antibodies for identifying equine B cells is small and the number that react with well-defined epitopes even smaller. The monoclonal antibody, BU33, which is directed against human CD21 (Complement Receptor 2; CR2) was shown to identify (1) follicular lymphocytes in the lymph nodes and spleen of three horses, and (2) a mean of 18 +/- 6% (SEM) of peripheral blood lymphocytes from 10 horses. These findings indicate that the antibody identifies equine B cells and possibly equine CR2 or a related molecule. This study adds to the reagents available for equine research and diagnostic pathology.

Coreceptor restriction within the HLA-DQ locus for Epstein-Barr virus infection

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that causes infectious mononucleosis and is etiologically associated with malignancies of multiple origins. EBV enters cells through a cascade of interactions between its envelope glycoprotein gp350 and the gp42-gH-gL complex with cellular receptors. Membrane fusion is catalyzed by the binding of gp42, a member of the C type lectin family, to HLA class II molecule HLA-DR, -DP, or -DQ. Here we demonstrate that only a subset of HLA-DQ alleles mediates EBV entry, indicating that individuals expressing these alleles may offer unique sites for EBV infection and subsequent sequelae. Additionally, the specific site within HLA-DQ determined to be essential for EBV entry is homologous to a site within MHC class I shown by structural studies to bind to the C type-lectin-like natural killer receptor, providing insight into the biochemical nature of the gp42-HLA class II interaction.

Epstein-Barr virus is present in neoplastic cytotoxic T cells in extranodal, and predominantly in B cells in nodal T non-Hodgkin lymphomas

Epstein-Barr virus (EBV)-positive T non-Hodgkin lymphomas (T-NHLs) have been described, but it is at present unknown how EBV infects T lymphocytes. It has been postulated that cytotoxic T cells (CTLs) or natural killer (NK) cells can be infected by EBV during the killing of an EBV-infected target cell. The objective of this study was therefore to determine whether the neoplastic cells in EBV-positive T-NHLs (n=221) of various locations have a cytotoxic phenotype. To identify EBV-harbouring cells, combinations were used of EBV-encoded RNA (EBER) in situ hybridization (RISH) and immunohistochemistry for T- and B-cell markers and the cytotoxic proteins TIA-1 and granzyme B. EBV was detected in the neoplastic cells of all nasal T-NHLs (n=9), 5/34 gastrointestinal (GI) T-NHLs, and 2/6 lung T-NHLs, but not in primary cutaneous T-NHLs (n=103). Moreover, EBV was found in the neoplastic cells of 2/48 nodal anaplastic large cell lymphomas (ALCLs), but not in neoplastic T cells of other nodal T-NHLs. However, 5/17 nodal peripheral T-NHLs not otherwise specified (PTCLs NOS) and 1/4 T-prolymphocytic leukaemias did contain EBV-positive non-T cells. Double staining revealed that in EBV-positive extranodal T-NHLs (n=16), the EBER-positive cells had a cytotoxic phenotype (TIA-1- and/or granzyme B-positive). In nodal non-ALCL T-NHLs, the EBER-positive cells were not positive for TIA-1 or granzyme B, nor did they express CD3, CD21 or HECA452. Instead, most of these cells expressed the B-cell marker CD20. These PTCLs NOS with EBER-positive cells showed features of AILD-like T-NHL. It is concluded that neoplastic cells of EBV-positive extranodal T-NHLs always have a cytotoxic phenotype, supporting the view that EBV can infect CTLs. In nodal non-ALCL T-NHL, EBV is only found in T-NHL with AILD-like features and is present in B cells, where it may contribute to the outgrowth of a malignant B-cell clone.

Effect of interleukin-7 on the in vitro development and maturation of monocyte derived human dendritic cells

We have compared the cell phenotype and functional properties of monocyte/macrophage derived dendritic cells (DCs) obtained by culture of human adherent peripheral blood mononuclear cells (PBMCs) in medium containing granulocyte macrophage colony stimulating factor (GM-CSF) either alone (GM-CSF-DCs), or in combination with interleukin (IL)-4 (IL4-DCs) or IL-7 (IL7-DCs). The cell surface phenotype of GM-CSF-DCs and IL-7-DCs was characterized by a high expression of major histocompatibility complex (MHC) class I and II, CD80, CD86 and CD40. In contrast to 'classical' IL-4-DCs, these two types of DCs expressed CD14 and a CD21-like molecule detected by two out of four CD21-specific monoclonal antibodies (MoAb) tested. The same pattern of reactivity with CD21 specific antibodies was observed in freshly isolated adherent PBMCs but not in B lymphocytes. This reactivity was upregulated by IL-7 in a dose dependent manner. Lipopolysaccharide (LPS) treatment induced the upregulation of CD40, CD80, CD86 and the T-cell stimulatory capacity in IL-4-DCs and, to a lesser extent, in the IL-7-DCs whereas GM-CSF-DCs responded very poorly to such treatment. Our data indicate that, together with GM-CSF, the IL-7 drives macrophage precursors to a differentiation stage that is close to but distinct from the phenotype of IL-4-DCs. Comparison of DC development in the presence of IL-7 or IL-4 may help in dissecting signalling pathways that regulate the expression of functionally relevant DC markers.

Inactivation of NF-κB by EBV BZLF-1-Encoded ZEBRA Protein in Human T Cells

We have previously shown that the EBV ZEBRA protein (also denoted EB1, Z, or Zta) encoded by the BZLF open reading frame is expressed in primary human thymocytes and in human T lymphoblastoid cell lines infected by EBV. Expression of EBV-encoded gene products in T lymphocytes could contribute to viral pathogenesis during acute EBV infection as well as in individuals coinfected with EBV and HIV. HPB-ALL and Jurkat T lymphoblastoid cell lines transiently and stably expressing ZEBRA were characterized in this work. Expression of ZEBRA protein in human T lymphoblastoid cells was associated with decreased expression of an NF-κB reporter gene, altered expression of the NF-κB p50 protein subunit, and decreased DNA binding by components of NF-κB. These observations suggest that inactivation of NF-κB transcription by ZEBRA in EBV-infected T cells may be a novel mechanism of viral pathogenesis analogous in part to over-expression of the endogenous cytoplasmic inhibitor of NF-κB, IκBα.

EBV infection induced transformation of benign T lymphoproliferative state in patient with chronic active EBV infection into malignant lymphoma: implication of EBV infection as additive oncogenic factor in tumorigenesis

An 11-year-old girl with chronic EBV (Epstein-Barr virus) infection, who later developed malignant lymphoma in the lung, is reported. She had an increased number of V alpha2, V beta8, CD3, CD4, and HLADR positive activated lymphocytes (20-30% of total lymphocytes) in peripheral blood. One year later, she developed lymphoma in the lung, which was V alpha2, V beta8, CD3, CD4, HLADR and IL2Rbeta positive. At that time, the population in the peripheral blood increased up to 40%, but there was no evidence of lymphoma in the bone marrow. In situ hybridization revealed lymphoma cells were EBER-1 positive but gp350/220 and LMP mRNA negative. The EBV genome was detected in the tumor, but not in the peripheral T cells. Clonal analysis of the lymphoma cells revealed monoclonal rearrangement of the TcRbeta and gamma gene, however, investigation of the terminal repeat of EBV gene did not show the monoclonal pattern. These results indicate that infection of EBV into clonally activated T cells was related with transformation from benign lymphoproliferative disease to malignant lymphoma in this patient.

Biorecognition of HPMA copolymer-adriamycin conjugates by lymphocytes mediated by synthetic receptor binding epitopes

PURPOSE

The EDPGFFNVE nonapeptide (NP) was recognized as the CD21 (CR2) binding epitope of the Epstein-Barr virus (EBV) gp350/ 220 envelope glycoprotein which mediates the virus attachment to human B lymphocytes (Nemerow et al., Cell 56:369-377, 1989). Here we evaluated the targeting potential of a synthetic receptor binding epitope (NP) covalently attached to a water-soluble polymeric drug carrier. In particular, the biorecognition of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-NP conjugates by B- and T-cells and the cytotoxicity of HPMA copolymer-NP-adriamycin (ADR) conjugates toward B-cells, T-cells, and peripheral blood lymphocytes (PBL) were evaluated.

METHODS

HPMA copolymer-NP and optionally ADR conjugates varying in the NP density and mode of NP attachment were incubated with Raji B-cells (human Burkitt's lymphoma), CCRF-CEM T-cells (acute human lymphoblastic leukemia), and CCRF-HSB-2 T-cells (human lymphoblastic leukemia). The kinetics of binding was studied, the Langmuir adsorption isotherms analyzed, binding constants calculated, and IC50 doses determined.

RESULTS

Flow cytometry studies revealed that binding was homogeneous to both cell types. The apparent binding constants to T-cells were about two times higher when compared to B-cells. The binding and cytotoxicity increased with increased amount of epitopes per polymer chain. Attachment of the NP via a GFLG spacer resulted in increased biorecognition when compared with conjugates containing NP bound via a GG spacer. HPMA copolymer-NP-ADR conjugates possessed specific cytotoxicity to T- and B-malignant cells. Concentrations, which were lethal to the latter, were not toxic for PBL.

CONCLUSIONS

The data obtained seem to indicate the potential of the HPMA copolymer-NP conjugates as polymer anticancer drug carriers targetable to immunocompetent cells.

Analysis of Epstein-Barr virus (EBV) receptor CD21 on peripheral B lymphocytes of long-term EBV- adults

Primary infections with EBV are rarely observed after the age of 20. Some individuals even remain seronegative all their lives. Previously, a lack of EBV receptors on B cells of persistently EBV- adults was described as a reason for long-term EBV-seronegativity. The present study examined the CD21 receptor status of 20 repeatedly EBV- healthy adults and 32 EBV+ volunteers by means of flow cytometry. CD21 molecules on the surface of CD19+ B cells were quantified using anti-IgG-coated microbeads. The percentage of CD19+/CD21+ B lymphocytes was slightly lower in the peripheral blood of EBV- donors, but the CD21 antibody binding capacity on CD19+ B cells showed no significant differences between EBV- and EBV+ adults. In vitro studies showed an equally good EBV transformability of peripheral B lymphocytes of EBV- and EBV+ donors. Since HLA-DR was recently described as a co-receptor for EBV infection of B cells, we also determined HLA-DRB1 alleles in the EBV- group. We found a significant negative association of EBV-seronegativity with HLA-DR13 in comparison with 111 healthy blood donors. In summary, a biologically significant lack of the EBV receptor CD21 on peripheral B lymphocytes of persistently EBV- adults was excluded as a reason for long-term EBV-seronegativity.

Clonal change of infiltrating T-cells in children with familial hemophagocytic lymphohistiocytosis: possible association with Epstein-Barr virus infection

BACKGROUND

Although familial hemophagocytic lymphohistiocytosis (FHL) has been considered a T-cell disorder, to the authors' knowledge there are no previous reports on the clonal basis of FHL. In the current study the authors analyzed the clonality of T-cells in two FHL patients at the time of disease onset and at disease progression.

METHODS

Patient 1 had FHL and died of recurrent disease 4 months after bone marrow transplantation (BMT). His liver and spleen showed massive infiltrations of CD3+, CD4-, and CD8+ T-cells. The Epstein-Barr virus (EBV) genome was detected by in situ hybridization. Patient 2 also had FHL and died of progressive disease 9 weeks after the onset of disease despite chemotherapy. A polymerase chain reaction (PCR) analysis showed positive EBV genome in the peripheral blood, liver, and spleen of Patient 2. In the two patients, T-cell receptor-beta and alpha-chain variable region (TCR Vbeta and V alpha) repertoires in peripheral mononuclear cells were analyzed at the time of disease onset and at disease progression by the inverse PCR method. When a high usage (> 15%) of a specific Vbeta family member was observed, a clonal analysis was performed by PCR using beta-chain joining region (Jbeta) primers. The clonality of specific Vbeta-Jbeta fragments was confirmed by a single strand confirmation polymorphism (SSCP) analysis.

RESULTS

Although there was no preferential usage of Vbeta in Patient 1, the exclusive expression of Jbeta1.2 for Vbeta13 was observed. A high frequency of Vbeta13 also was observed at the time of disease progression, but the Jbeta fragment for Vbeta13 was polyclonal. In Patient 2, the restricted usage of Jbeta1.6 for Vbeta5a was observed at the time of disease onset, whereas Jbeta1.1 and 1.2 for Vbeta4 were observed exclusively at the time of disease progression. The clonality of Vbeta13-Jbeta1.2 in Patient 1 and Vbeta5a-Jbeta1.6 and Vbeta4-Jbeta1.1/Jbeta1.2 in Patient 2 was confirmed by SSCP analysis.

CONCLUSIONS

These findings suggest that the polyclonal T-cell lymphoproliferative disease associated with EBV was induced after BMT in Patient 1, and that the clonal change of expanded T-cells also was induced by EBV in Patient 2. The clonal analysis of T-cells is a useful tool to clarify the pathogenesis of FHL.

Detection of Epstein-Barr virus in Korean peripheral T-cell lymphoma

One hundred thirty-seven patients with peripheral T-cell lymphomas (PTL) were examined for the presence of Epstein-Barr virus (EBV) using in situ hybridization for EBV-encoded RNA (EBER) and Bam H-fragment, lower strand frame (BHLF) and immunohistochemical stain for latent membrane protein (LMP). EBER was detected in tumor cells in 79 cases (58%); 26/66 PTL, unspecified (39%), 3/4 AILD (75%), 47/51 angiocentric lymphomas (AL) (92%), and 3/13 anaplastic large cell lymphoma (ALCL) (23%) by Revised European-American Lymphoma (REAL) classification. EBER was detected in 17/36 nodal (47%) vs. 62/101 extranodal PTLs (61%); 21/24 nasal, 12/32 Waldeyer's ring, 9/13 gastrointestinal, and 20/32 skin and soft tissue PTL. AL was consistently associated with the highest frequency of EBER among the extranodal PTL: nose (19/20), GI tracts (3/3), skin (14/15), and Waldeyer's ring (11/14). In extranodal lymphomas, coagulative-type zonal necrosis was seen almost exclusively in AL and showed correlation with EBER-positivity (P < 0.01). LMP was detected in 24 among 107 cases tested (22%). No signal for BHLF was detected in 76 cases tested, implying absent or negligible incidence of lytic infection. In conclusion, high incidence of EBV was observed in PTL among Koreans, with predilection for angiocentric lymphomas and extranodal presentation, especially involving nose, skin, and gastrointestinal tract.

Atypical CD3+ CD4(low) cell population in a boy with fatal EBV-infection

A previously healthy 10-year-old Greek boy born to nonconsanguineous healthy parents developed progressive liver disease after acute infectious mononucleosis. EBV-induced autoimmune hepatitis was suspected and treatment was started with high-dose prednisolone, acyclovir and intravenous immunoglobulins. Despite therapy, his liver function continuously deteriorated and the child died 9 months later in profound immune deficiency from candida septicemia. Flow cytometric analysis of his lymphocytes revealed a major subpopulation of atypical cells (20.3%) which were CD3+, fitted into the lymphocyte gate but showed a very low level of CD4 expression, comparable to that of monocytes. After short-time cell culture, the cells became adherent and developed granules and dendrites. We conclude that these cells may represent strongly activated CD4+ T lymphocytes with downregulated CD4 expression or a subtype of dendritic cells.

Complement receptor 2 in the regulation of the immune response

Antigens coated with split products of C3, the result of complement activation, are capable of crosslinking the complement receptor 2 (CR2, CD21) and the antigen receptor on the surface of B cells simultaneously. This dual recognition leads to increased cell proliferation and differentiation and enhanced antibody production. CR2 is also considered to be a regulator of the B cell response to antigen. In this review we summarize the biology of the CR2 and focus on its essential role in generating an effective B cell response to antigenic stimuli. The involvement of CR2 in the pathophysiology of infectious and autoimmune diseases is also discussed.

Epstein-Barr Virus Infects and Induces Apoptosis in Human Neutrophils

The role of neutrophils during Epstein-Barr virus (EBV) infection is not known. Disruption of the initial and nonspecific immune response may favor the spread of EBV infection. We have previously shown that EBV interacts with human neutrophils and modulates protein expression. In this study we have investigated the ability of EBV to infect neutrophils. Electron microscopy studies showed penetration of virus and its subsequent localization to the nucleus. The presence of viral genomes in isolated nuclei from neutrophils was also shown by polymerase chain reaction (PCR). Expression of viral transcripts like EBNA-2 (Epstein-Barr nuclear antigen-2) and ZEBRA (BamHI Z EBV replication activator) was not detected by reverse transcriptase (RT)-PCR, suggesting that EBV does not seem to establish a latent or a lytic infection in neutrophils. However, at 20 hours post-EBV infection, 77% of cells were apoptotic as compared to 22% in uninfected cell cultures, as evaluated by flow cytometry. This EBV-induced apoptosis was prevented by the addition of granulocyte-macrophage colony-stimulating factor to the cell cultures. Apoptotic cell death seems to implicate the Fas/Fas ligand (L) pathway, as reflected by an increase of Fas/Fas L expression on neutrophils treated with EBV and an increase of soluble Fas L, which may function in an autocrine/paracrine pathway to mediate cell death. Lastly, EBV genome was detected from neutrophils of infectious mononucleosis (IM) patients in contrast to neutrophils obtained from healthy EBV-seropositive donors. Our findings on the interactions of EBV with neutrophils will then provide new insights on the immunosuppressive effects associated with EBV infection.

Primary intestinal non-Hodgkin's lymphoma and Epstein-Barr virus: high frequency of EBV-infection in T-cell lymphomas of Mexican origin

Epstein-Barr virus is universally associated with endemic Burkitt's lymphoma (BL) and undifferentiated nasopharyngeal carcinoma and can be detected in a significant proportion of cases of Hodgkin's disease (HD) and peripheral T-cell lymphoma, but only rarely in sporadic B-NHL. The frequency of EBV-positivity in certain neoplasms shows important geographic variations. Both HD and sporadic BL from Latin America have shown higher rates of EBV-association than cases from Western countries. In T-NHL, the frequency of EBV-positivity is influenced by the site of the primary tumor and the phenotype of the neoplastic cells. Nasal and nasal-type T-NHL, which show a T/NK-cell phenotype with expression of CD56 are virtually always EBV-associated, whereas only a proportion of nodal, gastrointestinal and pulmonary T-NHL are EBV-infected. A recent investigation of primary intestinal lymphomas of Mexican origin demonstrated EBV-positivity in all examined cases of T-NHL and BL and a proportion of other B-NHLs. The presence of EBV was independent of the presence or absence of enteropathy. Two of 6 cases studied showed CD56 expression. The high rate of EBV-positivity independent of histologic subtype is in contrast to the low to intermediate rates of EBV-positivity found in cases of intestinal T-NHL from Western countries and indicates that geographic differences in the frequency of EBV-association of lymphoid neoplasms might also extend to a fraction of peripheral T-cell lymphomas.

Epstein-Barr virus infections and their association with human malignancies: some key questions

Epstein-Barr virus (EBV) expresses genes that stimulate cells to divide in culture. This property, coupled with the close association of the virus with numerous malignancies, has prompted its designation as a human DNA tumour virus. Before human herpesvirus 8 (HHV-8, alternatively KS virus) was discovered, EBV was unique in this property among the human herpesviruses. EBV infection has been best characterised in terms of gene expression in B lymphocytes and epithelium, which represent cells found in the best known of the associated malignancies, Burkitt's lymphoma and poorly differentiated nasopharyngeal carcinoma. The bulk of evidence supports B cells as the primary EBV reservoir with the viral route into other cell types remaining ill-defined. Molecular studies on gene expression in the associated tumours suggest that EBV encodes a number of functions associated with cell growth; whether they are expressed or silent may largely be under control of the host cell. Many questions partly addressed here remain with regard to this virus, two critical ones relating to the mechanisms by which viral gene products escape T-cell recognition - relevant from the fact that gene expression is not tightly restricted to nonimmunogenic functions in tumours - and whether EBV can invoke cell growth in a manner not requiring its continued presence. The latter seems a plausible hypothesis and is of particular importance with regard to identifying and understanding pathologies associated with EBV, as viral transcriptional transactivators may on initial infection permanently perturb cell regulation.

Structure, functions, and evolution of the third complement component and viral molecular mimicry

The third component of the complement system, C3, is a common denominator in the activation of the classical, alternative, and lectin pathways. The ability of C3 molecule to interact with at least 20 different proteins makes it the most versatile component of this system. Since these interactions are important for phagocytic, immunoregulatory, and immune evasion mechanisms, the analysis of its structure and functions has been a subject of intense research. Here we review our current work on the C3-ligand interactions, C3-related viral molecular mimicry, evolution of the complement system, and identification of C3-based complement inhibitors.

Upregulation of tumor necrosis factor-alpha gene by Epstein-Barr virus and activation of macrophages in Epstein-Barr virus-infected T cells in the pathogenesis of hemophagocytic syndrome

A potentially fatal hemophagocytic syndrome has been noted in patients with malignant lymphomas, particularly in EBV-infected T cell lymphoma. Cytokines, such as interferon-gamma (IFN-gamma), TNF-alpha, and IL-1alpha, are elevated in patients' sera. To verify whether infection of T cells by EBV will upregulate specific cytokine genes and subsequently activate macrophages leading to hemophagocytic syndrome, we studied the transcripts of TNF-alpha, IFN-gamma, and IL-1alpha in EBV-infected and EBV-negative lymphoma tissues. By reverse transcription PCR analysis, transcripts of TNF-alpha were detected in 8 (57%) of 14 EBV-infected T cell lymphomas, higher than that detected in EBV-negative T cell lymphoma (one of six, 17%), EBV-positive B cell lymphoma (two of five, 40%) and EBV-negative B cell lymphomas (one of seven, 14%). Transcripts of IFN-gamma were consistently detected in T cell lymphoma and occasionally in B cell lymphoma, but were independent of EBV status. IL-1alpha expression was not detectable in any category. Consistent with these in vivo observations, in vitro EBV infection of T cell lymphoma lines caused upregulation of TNF-alpha gene, and increased secretion of TNF-alpha, but not IFN-gamma or IL-1alpha. Expression of TNF-alpha, IFN-gamma, and IL-1alpha was not changed by EBV infection of B cell lymphoma lines. To identify the specific cytokine(s) responsible for macrophage activation, culture supernatants from EBV-infected T cells were cocultured with a monocytic cell line U937 for 24 h. Enhanced phagocytosis and secretion of TNF-alpha, IFN-gamma, and IL-1alpha by U937 cells were observed, and could be inhibited to a large extent by anti-TNF-alpha (70%), less effectively by anti-IFN-gamma (31%), but almost completely by the combination of anti-TNF-alpha and anti-IFN-gamma (85%). Taken together, the in vivo and in vitro observations suggest that infection of T cells by EBV selectively upregulates the TNF-alpha expression which, in combination with IFN-gamma and probably other cytokines, can activate macrophages. This study not only highlights a probable pathogenesis for virus-associated hemophagocytic syndrome, but also suggests that anti-TNF-alpha will have therapeutic potential in the context of their fatal syndrome.

Pathways controlling the expression of surface CD21 (CR2) and CD23 (Fc(epsilon)IIR) proteins in human malignant B cells

The aim of the present study was to analyze the pathways regulating the expression of CD21 and CD23 B-cell differentiation antigens on human malignant B cells. Exposure of Farage cells, derived from a human B-cell lymphoma, to phorbol 12-myristate 13-acetate (PMA) down-regulated CD21 and CD23 expression, while interleukin 4 (IL4) inhibited the expression of CD21 but augmented CD23 expression. When Farage cells were stained with either anti-CD21 or anti-CD23 monoclonal antibodies (mAb), subsequent exposure to IL4 failed to change the staining of the cells, indicating that IL4 did not affect the turnover of CD21 and CD23 molecules. Inhibition of protein synthesis with cycloheximide (CXM) had no effect on the expression of CD21 molecules, but abrogated their down-regulation by IL4, suggesting that IL4 induced the synthesis of proteins which modify the processing of CD21 molecules. The inhibitory effect of IL4 on the expression of CD21 and its augmentary effect on the expression of CD23 was abrogated by H7 (1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine), an inhibitor of serine protein kinase. Staurosporine, an additional inhibitor of serine kinases also abrogated the effect of IL4 on CD23 expression. H8 (N-(2-[Methylamino]ethyl)-5-isoquinolinesulfonamide), a preferential inhibitor of protein kinases A and G, and genistein, an inhibitor of tyrosine kinases had no effect on IL4-induced modulation of CD21 and CD23 in Farage cells. The exposure of B-chronic lymphocytic leukemia (CLL) cells to PMA reduced the expression of CD21, but increased the expression of CD23. IL4 had no effect on the expression of CD21 on CLL-cells but strongly enhanced the level of CD23. H7, H8 and genistein each abrogated to a different extent the effect of IL4 on the expression of CD23 by CLL-cells. These data indicate that activation of serine/threonine kinases in malignant B cells inhibited the production of CD21 proteins, while different protein kinases appeared to be involved in up- and down-regulation of CD23 in different B lymphocytes.

Synergy between human immunodeficiency virus type 1 and Epstein-Barr virus in T lymphoblastoid cell lines

CR2 (CD21), the EBV receptor, was detected on three of four CD4-positive cell lines by indirect fluorescent labeling, and its corresponding mRNA was found by use of the reverse transcription-based polymerase chain reaction. To determine whether CR2 on CD4-positive cells was functional, their ability to be infected by EBV was analyzed. EBV DNA, EBV nuclear antigen 2 (EBNA-2A), and EBV-encoded small RNA (EBER1) transcripts could be detected in CR2-expressing CD4-positive cells following infection by the B95.8 strain of EBV. Analysis of the terminal region showed the EBV genome remained linear following infection, and copy number decreased with time. Since CD4-positive cell lines are targets for HIV-1 infection, the effects of EBV infection on HIV-1 expression were analyzed. HIV-1 replication was upregulated when CD4-positive cells were coinfected with EBV strain B95.8 but not P3HR-1K. These results suggested that EBNA-2 is involved in upregulation of HIV-1 expression in T lymphoblastoid cell lines. To test this hypothesis an EBNA-2-expression vector was transfected into T lymphoblastoid cell lines and HIV-1 expression measured. First, trans-activation of HIV-1 long terminal repeat (LTR) by Tat was enhanced by EBNA-2 type 1 expression. trans-Activation of the HIV-1 LTR by Tat was also enhanced when CD4-positive cells were infected by EBV (strain B95.8) encoding an intact EBNA-2, but not by P3HR-1K with a deleted EBNA-2. In addition, CD4-positive cell clones stably expressing EBNA-2 supported enhanced HIV-1 replication as measured by accumulation of reverse transcriptase activity and syncytium induction. This provides direct evidence that EBV infection can enhance HIV-1 replication in T cells. Whether this in vitro phenomenon contributes to disease progression in vivo remains to be determined.

Primary Non-Hodgkin's Lymphoma of the Intestine: High Prevalence of Epstein-Barr Virus in Mexican Lymphomas as Compared With European Cases

Recent studies in Western European populations have shown that peripheral T-cell non-Hodgkin's lymphomas (T-NHLs) are associated with Epstein-Barr virus (EBV) in a higher percentage than sporadic B-cell NHL (B-NHLs), and that the frequency of EBV-positivity might be influenced by the primary site of the tumor. Because of the geographic differences in EBV expression in Burkitt's lymphoma (BL) and Hodgkin's disease (HD), and the lack of studies of sporadic NHL from developing countries, we decided to survey the presence of EBV in a series of primary intestinal lymphomas from patients in Mexico and in Western Europe, and to analyze whether EBV status is influenced by tumor phenotype, and geographic or ethnic determinants. Paraffin-embedded tissue from 43 primary intestinal NHLs (19 cases from Mexico and 24 from Western Europe) were examined, including 17 high grade B-NHLs, 9 low grade B-NHLs, and 17 T-NHLs; 6 of which were enteropathy associated T-cell lymphomas. The distribution of histologic subtypes was similar in both groups. The presence of EBV was investigated with a combined approach using a nested polymerase chain reaction technique as well as immunohistochemistry for latent membrane protein-1 and in situ hybridization for EBV early RNA transcripts (EBER 1/2) RNAs. The median age of the Mexican patients was significantly lower than the median age of the European patients (32 v 62 years). This difference was most pronounced in patients with T-cell lymphoma (24 v 63 years). EBER-positive tumor cells were detected in 13 of the 43 (30%) cases of primary intestinal lymphoma, including 5 of 26 sporadic B-NHL (3 high grade and 2 low grade), and 8 of 17 T-NHL, all of which were classified as pleomorphic, medium and large cell. The rates of EBV-positivity were markedly different for European and Mexican cases. Whereas 7 of 7 (100%) T-NHL and 5 of 12 (42%) sporadic B-NHL of Mexican origin were EBER-positive, only 1 of 10 T-NHL and 0 of 14 sporadic B-NHL from Europe showed EBER expression in tumor cells. Latent membrane protein was positive in only 2 of 43 cases, 1 of which was an EBER-negative high grade B-NHL from Mexico that showed intact total mRNA in control hybridization. CD30 expression was found in 4 of 8 EBV-positive T-NHL and in none of the EBV-positive B-NHL. In contrast to European cases, intestinal NHLs from Mexico show a very high frequency of EBV-positivity, which is not limited to T-NHL, but includes a significant proportion of B-NHL. This study strongly suggests that similar to HD and probably BL, there are important epidemiologic differences in EBV association in intestinal T-cell NHL between European and Mexican populations. These differences might be the result of environmental factors, for example, earlier contact with childhood viruses on intestinal lymphomagenesis.

Infection of primary CD4+ and CD8+ T lymphocytes by Epstein-Barr virus enhances human immunodeficiency virus expression

CD4+ and CD8+ T lymphocytes purified from normal adult donors by flow cytometry could be infected with Epstein-Barr virus (EBV) as measured by the accumulation of components of the EBV replicative cycle, viral DNA and viral transcripts encoding EBER1 and BRLF1. EBV infection resulted in enhanced replication of human immunodeficiency virus type 1 (HIV-1) IIIB in CD4+ lymphocytes as measured by accumulation of reverse transcriptase and formation of syncytia. Furthermore, a small percentage of CD8+ T cells became permissive after infection with EBV. Inactivation of transforming functions by irradiation with UV light greatly reduced the ability of EBV to enhance HIV-1 replication in T4+ T cell, suggesting that live virus is needed for enhancement. These results demonstrate a direct synergy between EBV and HIV-1 during coinfection of T cells in vitro and may explain the beneficial effect of acyclovir in combination with antiretroviral chemotherapy as well as the increased incidence of T-cell lymphomas associated with EBV in patients with AIDS.