A20/TNFAIP3 inhibits NF-κB activation induced by the Kaposi's sarcoma-associated herpesvirus vFLIP oncoprotein

Kaposi's sarcoma-associated herpesvirus (KSHV) K13/vFLIP (viral Flice-inhibitory protein) induces transcription of numerous genes through NF-κB activation, including pro-inflammatory cytokines, which contribute to the pathogenesis of Kaposi's sarcoma (KS). In this study, we report that KSHV vFLIP induces the expression of the NF-κB regulatory proteins A20, ABIN-1 and ABIN-3 (A20-binding NF-κB inhibitors) in primary human endothelial cells, and that KS spindle cells express A20 in KS tissue. In reporter assays, A20 strongly impaired vFLIP-induced NF-κB activation in 293T cells, but ABIN-1 and ABIN-3 did not. Mutational analysis established that the C-terminal domain (residues 427-790) is critical for A20 modulation of NF-κB, but the ubiquitin-editing OTU (ovarian tumor) domain is not. In functional assays, A20 inhibited vFLIP-induced expression of the chemokine IP-10, reduced vFLIP-induced cell proliferation and increased IKK1 protein levels. Thus, we demonstrate that A20 negatively regulates NF-κB activation directly induced by KSHV vFLIP. By attenuating excessive and prolonged vFLIP-induced NF-κB activation that could be harmful to KSHV-infected cells, A20 likely has an important role in the pathogenesis of KSHV-associated diseases, in which vFLIP is expressed.

Measurement of polyclonal immunoglobulin synthesis using the reverse plaque technique

This unit describes the reverse hemolytic plaque assay, an effective method for measuring the number of immunoglobulin (Ig)-secreting cells present in a cell population at any particular time. Cell populations that can be assayed using the technique include peripheral blood mononuclear cells or cells from tissues such as the tonsils. The basic protocol is divided into three stages. First, protein A-sensitized sheep red blood cells (SRBC), guinea pig complement, and anti-Ig antibody are prepared. Test samples are then combined and incubated with the SRBC, complement, and antibody in appropriate chambers. Finally, the resulting plaques are scored. A support protocol describes the preparation of plaquing chambers.

Interactions between HIV-1 Tat and KSHV

Since the advent of the HIV-1 pandemic, a close association between HIV-1 infection and the development of selected types of cancers has been brought to light. The discovery of Kaposi sarcoma-associated herpesvirus (KSHV) has led to significant advances in uncovering the virological and molecular mechanisms involved in the pathogenesis of AIDS-related malignancies. Extensive evidence indicates that HIV-1 trans-activating protein Tat plays an oncogenic role in the development of KSHV-associated neoplasms. Comprehensive knowledge of the functions of Tat-1 together with the KSHV genes will contribute to a better understanding of the pathogenesis of virus-associated cancers and the interaction of viruses with their hosts.

Macrophage-derived chemokine expression in classical Hodgkin's lymphoma: application of tissue microarrays

Hodgkin's disease (HD) is a lymphoid malignancy characterized by the presence of Reed-Sternberg (RS) and Hodgkin's cells in a background of mixed inflammatory cells and stromal reaction. Studies have documented that HD is a neoplasm associated with abnormal cytokine and chemokine production. To define the expression of macrophage-derived chemokine (MDC) in HD, 57 cases (18 lymphocyte predominant, 11 mixed cellularity, 28 nodular sclerosis) were stained for MDC by immunohistochemistry and compared with reactive lymph nodes as controls. MDC was expressed by RS cells in classical HD (CHD) and showed a distinct cytoplasmic and Golgi localization. Accumulating evidence suggests that lymphocyte-predominant HD (LPHD) represents an entity distinct from CHD, with different biological properties and clinical course. On the basis of the high level of MDC staining alone, CHD could be distinguished from LPHD (P <.001), which showed only faint staining of scattered histiocytes similar to control tissues. CHD cases with high MDC mRNA levels showed high levels of MDC protein expression by immunohistochemistry (P <.001) and significant eosinophil infiltration, suggesting that MDC may represent another molecule that plays a critical role in eosinophil recruitment. We also analyzed 102 cases of non-Hodgkin's lymphoma and normal spleen, lymph node, and thymic tissue. High levels of MDC expression were specific to CHD cases because only low levels of MDC were observed in a minor subset of LPHD, NHL or normal lymphoid tissues.

Receptor engagement by viral interleukin-6 encoded by Kaposi sarcoma-associated herpesvirus

Receptor usage by viral interleukin-6 (vIL-6), a virokine encoded by Kaposi sarcoma- associated herpesvirus, is an issue of controversy. Recently, the crystal structure of vIL-6 identified vIL-6 sites II and III as directly binding to glycoprotein (gp)130, the common signal transducer for the IL-6 family of cytokines. Site I of vIL-6, however, comprising the outward helical face of vIL-6, where human IL-6 (hIL-6) would interact with the specific alpha-chain IL-6 receptor (IL-6R), is accessible and not occupied by gp130. This study examined whether this unused vIL-6 surface is available for IL-6R binding. By enzyme-linked immunosorbent assay, vIL-6 bound to soluble gp130 (sgp130) but not to soluble IL-6R (sIL-6R). Using plasmon surface resonance, vIL-6 bound to sgp130 with a dissociation constant of 2.5 microM, corresponding to 1000-fold lower affinity than that of hIL-6/sIL-6R complex for gp130. sIL-6R neither bound to vIL-6 nor affected vIL-6 binding to gp130. In bioassays, vIL-6 activity was neutralized by 4 monoclonal antibodies (mAbs) recognizing a domain within vIL-6 site I, mapped to the C-terminal part of the AB-loop and the beginning of helix B. The homologous region in hIL-6 participates in site I binding to IL-6R. In addition, binding of vIL-6 to sgp130 was interfered with specifically by the 4 neutralizing anti-vIL-6 mAbs. Based on the vIL-6 crystal structure, the vIL-6 neutralizing mAbs map outside the binding interface to gp130, suggesting that they either produce allosteric changes or block necessary conformational changes in vIL-6 preceding its binding to gp130. These results document that vIL-6 does not bind IL-6R and suggest that conformational change may be critical to vIL-6 function.

The angiogenesis inhibitor vasostatin does not impair wound healing at tumor-inhibiting doses

Inhibition of tumor angiogenesis represents a promising new approach for the treatment of human cancers. It has remained unclear, however, whether inhibition of tumor angiogenesis may also result in impaired wound healing, a process thought to be angiogenesis dependent. To determine the effects of the angiogenesis inhibitor vasostatin, a 180 amino acid calreticulin fragment, on wound healing at tumor inhibiting doses, full-thickness wounds were generated on the back of nude mice that were also injected intradermally with CA46 Burkitt lymphoma cells. Mice were treated with daily injections of vasostatin or vehicle control at a site between the wounds and the transplanted tumor cells over 14 d. Vasostatin potently inhibited tumor growth and significantly reduced tumor angiogenesis, as measured by computer-assisted image analysis of CD31-stained tumor sections. Moreover, vasostatin treatment resulted in an increased fraction of mature tumor-associated blood vessels. In contrast, no impairment of wound healing was observed in vasostatin-treated mice, despite a significantly reduced vascularity of the wound granulation tissue. Our results reveal a different sensitivity of malignant tumor growth and physiologic wound healing to inhibition of angiogenesis, and they suggest that therapeutic inhibition of tumor angiogenesis may be achieved without impairment of tissue repair.

Chemokine gene expression and clonal analysis of B cells in tissues involved by lymphoid interstitial pneumonitis from HIV-infected pediatric patients

Lymphoid interstitial pneumonitis (LIP), a frequent pulmonary complication in HIV-infected pediatric patients, is characterized histologically by marked infiltration of lymphoid cells. We sought to evaluate the nature and pathogenesis of the lymphoid infiltrates and to examine the relationship of LIP to pulmonary MALT lymphoma that has been described in pediatric HIV positive patients. To examine the potential contribution of chemokines and cytokines to the inflammatory cell recruitment in tissues involved by lymphoid interstitial pneumonitis from HIV-infected pediatric patients, RNA was extracted from paraffin-embedded tissues from five lung biopsies in four pediatric HIV-positive patients and from five control, normal lung biopsies in five HIV-negative patients and was analyzed by semiquantitative RT-PCR for the expression of cytokines (TNF-alpha, GM-CSF, IFN-gamma, IL-4, IL-6, IL-10, and IL-18) and chemokines (IP-10, Mig, regulated upon activation, normal T expressed and secreted [RANTES], and MIP1-alpha and beta) after normalization for G3PDH. Expression of IL-18 was increased, as well as expression of IFN-gamma-inducible chemokines IP-10 and Mig in LIP tissues compared with controls. RANTES and MIP1-alpha and -beta were also increased in pediatric LIP lesions compared with controls. In contrast, expression of TNF-alpha, GM-CSF, IL-10, and IL-6 was variable in LIP tissues and controls. In addition, clonality of the B-cell population was evaluated by VDJ-PCR. A polyclonal B-cell population was shown in all five biopsies from five patients with LIP; and in one patient with concurrent LIP and MALT lymphoma, a band of increased intensity was observed in the LIP biopsy that was identical in size to the monoclonal band in the concurrent MALT lymphoma biopsy. These results provide evidence of high-level expression of certain chemokines in lymphoid interstitial pneumonitis tissues and suggest that chemokines and cytokines may play an important role in the recruitment of inflammatory cell infiltrates into these tissues. In addition, LIP may represent an early stage of MALT lymphoma or an immunologic response to a chronic antigenic stimulus that may provide a milieu or microenvironment for the evolution of a monoclonal B-cell population.

Diagnosis of atypical cases of infectious mononucleosis

The variable manifestations of infectious mononucleosis rarely cause clinicians to suspect primary Epstein-Barr virus or cytomegalovirus infection; consequently, costly diagnostic tests and unnecessary treatments are undertaken. Seventeen cases of clinically atypical and 11 cases of clinically typical infectious mononucleosis were diagnosed through screening for atypical and apoptotic lymphocytes in the peripheral blood samples by means of an automated hematologic analyzer. Atypical and typical cases did not differ significantly with respect to peripheral white blood cell counts; percentages of lymphocytes, atypical lymphocytes, CD4(+) lymphocytes, human leukocyte antigen--DR positivity in CD3 lymphocytes, or apoptotic cells in blood smear after incubation; or levels of aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase. Only the percentage of CD8(+) lymphocytes was significantly higher in patients with typical infectious mononucleosis than it was in patients with atypical infectious mononucleosis. Because certain atypical cases of infectious mononucleosis display laboratory abnormalities that are characteristic of typical infectious mononucleosis, enhanced awareness can help in the diagnosis.

Hypoxia induces lytic replication of Kaposi sarcoma-associated herpesvirus

There is substantial evidence that Kaposi sarcoma-associated herpesvirus (KSHV) plays an important role in the pathogenesis of all forms of Kaposi sarcoma (KS). It has been noted that KS commonly occurs in locations, such as the feet, where tissue may be poorly oxygenated. On the basis of this observation, the potential role of hypoxia in the reactivation of KSHV replication was explored by studying 2 KSHV-infected primary effusion lymphoma B-cell lines (BC-3 and BCBL-1) latently infected with KSHV. Acute and chronic exposure of these cells to hypoxia (1% O(2)) induced KSHV lytic replication, as indicated by an increase in intracellular lytic protein expression and detection of virus in cell supernatants by Western immunoblotting. In addition, hypoxia increased the levels of secreted viral interleukin-6. Moreover, hypoxia enhanced the lytic replication initiated by the viral inducer 12-O-tetradecanoylphorbol-13-acetate. Desferoxamine and cobalt chloride, 2 compounds that increase the intracellular levels of hypoxia-inducible factor 1, were also able to induce KSHV lytic replication. These studies suggest that hypoxia is an inducer of KSHV replication. This process may play an important role in the pathogenesis of KS.

Interleukin-18 expression induced by Epstein-Barr virus-infected cells

Human Epstein-Barr virus (EBV)-negative Burkitt lymphomas cells usually grow as malignant subcutaneous tumors in athymic mice, but these tumors regress when the Burkitt cells are injected in conjunction with EBV-positive lymphoblastoid cells or when the Burkitt cells are transfected with the EBV latent membrane protein-1 (LMP-1) gene. Tumor regression is mediated, in part, by murine interferon gamma (IFN-gamma) and the IFN-gamma-induced murine chemokine IFN-gamma-inducible protein-10 (IP-10). The mechanisms by which EBV-LMP-1 promotes the expression of IFN-gamma has remained unclear. Here we show that murine interleukin (IL)-18 was consistently expressed in regressing Burkitt tumors but was either expressed at low levels or absent from progressively growing Burkitt tumors. By immunohistochemical methods, IL-18 protein was visualized in regressing but not in progressively growing Burkitt tumors. In contrast, IL-12 p35 and IL-12 p40 were only rarely expressed in regressing Burkitt tumors. In splenocyte cultures, EBV-infected lymphoblastoid cells and LMP-1-transfected Burkitt cells promoted the expression of IL-18 but not the expression of IL-12 p35 and IL-12 p40. A neutralizing antibody directed at murine IL-18 reduced murine IP-10 expression induced by EBV-immortalized cells in splenocyte cultures. These results provide evidence for IL-18 expression in response to a viral latency protein and suggest that IL-18 may play an important role as an endogenous inducer of IFN-gamma expression, thereby contributing to tumor regression.

Detection of viral interleukin-6 in Kaposi sarcoma-associated herpesvirus-linked disorders

Expression of a viral interleukin-6 (vIL-6) has been detected in certain Kaposi sarcoma (KS)--associated herpesvirus positive (KSHV(+)) lesions. The release of vIL-6 systemically and its contribution to the pathogenesis of HIV-related malignancies was studied. Serum vIL-6 was detected in 13 (38.2%) of 34 HIV(+) patients with KS, in 6 (85.7%) of 7 HIV(+) patients with primary effusion lymphoma (PEL) and/or multicentric Castleman disease (MCD), and in 18 (60.0%) of 30 HIV(+), mostly homosexual, individuals without KS, MCD, or PEL. By contrast, serum vIL-6 was detected in only 3 (23.1%) of 13 patients with classic KS, 1 (2.5%) of 40 blood donors from the United States, and 4 (19.0%) of 21 blood donors from Italy. Circulating vIL-6 levels were associated with HIV(+) status (P <.0001). However, within the HIV(+) cohort, serum vIL-6 levels were not associated with the occurrence of KSHV-associated malignancies (P =.43). (Blood. 2001;97:2173-2176)

Vascular endothelial growth factor/vascular permeability factor in the pathogenesis of primary effusion lymphomas

Primary effusion lymphomas (PEL), rare lymphomas associated with Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8) infection, present as malignant lymphomatous effusions in body cavities. We have recently found that PEL effusions contain high levels of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). VEGF/VPF, an important regulator of tumor-angiogenesis in vivo, exerts its effects acting through the receptors KDR/Flk-1 and Flt-1 on the endothelial cell membrane. In vitro, the PEL cell lines BC-1, BCP-1 and BCBL-1 produce high levels of VEGF. RT-PCR analysis of RNA from the PEL cell lines amplified the three VEGF/VPF secreted isoforms, VEGF/VPF(121), VEGF/VPF(145) and VEGF/VPF(165). Two of the PEL cell lines express the VEGF/VPF receptor Flt-1, but VEGF did not stimulate proliferation in these cells. SCID/beige mice inoculated intraperitoneally with BCBL-1 cells developed effusion lymphoma of human cell origin with prominent bloody ascites. In contrast, none of the mice treated with a neutralizing anti-human VEGF/VPF antibody developed ascites and effusion lymphoma. Although the precise mechanisms by which VEGF/VPF can promote vascular permeability are not fully understood, VEGF/VPF stimulation of vascular leakage may be critical to the pathogenesis of PEL.

Effective targeting of tumor vasculature by the angiogenesis inhibitors vasostatin and interleukin-12

Solid tumors are dependent on preexisting vasculature and neovascularization for their growth. Successful cancer therapies targeting the tumor vasculature would be expected to block the existing tumor blood supply and to prevent tumor neovascularization. We tested the antitumor activity of experimental therapy with 2 distinct antiangiogenic drugs. Vasostatin inhibits endothelial cell growth and neovascularization, and interleukin-12 (IL-12) targets the tumor vasculature acting through interferon-gamma (IFN-gamma) and the downstream chemokines interferon-inducible protein-10 (IP-10) and monokine induced by IFN-gamma. Individually, vasostatin and IL-12 produced distinct efficacy profiles in trials aimed at reducing tumor growth in athymic mice. In combination, these inhibitors halted the growth of human Burkitt lymphoma, colon carcinoma, and ovarian carcinoma. Thus, cancer therapy that combines distinct inhibitors of angiogenesis is a novel, effective strategy for the experimental treatment of cancer. (Blood. 2000;96:1900-1905)

Viral and cellular cytokines in AIDS-related malignant lymphomatous effusions

Kaposi sarcoma-associated herpesvirus encodes viral IL-6 (vIL-6). To investigate the potential role of vIL-6 in the pathogenesis of human immunodeficiency virus (HIV)- related primary effusion lymphomas (PEL), a sensitive enzyme-linked immunosorbent assay was developed for vIL-6 and applied to the study of PEL. Whereas vIL-6 was detectable in 6 of 8 PEL effusions (range, 1390-66 630 pg/mL), it was not detectable in any of the control effusions. As expected, all PEL effusions contained human IL-6 (range, 957-37 494 pg/mL), and 7 of 8 contained detectable human IL-10 (range, 66-2,521,297 pg/mL). Human and vIL-6 have previously been shown to induce vascular endothelial growth factor, which in turn can increase vascular permeability. The results of the current study suggest that these cytokines play a central role in the pathogenesis and manifestations of PEL. (Blood. 2000;96:1599-1601)

Activity of thalidomide in AIDS-related Kaposi's sarcoma

PURPOSE

To assess the toxicity and activity of oral thalidomide in Kaposi's sarcoma (KS) in a phase II dose-escalation study.

PATIENTS AND METHODS

Human immunodeficiency virus (HIV)-seropositive patients with biopsy-confirmed KS that progressed over the 2 months before enrollment received an initial dose of 200 mg/d of oral thalidomide in a phase II study. The dose was increased to a maximum of 1,000 mg/d for up to 1 year. Anti-HIV therapy was maintained during the study period. Toxicity, tumor response, immunologic and angiogenic factors, and virologic parameters were assessed.

RESULTS

Twenty patients aged 29 to 49 years with a median CD4 count of 246 cells/mm(3) (range, 14 to 646 cells/mm(3)) were enrolled. All patients were assessable for toxicity, and 17 for response. Drowsiness in nine and depression in seven patients were the most frequent toxicities observed. Eight (47%; 95% confidence interval [CI], 23% to 72%) of the 17 assessable patients achieved a partial response, and an additional two patients had stable disease. Based on all 20 patients treated, the response rate was 40% (95% CI, 19% to 64%). The median thalidomide dose at the time of response was 500 mg/d (range, 400 to 1,000 mg/d). The median duration of drug treatment was 6.3 months, and the median time to progression was 7.3 months.

CONCLUSION

Oral thalidomide was tolerated in this population at doses up to 1,000 mg/d for as long as 12 months and was found to induce clinically meaningful anti-KS responses in a sizable subset of the patients. Additional studies of this agent in KS are warranted.

The role of chemokines in Hodgkin's disease

Recent studies have analyzed the expression of chemokines in tissues involved by Hodgkin's disease (HD) (1). The data indicate a significant role for chemokine expression in the pathobiology and pathophysiology of HD. In general, HD tissues showed higher levels of chemokine expression than reactive lymphoid hyperplasia (RLH) tissues. There were major differences in chemokine expression among the different HD subtypes. Similar to previous studies in athymic mice that identified a pattern of chemokine response induced by Epstein-Barr virus (EBV)-infected cells, the expression of IP-10, Mig, RANTES, and MIP1-alpha was higher in EBV positive compared to EBV negative HD tissues. In addition, there was a direct correlation of eotaxin expression with tissue eosinophilia. By immunohistochemistry, IP-10 and Mig proteins localized in the malignant Reed-Steinberg (RS) cells and their variants, and to some surrounding inflammatory cells. Eotaxin localized to fibroblasts and smooth muscle of blood vessels. In this review, we discuss the patterns of expression of IP-10, Mig, RANTES, MIP1-alpha, and eotaxin in HD and its subtypes, and the relationship to EBV positivity, LMP1 expression, tissue eosinophilia and T cell infiltration. In addition, we discuss the potential role of chemokines and cytokines in the pathobiology of HD.

Contribution of automated hematology analysis to the detection of apoptosis in peripheral blood lymphocytes

Automated hematology analyzers (analyzers) can provide complete blood counts and white blood cell (WBC) differentials in clinical laboratories and alert users to the presence of quantitative and qualitative cell abnormalities through cautionary flags. In this study, we applied analyzers to the screening of apoptotic cells in peripheral blood and examined the triggering capacity of cautionary flags to detect apoptotic cell populations. EDTA-anticoagulated fresh peripheral blood from patients with acute infectious mononucleosis containing atypical lymphocytes comprising 12.3 +/- 4. 0% of WBC was applied to a Beckman-Coulter MAXM A/L Retic (MAXM) analyzer. The lymphocyte cluster spread upward in VOLUME/DF1 scattergrams and the threshold lines between lymphocyte and monocyte clusters shifted upward. Flags for the number and percentage of lymphocytes, variant lymphocytes, and blast cells were generally present for samples containing atypical lymphocytes. After the blood from acute infectious mononucleosis patients was incubated for 4 h at 37 degrees C, peripheral blood smears revealed the presence of morphologically apoptotic cells comprising 9.0 +/- 4.2% of WBC and a comparable reduction of lymphocytes. On the MAXM analyzer, the apoptotic lymphocyte cluster appeared under the lymphocyte cluster in VOLUME/DF1 scattergrams. However, no specific flag was present to alert users to the presence of the apoptotic lymphocyte cluster. We conclude that visual inspection of scattergrams generated by the MAXM analyzer can be useful for the detection of apoptotic lymphocytes in peripheral blood. Cytometry (Comm. Clin. Cytometry) 42:209-214, 2000. Published 2000 Wiley-Liss, Inc.

Large deletion of the X-linked lymphoproliferative disease gene detected by fluorescence in situ hybridization

The X-linked lymphoproliferative disease (XLP) is an inherited immunodeficiency characterized by an abnormal responses to infection with Epstein-Barr virus (EBV), resulting in fatal infectious mononucleosis, hypogammaglobulinemia, virus-associated hemophagocytic syndrome, and malignant lymphoma. Mutations in the gene coding for a T cell-specific SLAM-associated protein (SAP) have been recently identified in XLP patients. We report on a 1-year-old boy representing fulminant hemophagocytic syndrome. He developed high fever, lymphadenopathy, hepatosplenomegaly with liver dysfunction, and pancytopenia with marrow hemophagocytosis. EBV DNA was abnormally increased in the blood. Polymerase chain reaction failed to amplify SAP mRNA and genomic DNA products from the patient' As peripheral blood. A large deletion of the SAP gene was confirmed by fluorescence in situ hybridization (FISH). FISH analysis also disclosed that the patient's mother was a carrier. We conclude that FISH can be useful in the diagnosis of XLP with large deletions of the SAP gene and its carrier state.

Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6

Since the discovery of the virus in 1994, the rapid pace with which Karposi's sarcoma-associated herpesvirus (KSHV) research has progressed has quickly led to a broad understanding of the structure of the virus and its biology and pathology in humans. Molecular piracy of potentially useful cellular genes has emerged as a characteristic feature of this virus. The viral homolog of human IL-6, vIL-6 is an example in kind. Studies in vitro and in vivo have shown that vIL-6 can stimulate the growth of KSHV-infected primary infusion lymphoma (PEL) cells, can promote hematopoiesis, and act as an angiogenic factor through the induction of vascular endothelial growth factor (VEGF). It is not difficult to envision how vIL-6, through these properties and perhaps others yet to be identified, can contribute to KSHV survival and spread in the human population.

Role of vascular endothelial growth factor/vascular permeability factor in the pathogenesis of Kaposi's sarcoma-associated herpesvirus-infected primary effusion lymphomas

Primary effusion lymphomas (PELs), which are rare lymphomas associated with Kaposi's sarcoma-associated herpesvirus (or human herpesvirus-8) infection, present as malignant lymphomatous effusions in body cavities. Because PELs prefer liquid growth, we hypothesized that increased vascular permeability would be required for effusions to form. We found that the PEL cell lines BC-1, BCP-1, and BCBL-1 produce high levels of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). Reverse transcriptase-polymerase chain reaction analysis of RNA from the PEL cell lines amplified the 3 VEGF-secreted isoforms: VEGF/VPF(121), VEGF/VPF(145), and VEGF/VPF(165). Two of the PEL cell lines expressed the VEGF/VPF receptor Flt-1, but VEGF/VPF did not stimulate proliferation in these cells. Most (13/14) control SCID/beige mice inoculated intraperitoneally with BCBL-1 cells and subsequently observed or treated with control antibodies developed effusion lymphoma of human cell origin with prominent bloody ascites. In contrast, none (0/9) of the mice treated with a neutralizing antihuman VEGF/VPF antibody developed ascites and effusion lymphoma. These results demonstrate that VEGF/VPF is critical to BCBL-1 growth as effusion lymphoma in mice and suggest that VEGF/VPF stimulation of vascular permeability may be critical to the pathogenesis of PELs.

MIP-1alpha expression in tissues from patients with hemophagocytic syndrome

Hemophagocytic syndrome (HPS) is a clinicopathologic syndrome that can be precipitated by a variety of causes and is characterized by a systemic activation of macrophages, which are induced to undergo phagocytosis. Chemokines play an important role in the inflammatory cell recruitment into tissues. We examined the expression of chemokines and cytokines in tissues exhibiting histologic evidence of HPS in a variety of settings: peripheral T-cell lymphoma, three patients; nasal T/NK cell lymphoma, one patient; subcutaneous panniculitis-like T-cell lymphoma, one patient; and chronic EBV infection, one patient. Compared with control tissues, we found elevated macrophage inflammatory protein-1alpha (MIP-1alpha) and interferon-gamma (IFN-gamma) expression, but not macrophage-derived chemotactic factor (MDC) or TNF-alpha, in tissues of patients with HPS irrespective of the cause or setting. MIP-1alpha can promote macrophage chemotaxis and IFN-gamma promotes macrophage activation. Elevated expression of IP-10 and monokine induced by IFN-gamma (Mig) was also detected in tissues exhibiting features of HPS, providing an explanation for the occurrence of chemoattraction of T-cells and NK cells. Immunohistochemical analysis of tissues with evidence of phagocytic activity in that site showed MIP-1alpha characteristically localized to endothelial cells of blood vessels and splenic sinuses, lymphocytes, and macrophages. These results provide evidence for MIP-1alpha chemokine expression in tissues from patients with HPS and suggest that MIP-1alpha may play an important role in the pathogenesis of the hemophagocytic syndrome.

Involvement of interleukin-10 (IL-10) and viral IL-6 in the spontaneous growth of Kaposi's sarcoma herpesvirus-associated infected primary effusion lymphoma cells

Primary effusion lymphoma (PEL) is a distinct type of lymphoma associated with Kaposi's sarcoma-associated herpesvirus (KSHV) infection. To determine the factors responsible for the unrestrained proliferation of PEL, we have studied the growth factor requirements of the PEL-derived BCBL-1 and BC-1 cell lines. Both cell lines were found to be autocrine growth factor dependent and to release human interleukin-6 (IL-6), viral IL-6 (vIL-6), and human IL-10 in the culture supernatant. To establish whether these cytokines contribute to autocrine growth, neutralizing antibodies against human IL-6, vIL-6, human IL-10, and soluble IL-10 receptor were used. These experiments showed that human IL-10 and, to a lesser degree, vIL-6 serve as autocrine growth factors for BCBL-1 and BC-1 cells. Thus, human IL-10 and vIL-6 are growth factors released and used by PEL cells for autonomous proliferation and may be critical to the development and progression of PEL.

Calreticulin and calreticulin fragments are endothelial cell inhibitors that suppress tumor growth

Several angiogenesis inhibitors are fragments of larger proteins that are themselves not active as angiogenesis inhibitors. Vasostatin, the N-terminal domain of calreticulin inclusive of amino acids 1-180, is an angiogenesis inhibitor that exerts antitumor effects in vivo. In the present study, we examined whether the full-length calreticulin molecule shares the antiangiogenic and antitumor activities of vasostatin. Similar to vasostatin, calreticulin selectively inhibited endothelial cell proliferation in vitro, but not cells of other lineages, and suppressed angiogenesis in vivo. When inoculated into athymic mice, calreticulin inhibited Burkitt tumor growth comparably with vasostatin. Calreticulin lacking the N-terminal 1-120 amino acids inhibited endothelial cell proliferation in vitro and Burkitt tumor growth in vivo comparably with vasostatin. An internal calreticulin fragment encompassing amino acids 120-180 also inhibited endothelial cell proliferation in vitro and angiogenesis in vivo comparably with calreticulin and vasostatin. These results suggest that the antiangiogenic activities of vasostatin reside in a domain that is accessible from the full-length calreticulin molecule and localize to calreticulin N-terminal amino acids 120-180. Thus, calreticulin and calreticulin fragments are inhibitors of angiogenesis that directly target endothelial cells, inhibit angiogenesis, and suppress tumor growth. This information may be critical in designing targeted inhibitors of pathological angiogenesis that underlies cancer and other diseases.

Development of EBV-positive T-cell lymphoma following infection of peripheral blood T cells with EBV

Chronic active Epstein-Barr virus (EBV) infection is manifested clinically by the persistence of infectious mononucleosis-like symptoms or its complications for a prolonged period ranging from one to several years. This syndrome may include severe disease manifestations and can be fatal. The role of EBV in the pathogenesis of chronic active EBV infection has been unclear. We investigated two Japanese patients with severe chronic active EBV infection who subsequently developed EBV-positive T-cell lymphoma. We found that the patients had evidence of EBV infection in the peripheral blood CD4+ T-cells 19 and 3 months, respectively, before the T-cell lymphoma was diagnosed. The lymphomas were infected with monoclonal EBV and expressed the EBV latency genes EBNA-1, LMP-1, and LMP-2A, a virus latency pattern referred to as latency II. Genetic studies showed that the virus detected in the T-cell lymphoma was indistinguishable from the virus in the peripheral blood CD4+ T-cells. These studies support an important pathogenetic role of T-cell infection with EBV in chronic active EBV infection and in the EBV-positive T-cell lymphoma that followed.

Interleukin-18, interferon-gamma, IP-10, and Mig expression in Epstein-Barr virus-induced infectious mononucleosis and posttransplant lymphoproliferative disease

T cell immunodeficiency plays an important role in the pathogenesis of posttransplant lymphoproliferative disease (PTLD) by permitting the unbridled expansion of Epstein-Barr virus (EBV)-infected B lymphocytes. However, factors other than T cell function may contribute to PTLD pathogenesis because PTLD infrequently develops even in the context of severe T cell immunodeficiency, and athymic mice that are T-cell-immunodeficient can reject EBV-immortalized cells. Here we report that PTLD tissues express significantly lower levels of IL-18, interferon-gamma (IFN-gamma), Mig, and RANTES compared to lymphoid tissues diagnosed with acute EBV-induced infectious mononucleosis, as assessed by semiquantitative RT-PCR analysis. Other cytokines and chemokines are expressed at similar levels. Immunohistochemistry confirmed that PTLD tissues contain less IL-18 and Mig protein than tissues with infectious mononucleosis. IL-18, primarily a monocyte product, promotes the secretion of IFN-gamma, which stimulates Mig and RANTES expression. Both IL-18 and Mig display antitumor activity in mice involving inhibition of angiogenesis. These results document greater expression of IL-18, IFN-gamma, Mig, and RANTES in lymphoid tissues with acute EBV-induced infectious mononucleosis compared to tissues with PTLD and raise the possibility that these mediators participate in critical host responses to EBV infection.

Angiogenesis and hematopoiesis induced by Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6

Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 [HHV-8]) is a herpesvirus linked to the development of Kaposi's sarcoma (KS), primary effusion lymphoma, and a proportion of Castleman's disease. KSHV encodes viral interleukin-6 (vIL-6), which is structurally homologous to human and murine IL-6. The biological activities of vIL-6 are largely unknown. To gain insight into the biology of vIL-6, we expressed vIL-6 in murine fibroblasts NIH3T3 cells and inoculated stable vIL-6-producing clones into athymic mice. vIL-6 was detected selectively in the blood of mice injected with vIL-6-expressing clones. Compared with controls, vIL-6-positive mice displayed increased hematopoiesis in the myeloid, erythroid, and megakaryocytic lineages; plasmacytosis in spleen and lymph nodes; hepatosplenomegaly; and polyclonal hypergammaglobulinemia. vIL-6-expressing NIH3T3 cells gave rise to tumors more rapidly than did control cells, and vIL-6-positive tumors were more vascularized than controls. Vascular endothelial growth factor (VEGF) was detected at higher levels in the culture supernatant of vIL-6-expressing cells compared with controls, and immunohistochemical staining detected VEGF in spleen, lymph nodes, and tumor tissues from mice bearing vIL-6-producing tumors but not control tumors. Thus, vIL-6 is a multifunctional cytokine that promotes hematopoiesis, plasmacytosis, and angiogenesis. Through these functions, vIL-6 may play an important role in the pathogenesis of certain KSHV-associated disorders.

The Italian Multicentric Study on Epidemiology of Congenital Heart Disease: first step of the analysis. Working Party of the Italian Society of Pediatric Cardiology

We present the aims, methodology and initial results from the Italian Multicentric Study for the registration and follow-up of congenital heart disease. The general aims are to measure the prevalence of congenital heart disease in different geographic areas of Italy, and to assess the survival and outcome of affected babies. During the years 1992 and 1993, eighteen centers for Pediatric Cardiology spread all over the Country enrolled 1445 new babies with congenital cardiac malformations from a population of 341,647 surveyed livebirths. The new cases were registered using the same methodologic criteria of the EUROCAT study in order to evaluate differences and/or similarities between the studies. The prevalence varied between 1.8% and 8.1%; the average being 4.6%. The large range in prevalence is presumed to be related to different customs and hierarchies in flow and referral of patients. We provide total prevalence of individual lesions, and distribution of sentinel cardiac anomalies, in the Italian study and compare them with EUROCAT. Isolated ventricular septal defect is the most common lesion (39%); followed by atrial septal defect (7.5%); pulmonary valvar stenosis (7.3%); atrioventricular septal defects (5.4%); patency of the arterial duct (3.8%); complete transposition (3.7%); tetralogy of Fallot (3.3%); aortic coarctation (2.4%); aortic valvar stenosis (2.2%); and left heart hypoplasia (1.8%). The echographic stratification of ventricular and atrial septal defects, by location and size, was in keeping with the findings of the EUROCAT study. Because of the recent widespread availability of color-Doppler techniques, the stratification of aortic and pulmonary valvar stenosis was an innovative approach in our study. Among the complex cardiovascular anomalies, double inlet ventricle and pulmonary atresia had a proportion of about 2% each; with double outlet right ventricle, common arterial trunk, Ebstein's malformation, tricuspid atresia, interrupted aortic arch and totally anomalous pulmonary venous connection having a proportion ranging from 0.5 to 0.8%. We discuss clinical features, such as frequency of extracardiac anomalies and familial aggregation of congenital heart disease, in comparison with the EUROCAT data.

Differential chemokine expression in tissues involved by Hodgkin's disease: direct correlation of eotaxin expression and tissue eosinophilia

Hodgkin's disease (HD) is a lymphoid malignancy characterized by infrequent malignant cells surrounded by abundant inflammatory cells. In this study, we examined the potential contribution of chemokines to inflammatory cell recruitment in different subtypes of HD. Chemokines are small proteins that are active as chemoattractants and regulators of cell activation. We found that HD tissues generally express higher levels of interferon-gamma-inducible protein-10 (IP-10), Mig, RANTES, macrophage inflammatory protein-1alpha (MIP-1alpha), and eotaxin, but not macrophage-derived chemotactic factor (MDC), than tissues from lymphoid hyperplasia (LH). Within HD subtypes, expression of IP-10 and Mig was highest in the mixed cellularity (MC) subtype, whereas expression of eotaxin and MDC was highest in the nodular sclerosis (NS) subtype. A significant direct correlation was detected between evidence of Epstein-Barr virus (EBV) infection in the neoplastic cells and levels of expression of IP-10, RANTES, and MIP-1alpha. Levels of eotaxin expression correlated directly with the extent of tissue eosinophilia. By immunohistochemistry, IP-10, Mig, and eotaxin proteins localized in the malignant Reed-Sternberg (RS) cells and their variants, and to some surrounding inflammatory cells. Eotaxin was also detected in fibroblasts and smooth muscle cells of vessels. These results provide evidence of high level chemokine expression in HD tissues and suggest that chemokines may play an important role in the recruitment of inflammatory cell infiltrates into tissues involved by HD.

Increased cell-free viral DNA in fatal cases of chronic active Epstein-Barr virus infection

We have studied the nature of Epstein-Barr virus (EBV) infection in 33 patients with chronic active EBV infection. The study population included 14 patients with fatal chronic EBV infection and 19 patients with nonfatal chronic EBV infection, as well as 18 patients with acute EBV-induced infectious mononucleosis and 10 healthy controls. EBV DNA was measured in serum or plasma samples from the patients by semiquantitative polymerase chain reaction-based assay. EBV DNA was detected in serum or plasma samples from 62% (9/14) of patients with fatal chronic active EBV infection. In contrast, only 11% (2/19) of patients with nonfatal chronic active EBV infection and 11% (2/18) of patients with infectious mononucleosis displayed EBV DNA. None of the healthy controls tested positive. Cell-free circulating EBV DNA may represent an important feature of chronic active EBV infection and may provide a useful tool to monitor the severity of this illness.

Contribution of natural killer cells to inhibition of angiogenesis by interleukin-12

Interleukin-12 (IL-12) inhibits angiogenesis in vivo by inducing interferon-gamma (IFN-gamma) and other downstream mediators. Here, we report that neutralization of natural killer (NK) cell function with antibodies to either asialo GM1 or NK 1.1 reversed IL-12 inhibition of basic fibroblast growth factor (bFGF)-induced angiogenesis in athymic mice. By immunohistochemistry, those sites where bFGF-induced neovascularization was inhibited by IL-12 displayed accumulation of NK cells and the presence of IP-10-positive cells. Based on expression of the cytolytic mediators perforin and granzyme B, the NK cells were locally activated. Experimental Burkitt lymphomas treated locally with IL-12 displayed tumor tissue necrosis, vascular damage, and NK-cell infiltration surrounding small vessels. After activation in vitro with IL-12, NK cells from nude mice became strongly cytotoxic for primary cultures of syngeneic aortic endothelial cells. Cytotoxicity was neutralized by antibodies to IFN-gamma. These results document that NK cells are required mediators of angiogenesis inhibition by IL-12, and provide evidence that NK-cell cytotoxicity of endothelial cells is a potential mechanism by which IL-12 can suppress neovascularization.

Bax is frequently compromised in Burkitt's lymphomas with irreversible resistance to Fas-induced apoptosis

We have analyzed the Fas-mediated death pathway in a panel of 11 Epstein-Barr virus (EBV)-negative and 10 EBV-positive Burkitt's lymphoma (BL) cell lines. We show that the increased expression of Fas in EBV-positive cell lines is mediated via LMP-1. Four of the 21 BL cell lines are readily responsive to Fas-mediated cell death signals. Of the remaining 17 cell lines, 10 can be sensitized by up-regulating Fas either via exogenous expression of LMP-1 or via treatment with CD40L. These same cell lines can also be sensitized by treatment with cycloheximide (CHX), which, however, does not result in up-regulation of Fas. Neither up-regulation of Fas, nor treatment with CHX, restore Fas sensitivity in seven BL cell lines. Further analyses indicated that 5 of the 7 cell lines (and none of the 14 responsive cell lines) were also compromised in the integrity/expression of the proapoptotic gene Bax. Thus, in most BL cell lines, the Fas pathway seems to be inhibited, although the mechanism of inhibition varies. The correlation between Bax mutation and irreversible (by CD40L or CHX) Fas resistance raises the possibility, for the first time, that Bax may play a critical function in Fas-mediated cell death in BL.

Vasostatin, a calreticulin fragment, inhibits angiogenesis and suppresses tumor growth

An endothelial cell inhibitor was purified from supernatant of an Epstein-Barr virus-immortalized cell line and identified as fragments of calreticulin. The purified recombinant NH2-terminal domain of calreticulin (amino acids 1-180) inhibited the proliferation of endothelial cells, but not cells of other lineages, and suppressed angiogenesis in vivo. We have named this NH2-terminal domain of calreticulin vasostatin. When inoculated into athymic mice, vasostatin significantly reduced growth of human Burkitt lymphoma and human colon carcinoma. Compared with other inhibitors of angiogenesis, vasostatin is a small, soluble, and stable molecule that is easy to produce and deliver. As an angiogenesis inhibitor that specifically targets proliferating endothelial cells, vasostatin has a unique potential for cancer treatment.

Expression of human herpesvirus-8 oncogene and cytokine homologues in an HIV-seronegative patient with multicentric Castleman's disease and primary effusion lymphoma

Human herpesvirus-8 (HHV-8) has been described in association with two lymphoproliferative disorders: one benign, multicentric Castleman's disease (MCD), and one malignant, primary effusion lymphoma (PEL). The factors that lead to malignant transformation of lymphoid cells are unknown, although most cases of PEL also are positive for EBV, suggesting a role for EBV as a cofactor in malignant transformation. We encountered a rare case of an HHV-8-associated MCD, followed by the development of an HHV-8-positive pleural PEL and a gastric large cell lymphoma in an HIV-seronegative male patient. The lesions were negative for Epstein-Barr virus (EBV). The combination of these diverse HHV-8-associated lymphoproliferative disorders in a single patient afforded us the ability to study potential differences in gene expression in these conditions. HHV-8 DNA was demonstrated by PCR in lymphoid tissues involved by MCD and PEL. By reverse transcriptase-PCR, HHV-8-related transcripts, including vG-coupled protein receptor, vbcl2, vcyclin D, vIL-6, vMIPI, and vMIPII, were detected in the PEL from the pleural cavity and the gastric lymphoma, whereas these transcripts, except for vIL-6, were not detected in a lymph node biopsy with MCD. Expression of hIL-10 was weak in the PEL from the pleural cavity, and expression of hIL-6 was undetectable in all three lesions. These data suggest that vIL-6 may be integral to the pathogenesis of MCD, whereas other viral transcripts that encode oncogene and chemokine homologues are important for HHV-8 tumorigenicity.

Contribution of the CXC chemokines IP-10 and Mig to the antitumor effects of IL-12

The mechanisms by which interleukin-12 (IL-12) exerts antitumor effects have been difficult to dissect. In this study, we examined the potential contribution of the chemokines interferon-gamma-inducible protein-10 (IP-10) and Mig to the antitumor effects of IL-12. Using an athymic mouse model, local inoculations with IL-12 consistently produced tumor size reductions associated with characteristic tumor necrosis and vascular damage. These effects were indistinguishable from those produced by IP-10 or Mig injected locally in the same tumor model. Local and systemic treatment with IL-12 was associated with expression of the interferon-gamma (IFN-gamma), IP-10, and Mig genes and proteins in the tumor. Levels of IP-10 and Mig expression in the tumor, the liver, and the kidney were inversely correlated with tumor size. Administration in vivo of neutralizing antibodies to IP-10 and Mig reduced substantially the antitumor effects of IL-12 inoculated locally into the tumors. These results support the notion that IP-10 and Mig contribute to the antitumor effects of IL-12 through their inhibitory effects on tumor vasculature.

EBV-NK cells interactions and lymphoproliferative disorders

Epstein-Barr virus (EBV) usually infects epithelial cells in the oropharynx and B lymphocytes asymptomatically. Occasionally, however, EBV infects T-cells and natural killer (NK) cells, and infection of these cells has been associated with the development of leukemias and lymphomas. EBV-positive lymphoproliferative disorders of NK cells have been reported with increasing frequency, but the interactions between EBV and NK cells are not fully understood, in part because NK cells are not usually infected with EBV in vitro. The lymphoma-derived EBV-positive NK cell line, YT, has been useful in the study of EBV infection of NK cells. YT cells express the EBV-associated nuclear antigen (EBNA)-1, the latent membrane protein (LMP)-1, and LMP-2A, but not EBNA-2 and LMP-2B genes. This pattern of latent gene expression is compatible with a type II latency program, normally associated with nasopharyngeal carcinoma, Hodgkin's disease, and T-cell lymphoma. In this report, we summarize recent information on EBV-NK cell interactions and EBV-positive lymphoproliferative disorders of NK cells.

Expression of the Epstein-Barr virus protein LMP1 mediates tumor regression in vivo

By stimulating the expression of murine IP-10 and Mig, CXC chemokines that inhibit neovascularization and cause damage to established tumor vasculature, human B cells immortalized with Epstein-Barr virus (EBV) can promote an effective antitumor response in athymic mice. In the present study, we examined the potential role of EBV in the induction of this antitumor response. Using a panel of EBV+ and EBV- Burkitt lymphoma (BL) cell lines, a significant correlation was detected between the expression of the EBV latency gene LMP1 and the occurrence of spontaneous tumor regression in athymic mice. Inoculation of LMP1+ and LMP1- BL cells in the same subcutaneous site resulted in tumors that completely regressed in a manner indistinguishable from that induced by EBV-immortalized B cells. EBV-converted BL30 and BL41 sublines infected with B95-8 virus expressed LMP1, generated tumors that frequently regressed spontaneously, and promoted an effective antitumor response against progressively growing tumors. In contrast, the EBV- BL30 and BL41 cell lines and the EBV-converted BL30 and BL41 infected with P3HR-1 virus did not express LMP1 protein, and generated progressively growing tumors in nude mice. When transfected with the LMP1 gene, BL41 cells produced tumors that regressed spontaneously in most cases, and could induce the regression of tumors derived from BL41 cells transfected with vector alone. Tumors induced by LMP1-expressing cells expressed murine IP-10 and Mig and displayed histological evidence of extensive tumor tissue necrosis and vascular damage. We conclude that the EBV protein LMP1 is likely responsible for the antitumor response elicited by EBV-immortalized cells in athymic mice.

A syndrome of peripheral blood T-cell infection with Epstein-Barr virus (EBV) followed by EBV-positive T-cell lymphoma

The role of Epstein-Barr virus (EBV) in the pathogenesis of severe, chronic active EBV infection and its complications is unclear. We investigated two Japanese patients diagnosed with severe, chronic active EBV infection who subsequently developed EBV-positive T-cell lymphoma. The patients displayed abnormally high antibody titers to EBV antigens, and had evidence of peripheral blood CD4(+) T-cell infection with EBV, 19 months and 3 months, respectively, before the diagnosis of EBV-positive T-cell lymphoma. The lymphomas were infected with monoclonal EBV and expressed the EBV latency genes EBNA-1, LMP-1, and LMP-2. Genetic studies showed that the virus detected in the T-cell lymphoma was indistinguishable, with respect to type and previously defined LMP-1 and EBNA-1 gene variations, from virus detected in the peripheral blood T cells 19 months earlier. These studies support an important pathogenetic role of T-cell infection with EBV in chronic active EBV infection and in the EBV-positive T-cell lymphoma that followed.

The role of Mig, the monokine induced by interferon-gamma, and IP-10, the interferon-gamma-inducible protein-10, in tissue necrosis and vascular damage associated with Epstein-Barr virus-positive lymphoproliferative disease

The mechanisms of tissue necrosis and vascular damage characteristics of certain Epstein-Barr virus (EBV)-associated lymphoproliferative disorders are unknown. The CXC chemokines interferon-gamma-inducible protein-10 (IP-10) and the monokine induced by interferon-gamma (Mig) caused tissue necrosis and vascular damage in Burkitt's lymphoma tumors established in nude mice. We report higher levels of IP-10 and Mig gene expression in tissues with necrosis and vascular damage from EBV-positive lymphomatoid granulomatosis and nasal or nasal-type T/natural killer (NK)-cell lymphomas compared with tissues with lymphoid hyperplasia, which lacked tissue necrosis and vascular damage. By immunohistochemistry, Mig and IP-10 proteins localized with similar patterns in viable tissue surrounding dead tissue, mostly within endothelial cells, monocyte/macrophages, and lymphocytes. Circulating levels of IP-10 were abnormally elevated in patients with EBV-positive lymphomatoid granulomatosis and nasal or nasal-type T/NK-cell lymphomas. These experiments provide the first description of the presence of Mig in any human normal or diseased tissue and the first description of IP-10 in certain lymphoproliferative lesions. These data suggest that Mig and IP-10 play an important role in the pathogenesis of tissue necrosis and vascular damage associated with certain EBV-positive lymphoproliferative processes.

Viral interleukin-10 in chronic active Epstein-Barr virus infection

Viral interleukin-10 (IL-10), a product of the Epstein-Barr virus (EBV) replication gene BCRF1, shares extensive structural and functional similarity with the human cytokine IL-10. Both viral and human IL-10 inhibit T cell growth and interferon-gamma production. With two ELISAs, one that recognized both human and viral (total) IL-10 and the other specific for viral IL-10, IL-10 was measured in serum or plasma from 34 patients with chronic active EBV infection (CAEBV) and from 15 healthy controls. Of the patients, 56% had measurable total IL-10 and 29% had measurable viral IL-10. In contrast, total IL-10 was detectable in only 2 of 15 controls and viral IL-10 was undetectable. Thus, many patients with CAEBV have abnormally high levels of circulating IL-10 that may contribute to disease pathogenesis by inhibiting host immunity.

Role of the p53 tumor suppressor gene in the tumorigenicity of Burkitt's lymphoma cells

Burkitt's lymphoma (BL) cell lines carry a translocated c-myc gene and, in 60-80% of cases, exhibit mutations in the p53 tumor suppressor gene. We examined the potential role of the p53 gene in BL tumorigenicity using an in vitro assay that measures p53-dependent cell cycle arrest in the G1 phase of the cell cycle and an in vivo athymic murine model that detects differences in the tumorigenicity of BL cell lines. A highly significant inverse correlation was found between the ability of BL cells to arrest in G1 after irradiation and their tumorigenicity in athymic mice, consistent with the notion that loss of p53 function is associated with increased tumorigenicity. Inactivation of wild-type (wt) p53 function by expression of the human papillomavirus E6 protein in the AG876V BL cell line, which carries both wt and mutant p53 proteins, rendered the cell line significantly more tumorigenic in athymic mice. Transfection of the wt p53 gene into the p53 mutant and highly tumorigenic BL-41 cell line caused it to acquire wt p53 function and rendered it less tumorigenic in mice. In addition to confirming a role for the loss of p53 function in tumor progression, the data demonstrate that wt p53 protein can reduce BL tumorigenicity in vivo.