Biology of Kaposi's sarcoma

Epidemiology of HHV-8 infection in HIV-positive patients with and without Kaposi sarcoma: diagnostic relevance of serology and PCR

BACKGROUND

Kaposi's sarcoma (KS) remains the most common neoplasm in HIV-infected patients. Human herpesvirus 8 (HHV-8) infection is etiologically associated with KS. Diagnostic procedures with regard to HHV-8 infection are not routinely performed in HIV-infected patients; diagnostic and prognostic value of HHV-8 serology or PCR are unknown in this setting. Epidemiological data concerning HHV-8 infection of HIV-infected patients in Germany are rare.

OBJECTIVES

To assess prevalence of HHV-8 infection in a cohort of HIV-infected patients with and without KS in Germany and to correlate this to manifestations and clinical course of KS.

STUDY DESIGN

HHV-8 serology was performed in 483 patients in routine care for HIV-infection in northern Germany. HHV-8 DNA was analyzed by PCR in peripheral blood mononuclear cells (PBMC) of 293 patients; in a subgroup multiple samples were analyzed. History and manifestations of KS were recorded.

RESULTS

HHV-8 antibodies were detected using IFT in 91% of 33 patients with KS and 52% of 398 patients without KS. In 36 of 293 (12.3%) patients HHV-8 DNA was detected in PBMC. In general, HHV-8 DNA was not continuously detected when multiple samples from the same patient were analyzed. Patients with KS history were more likely to be PCR positive than those without (45.5% versus 7.8%). In patients with active KS HHV-8 DNA was detected more frequently than in patients with disease remission. HHV-8 DNA was not detected in serologically negative patients. However, three patients with KS history in full remission for several years were seronegative.

CONCLUSIONS

HIV-infected patients were frequently found to be positive for HHV-8 antibodies. The number of patients positive for viral DNA in PBMC was much smaller. Single PCR-examinations were of little value for prognosis, but repeated detection of HHV-8 DNA represents an increased risk of disease activity.

Chemokines and Kaposi’s sarcoma

Chemokines participate in many biological processes in homeostasis and disease. Recently, they have been implicated in cancer, more specifically in tumor angiogenesis and metastasis. Here we review evidence supporting a role for chemokines in the pathogenesis of Kaposi's sarcoma and discuss a possible role for these molecules in angioproliferation and immune evasion.

Canine malignant hemangiosarcoma as a model of primitive angiogenic endothelium

Hemangiosarcoma (HSA) is a common untreatable cancer of dogs that resembles human angiosarcoma. Detailed studies of these diseases have been historically hindered by the paucity of suitable reagents. Here, we show that expression of CD117 (c-Kit) can distinguish primitive (malignant) from mature (benign) proliferative endothelial lesions, and we describe eight independent cell lines derived from canine HSA explants. Endothelial origin was confirmed by sustained expression of surface CD105 (endoglin), CD146 (MUC18), and CD51/CD61 (alpha(v)beta(3) integrin). The cell lines showed anchorage-independent growth and were motile and invasive when cultured on a basement membrane matrix. They required endothelial growth factors for growth and survival, and they could be induced to form tubular structures resembling blood vessels when cultured under low calcium conditions. The formation of vessel-like structures was blocked by nicotine, and restored by FK506, suggesting that 'nuclear factor of activated T cells' activity prevents differentiation of these cells. In summary, these cell lines represent a unique and novel resource to improve our understanding of endothelial cell biology in general and canine HSA in particular.

Viral Bcl-2 homologs and their role in virus replication and associated diseases

Cellular Bcl-2 family proteins regulate a critical step in the mammalian programmed cell death pathway by modulating mitochondrial permeability and function. Bcl-2 family proteins are also encoded by several large DNA viruses, including all known gamma herpesviruses, adenoviruses, and several other unrelated viruses. Viral Bcl-2 proteins can prevent cell death but often escape cellular regulatory mechanisms that govern their cellular counterparts. By evading the "altruistic" suicide of infected cells, viruses can ensure replication and propagation in the infected host, but sometimes in surprising ways. Many human cancers and other disorders are associated with viruses that encode Bcl-2 homologs. Here we consider the available mechanistic data for viral compared to cellular Bcl-2 protein function along with relevance to the virus life cycle and human disease states.

Lytic KSHV infection inhibits host gene expression by accelerating global mRNA turnover

The stimulation of host gene expression by lytic gene products of Kaposi's sarcoma-associated herpesvirus (KSHV) has been proposed to play a critical role in KS development. We show, however, that lytic KSHV infection strongly inhibits host gene expression early in infection by accelerating global mRNA turnover. This function is mediated by KSHV ORF37, a homolog of a DNA exonuclease widely present in other herpesviruses but which in KSHV has uniquely evolved additional functions that mediate its participation in RNA degradation. The ability of KSHV to inhibit host gene expression has important implications for models of KS pathogenesis that invoke activation of host transcription in lytically infected cells as a source of angiogenic or oncogenic factors.

HHV-8-associated Kaposi sarcoma in a child with IFNgammaR1 deficiency

OBJECTIVES

Mediterranean classic Kaposi sarcoma (KS) of childhood is rare and unexplained. Our objective is to describe the case of a child with complete IFNgammaR1 deficiency and severe mycobacterial disease in whom Kaposi sarcoma (KS) developed.

RESULTS

Disseminated mycobacterial infection began at the age of 5 months, and at 11 years of age the child had disseminated KS lesions. The histologic appearance of these lesions was typical, with endothelial and spindle cell proliferation. Human herpesvirus-8 (HHV-8)-associated antigens were detected in situ by immunohistochemistry. HHV-8 DNA of K1 molecular subtype A was amplified from tissue lesions, and HHV-8-specific antibodies were detected in the patient's serum. The child died at 12 years of age of disseminated mycobacterial disease and KS.

CONCLUSIONS

This is the first identification of a well-defined primary immunodeficiency in a child with KS. Inherited disorders of IFN-gamma-mediated immunity and severe mycobacterial disease may predispose HHV-8-infected children to KS.

Host gene induction and transcriptional reprogramming in Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8)-infected endothelial, fibroblast, and B cells: insights into modulation events early during infection

Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) is etiologically linked to the endothelial tumor Kaposi's sarcoma and with two lymphoproliferatve disorders, primary effusion lymphoma and multicentric Castleman's disease. HHV-8 infects a variety of target cells both in vivo and in vitro, binds to the in vitro target cells via cell surface heparan sulfate, and uses the alpha(3)beta(1) integrin as one of the entry receptors. Within minutes of infection, HHV-8 induced the integrin-mediated signaling pathways and morphological changes in the target cells (S. M. Akula et al., Cell, 108: 407-419, 2002; P. P. Naranatt et al., J. Virol., 77: 1524-1539, 2003). As an initial step toward understanding the role of host genes in HHV-8 infection and pathogenesis, modulation of host cell gene expression immediately after infection was examined. To reflect HHV-8's broad cellular tropism, mRNAs collected at 2 and 4 h after infection of primary human endothelial [human adult dermal microvascular endothelial cells (HMVECd)] and foreskin fibroblast [human foreskin fibroblast (HFF)] cells and human B cell line (BJAB) were analyzed by oligonucleotide array with approximately 22,000 human transcripts. With a criteria of >2-fold gene induction as significant, approximately 1.72% of the genes were differentially expressed, of which, 154 genes were shared by at least two cells and 33 genes shared by all three cells. HHV-8-induced transcriptional profiles in the endothelial and fibroblast cells were closely similar, with substantial differences in the B cells. In contrast to the antiapoptotic regulators induced in HMVECd and HFF cells, proapoptotic regulators were induced in the B cells. A robust increase in the expression of IFN-induced genes suggestive of innate immune response induction was observed in HMVECd and HFF cells, whereas there was a total lack of immunity related protein inductions in B cells. These striking cell type-specific behaviors suggest that HHV-8-induced host cell gene modulation events in B cells may be different compared with the adherent endothelial and fibroblast target cells. Functional clustering of modulated genes identified several host molecules hitherto unknown to HHV-8 infection. These results indicate that early during infection, HHV-8 reprograms the host transcriptional machinery regulating a variety of cellular processes including apoptosis, transcription, cell cycle regulation, signaling, inflammatory response, and angiogenesis, all of which may play important roles in the biology and pathogenesis of HHV-8.

Inflammatory cytokines inhibit Kaposi's sarcoma-associated herpesvirus lytic gene transcription in in vitro-infected endothelial cells

The response of Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) to inflammatory cytokine treatment of experimentally infected endothelial cells was investigated. The cytokines inhibited spontaneous KSHV lytic gene expression but not the level of infection. The data suggest that if inflammatory cytokines present in KS lesions contribute to KSHV pathogenesis, they do so in part by promoting latent KSHV infection of the endothelial cells.

Kaposi’s sarcoma in a patient with severe relapsing polychondritis

This report describes the case of a young man who developed Kaposi's sarcoma (KS) after corticosteroid treatment for severe tracheal involvement of relapsing polychondritis (RP). The etiopathogenetic mechanisms that may have led to the evolution of this unusual neoplasm are discussed. To our knowledge, this is the first case reported of concomitant RP and KS.

Chromatin remodeling of the Kaposi's sarcoma-associated herpesvirus ORF50 promoter correlates with reactivation from latency

The switch from latent to lytic infection of Kaposi's sarcoma-associated herpesvirus is initiated by the immediate early transcriptional activator protein Rta/open reading frame 50 (ORF50). We examined the transcriptional regulation of the ORF50 core promoter in response to lytic cycle stimulation. We show that the ORF50 promoter is highly responsive to sodium butyrate (NaB) and trichostatin A (TSA), two chemicals known to inhibit histone deacetylases. The NaB and TSA responsive element was mapped to a 70-bp minimal promoter containing an essential GC box that binds Sp1/Sp3 in vitro and in vivo. Micrococcal nuclease mapping studies revealed that a nucleosome is positioned over the transcriptional initiation and the Sp1/3 binding sites. Stimulation with NaB or TSA increased histone acetylation and restriction enzyme accessibility of the ORF50 promoter transcription initiation site. Chromatin immunoprecipitation assay was used to demonstrate that the ORF50 promoter is associated with several different histone deacetylase proteins (including HDAC1, 5, and 7) in latently infected cells. NaB treatment led to the rapid association of Ini1/Snf5, a component of the Swi/Snf family of chromatin remodeling proteins, with the ORF50 promoter. Ectopic expression of the CREB-binding protein (CBP) histone acetyltransferase (HAT) stimulated plasmid-based ORF50 transcription in a HAT-dependent manner, suggesting that CBP recruitment to the ORF50 promoter can be an initiating event for transcription and viral reactivation. Together, these results suggest that remodeling of a stably positioned nucleosome at the transcriptional initiation site of ORF50 is a regulatory step in the transition from latent to lytic infection.

HIV protease inhibitors as new treatment options for Kaposi's sarcoma

A reduced incidence and regression of Kaposi's sarcoma (KS) and other tumours has been reported in Acquired Immune Deficiency Syndrome (AIDS) patients treated with antiretroviral combination therapies containing Human Immunodeficiency Virus (HIV) protease inhibitors (PIs) such as indinavir or saquinavir. Indeed, evidence indicates that although PIs were designed to selectively inhibit the HIV protease activity, they can interfere with several cellular pathways and can inhibit tumour growth. In particular, our recent results indicate that doses of indinavir or saquinavir similar to those employed to treat AIDS patients can induce regression of experimental KS by directly blocking two fundamental steps of KS initiation and progression: new blood vessel formation (angiogenesis) and KS tumour cell invasion. This is because indinavir or saquinavir inhibit the activation of matrix metalloproteinase-2 (MMP-2), a basement membrane-degrading enzyme, which is required for the progression of most tumours. Based on these results, a multicentre clinical trial is now starting in Italy, which will assess PI effects on the progression of KS in HIV-uninfected individuals (classical KS).

Structural analysis of the Kaposi's sarcoma-associated herpesvirus K1 protein

The K1 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) efficiently transduces extracellular signals to elicit cellular activation events through its cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM). In addition, the extracellular domain of K1 demonstrates regional homology with the immunoglobulin (Ig) family and contains conserved regions (C1 and C2) and variable regions (V1 and V2). To generate mouse monoclonal antibodies directed against the KSHV K1 protein, BALB/c mice were primed and given boosters with K1 protein purified from mammalian cells. Twenty-eight hybridomas were tested for reactivity with K1 protein by enzyme-linked immunosorbent assay, immunofluorescence, flow cytometry, immunohistochemistry, and immunoblotting. Deletion mutants of the K1 extracellular domain were used to map the epitope of each antibody. All antibodies were directed to the Ig, C1, and C2 regions of K1. Furthermore, antibody recognition of a short sequence (amino acids 92 to 125) of the C2 region overlapping with the Ig region of K1 efficiently induced intracellular free calcium mobilization; antibody recognition of the other regions of K1 did not. The efficient signal transduction of K1 induced by antibody stimulation required both the ITAM sequence of the cytoplasmic domain and the normal structure of the extracellular domain. Finally, immunological assays showed that K1 was expressed during the early lytic cycle of viral replication in primary effusion lymphoma cells. K1 was readily detected in multicentric Castleman's disease tissues, whereas it was not detected in Kaposi's sarcoma lesions, suggesting that K1 is preferentially expressed in lymphoid cells. Thus, these results indicate that the conserved regions, particularly the Ig and C2 regions, of the K1 extracellular domain are exposed on the outer surface and play an important role in K1 structure and signal transduction, whereas the variable regions of K1 appear to be away from the surface.

Epidemiology of AIDS-related malignancies an international perspective

Patients with HIV infection are at increased risk for developing Kaposi's sarcoma, non-Hodgkin's lymphoma, and several other cancers. The relative risks for the most common epithelial cancers in the general population--lung, breast, colon/rectum, stomach, liver, and prostate--are not increased substantially in people with AIDS, however. Accumulating data suggest that HIV-infected patients also are at increased risk for developing Hodgkin's lymphoma, cervical carcinoma in situ (CIS), other anogenital neoplasms (invasive cancer and CIS), leiomyosarcoma, and conjunctival squamous cell carcinoma. There is inconclusive evidence, however, with regard to HIV infection being associated with invasive cervical cancer, testicular seminoma, or hepatocellular carcinoma. Notably, other viral infections have been implicated in the etiology of many of these conditions. The introduction of highly active antiretroviral therapy (HAART) has decreased the incidence of AIDS-associated cancers in Western countries, but less than 1% of AIDS patients are receiving HAART in the HIV epicenter of sub-Saharan Africa. Further therapeutic advances that extend survival with HIV infection with varying reconstitution of immune competence may lead to additional alterations in cancer risk.

Molecular genetics of Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8) epidemiology and pathogenesis

Kaposi's sarcoma had been recognized as unique human cancer for a century before it manifested as an AIDS-defining illness with a suspected infectious etiology. The discovery of Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, in 1994 by using representational difference analysis, a subtractive method previously employed for cloning differences in human genomic DNA, was a fitting harbinger for the powerful bioinformatic approaches since employed to understand its pathogenesis in KS. Indeed, the discovery of KSHV was rapidly followed by publication of its complete sequence, which revealed that the virus had coopted a wide armamentarium of human genes; in the short time since then, the functions of many of these viral gene variants in cell growth control, signaling apoptosis, angiogenesis, and immunomodulation have been characterized. This critical literature review explores the pathogenic potential of these genes within the framework of current knowledge of the basic herpesvirology of KSHV, including the relationships between viral genotypic variation and the four clinicoepidemiologic forms of Kaposi's sarcoma, current viral detection methods and their utility, primary infection by KSHV, tissue culture and animal models of latent- and lytic-cycle gene expression and pathogenesis, and viral reactivation from latency. Recent advances in models of de novo endothelial infection, microarray analyses of the host response to infection, receptor identification, and cloning of full-length, infectious KSHV genomic DNA promise to reveal key molecular mechanisms of the candidate pathogeneic genes when expressed in the context of viral infection.

Expression and purification of recombinant Kaposi's sarcoma-associated herpesvirus DNA polymerase using a Baculovirus vector system

The DNA polymerase (POL) of Kaposi's sarcoma-associated herpesvirus (KSHV) is essential for viral DNA replication and, thus, may be considered as a viable target for anti-KSHV therapeutics. To produce large quantities of homogeneous and pure POL required for high-throughput screening (HTS) for inhibitors, we generated a recombinant baculovirus vector encoding a hexahistidine (His6)-tagged POL and infected Spodoptera frugiperda Sf-9 insect cells. High expression of recombinant POL (rPOL) was achieved for up to 72h post-infection. The rPOL was solubilized in lysis buffer containing 0.3% Cymal-5 detergent, purified by metal-chelating and dsDNA-cellulose affinity chromatography, and analyzed by anti-His antibody Western blot and mass spectrometry. The functionality of rPOL was confirmed by its DNA synthesis activity in vitro, which was effectively blocked by the anti-herpetic DNA polymerase inhibitors, foscarnet and cidofovir diphosphate, in a dose-dependent manner. The POL expressed and purified from the recombinant baculovirus-infected insect cells may be useful toward the development of HTS of large chemical libraries to identify novel KSHV DNA polymerase inhibitors.

Immune deficiency and risk for malignancy among persons with AIDS

BACKGROUND

People with AIDS have an elevated risk for cancer. We studied the relationship between cancer risk and AIDS-related immunosuppression as measured by CD4 count at AIDS onset.

METHODS

We linked records from AIDS and cancer registries in 11 US regions (1990-1996). We studied 82,217 (86.6%) adults who had a CD4 count measured at AIDS onset and survived into the follow-up period. We calculated standardized incidence ratios (SIRs) for AIDS-defining (Kaposi sarcoma [KS], non-Hodgkin lymphoma [NHL] and cervical cancer) as well as non-AIDS-defining cancers in the 2 years after AIDS onset. For each cancer, the change in SIRs across CD4 counts (0-49 cells/mm3, 50-99 cells/mm3, 100-199 cells/mm3, and > or =200 cells/mm3) was modeled using Poisson regression.

RESULTS

The SIRs for KS, NHL, and cervical cancer were 258, 78, and 8.8, respectively. For each fall of 100 CD4 cells/mm3, RRs were 1.36 (95% CI: 1.29-1.43) for KS and 1.48 (95% CI: 1.37-1.59) for NHL. Among NHL subtypes, the association with lower CD4 counts was strongest for immunoblastic lymphoma (RR =1.64, 95% CI: 1.37-1.96, per decline of 100 CD4 cells/mm3) and central nervous system lymphoma (RR = 2.29, 95% CI: 1.95-2.69). The SIR for cervical cancer did not vary with CD4 count (p =.74). For non-AIDS-defining cancers (overall SIR = 2.1), neither the combined risk nor the risk of specific types was associated with declining CD4 counts.

CONCLUSION

SKS and NHL risk increased with level of immunosuppression at AIDS onset. Risks for other cancers, including cervical cancer, were unrelated to CD4 counts. Elevated risks for non-AIDS cancers may be a result of lifestyle factors.

Gene expression profile of AIDS-related Kaposi's sarcoma

BACKGROUND

Kaposi's Sarcoma (KS) is a proliferation of aberrant vascular structures lined by spindle cells, and is caused by a gammaherpes virus (HHV8/KSHV). Its course is aggravated by co-infection with HIV-1, where the timing of infection with HIV-1 and HHV8 is important for the clinical outcome.

METHODS

In order to better understand the pathogenesis of KS, we have analysed tissue from two AIDS-KS lesions, and from normal skin by serial analysis of gene expression (SAGE). Semi-quantitative RT-PCR was then used to validate the results.

RESULTS

The expression profile of AIDS-related KS (AIDS-KS) reflects an active process in the skin. Transcripts of HHV8 were found to be very low, and HIV-1 mRNA was not detected by SAGE, although it could be found using RT-PCR. Comparing the expression profile of AIDS-KS tissue with publicly available SAGE libraries suggested that AIDS-KS mRNA levels are most similar to those in an artificially mixed library of endothelial cells and leukocytes, in line with the description of KS lesions as containing spindle cells with endothelial characteristics, and an inflammatory infiltrate. At least 64 transcripts were found to be significantly elevated, and 28 were statistically downregulated in AIDS-KS compared to normal skin. Five of the upregulated mRNAs, including Tie 1 and sialoadhesin/CD169, were confirmed by semi-quantitative PCR to be elevated in additional AIDS-KS biopsies. Antibodies to sialoadhesin/CD169, a known marker of activated macrophages, were shown to specifically label tumour macrophages.

CONCLUSION

The expression profile of AIDS-KS showed 64 genes to be significantly upregulated, and 28 genes downregulated, compared with normal skin. One of the genes with increased expression was sialoadhesin (CD169). Antibodies to sialoadhesin/CD169 specifically labelled tumour-associated macrophages, suggesting that macrophages present in AIDS-KS lesions belong to a subset of human CD169+ macrophages.

Viral versus cellular BCL-2 proteins

All gamma herpesviruses and a few other viruses encode at least one homologue of the mammalian cell death inhibitor BCL-2. Gamma herpesviruses are associated with human and animal lymphoid and epithelial tumours. However, the role of these viral BCL-2 homologues in the virus replication cycle or in human disease is not known, though recent developments show progress in this area. The structure of viral BCL-2 family protein, KSBcl-2, is similar to that of cellular family members, but viral BCL-2 proteins differ functionally from the cellular proteins, apparently escaping the regulatory mechanisms to which their cellular counterparts are subjected. Thus, exploring the biochemical and biological functions of the viral BCL-2 family proteins will increase our understanding of their role in virus infections and will undoubtedly teach us something about their cellular kin.

Integrin alpha(v)beta3 targeted therapy for Kaposi's sarcoma with an in vitro evolved antibody

Here, we define integrin alpha(v)beta3 as a molecular target for antibody therapy for Kaposi's sarcoma (KS). We previously reported, using a new phage display strategy based on designed combinatorial V gene libraries, the humanization of mouse monoclonal antibody LM609 directed to human integrin alpha(v)beta3. In the present study, we describe the in vitro affinity maturation of humanized LM609 by using a phage display strategy for the sequential and parallel optimization of three complementarity determining regions of the antibody molecule. The evolved Fab had an affinity of 150 pM and was converted into IgG1 by use of a new mammalian expression vector. The resulting whole antibody, designated JC-7U IgG1, was found to selectively target human KS in a nude mouse model and inhibit tumor growth at a therapeutically relevant dose. Because of its high affinity and its high degree of humanization, JC-7U IgG1 is an excellent drug candidate for therapeutic applications that involve integrin alpha(v)beta3 as the molecular target. Of particular interest is therapy for KS, breast cancer, melanoma, and other cancers in which integrin alpha(v)beta3 is expressed on both angiogenic endothelial cells and tumor cells, which would allow a dual antiangiogenic and antitumor strike with a single drug.

Guanylate-binding protein-1 expression is selectively induced by inflammatory cytokines and is an activation marker of endothelial cells during inflammatory diseases

During angiogenesis and inflammatory processes, endothelial cells acquire different activation phenotypes, whose identification may help in understanding the complex network of angiogenic and inflammatory interactions in vivo. To this goal we investigated the expression of the human guanylate-binding protein (GBP)-1 that is highly induced by inflammatory cytokines (ICs) and, therefore, may characterize IC-activated cells. Using a new rat monoclonal antibody raised against GBP-1, we show that GBP-1 is a cytoplasmic protein and that its expression in endothelial cells is selectively induced by interferon-gamma, interleukin-1alpha, interleukin-1beta, or tumor necrosis factor-alpha, but not by other cytokines, chemokines, or growth factors. Moreover, we found that GBP-1 expression is highly associated with vascular endothelial cells as confirmed by the simultaneous detection of GBP-1 and the endothelial cell-associated marker CD31 in a broad range of human tissues. Notably, GBP-1 expression was undetectable in the skin, but it was highly induced in vessels of skin diseases with a high-inflammatory component including psoriasis, adverse drug reactions, and Kaposi's sarcoma. These results indicate that GBP-1 is a novel cellular activation marker that characterizes the IC-activated phenotype of endothelial cells.

Removal of T and B lymphocytes by in-line filtration: evaluation of the efficiency of a polyester filter type (Pall WBF-2) by flow cytometric counting

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate whether in-line filtration, using a polyester filter for the preparation of red cell concentrates (RCC) and plasma (PL), leads to an altered proportion of T and B lymphocytes in the fraction of residual white blood cells (WBC).

MATERIALS AND METHODS

The capacity of Pall WBF-2 in-line filters to reduce the numbers of T and B lymphocytes from red blood cell concentrates (RCC) and plasma (PL) of 22 donations was investigated by three-colour flow cytometry (FC) using the Tritest-Trucount kit. T and B lymphocytes were identified using monoclonal antibodies (mAbs) against CD3, CD19 and CD45, conjugated with fluorescein isothiocyanate, phycoerythrin or peridinin chlorophyll protein-A, respectively. As the number of B cells was below the detection limit of the FC method, WBC of the respective blood components of healthy donors were concentrated 25-fold by Percoll density-gradient centrifugation. In this fraction the absolute numbers of T and B cells, as well as their ratio, were determined using the Attractor software, which provides a discrimination of rare cell counts from FC in relation to debris.

RESULTS

The mean numbers, as well as minima and maxima of T and B lymphocytes per unit, were as follows. T cells in RCC: 4.51 x 10(3) (1.68 x 10(2)-4.09 x 10(4)) and in PL: 1.35 x 10(3) (2.21-1.78 x 10(4)); B cells in RCC: 2.33 x 10(3) (7.10 x 10(1)-9.15 x 10(3)) and in PL: 2.33 x 102 (7.5 x 10(2)-2.8 x 10(3)). T cells were retained, on average, at a higher level than B cells: 3.01 times higher in RCC and 1.01 times higher in PL.

CONCLUSION

After filtration, the ratio of T and B lymphocytes changed in RCC (1.95 : 1) compared with unfiltered blood, where it was 5.83 : 1. In PL the ratio did not change notably compared to unfiltered blood. The results of this research show that cell concentration (using gradient centrifugation) in combination with an appropriate FC acquisition and analysis procedure, allows both residual T and B lymphocytes (being under the detection limit without cell concentration) to be determined.

Body cavity lymphoma

Body cavity lymphomas (BCLs) are a heterogeneous group of rare, primary non-Hodgkin's lymphomas that proliferate within the serous body cavities and result in recurrent effusions. This review is mainly focussed on the distinct entity primary effusion lymphoma (PEL) wherein the tumor clone is infected by human herpesvirus-8, the etiologic agent of Kaposi's sarcoma. In addition, we briefly discuss here recent data regarding other BCL types. The latter include a subset with no evidence of herpesvirus 8 which is associated with Epstein-Barr virus (pyothorax-associated lymphoma, PAL), the BCL forms associated to hepatitis C virus-related cirrhosis or alcohol-related cirrhosis and, finally, non-neoplastic forms mimicking lymphomatous effusions.

Kaposi's sarcoma-associated herpesvirus OX2 glycoprotein activates myeloid-lineage cells to induce inflammatory cytokine production

Kaposi's sarcoma is an inflammatory cytokine-mediated angioproliferative disease which is triggered by infection by Kaposi's sarcoma-associated herpesvirus (KSHV). KSHV contains an open reading frame, K14, that has significant homology with cellular OX2, designated viral OX2 (vOX2). In this report, we demonstrate that vOX2 encodes a glycosylated cell surface protein with an apparent molecular mass of 55 kDa. Purified glycosylated vOX2 protein dramatically stimulated primary monocytes, macrophages, and dendritic cells to produce the inflammatory cytokines interleukin 1beta (IL-1beta), IL-6, monocyte chemoattractant protein 1, and TNF-alpha. Furthermore, expression of vOX2 on B lymphocytes stimulated monocytes to produce inflammatory cytokines in mixed culture. These results demonstrate that like its cellular counterpart, vOX2 targets myeloid-lineage cells, but unlike cellular OX2, which delivers a restrictive signal, KSHV vOX2 provides an activating signal, resulting in the production of inflammatory cytokines. Thus, this is a novel viral strategy where KSHV has acquired the cellular OX2 gene to induce inflammatory cytokine production, which potentially promotes the cytokine-mediated angiogenic proliferation of KSHV-infected cells.

Mechanistic aspects of HIV-1 reverse transcription initiation

During reverse transcription, the positive-strand HIV-1 RNA genome is converted into a double-stranded DNA copy which can be permanently integrated into the host cell genome. Recent analyses show that HIV-1 reverse transcription is a highly regulated process. The initiation reaction can be distinguished from a subsequent elongation reaction carried out by a reverse transcription complex composed of (at least) heterodimeric reverse transcriptase, cellular tRNA(lys3) and HIV-1 genomic RNA sequences. In addition, viral factors including Tat, Nef, Vif, Vpr, IN and NCp7, cellular proteins, and TAR RNA and other RNA stem-loop structures appear to influence this complex and contribute to the efficiency of the initiation reaction. As viral resistance to many antiretroviral compounds is a continuing problem, understanding the ways in which these factors influence the reverse transcription complex will likely lead to novel antiretroviral strategies.

The emerging role of the human herpesvirus 8 (HHV8) in human neoplasia

The human herpesvirus 8 (HHV8) was initially described and characterised in Kaposi's sarcoma tissue. The virus was found in the lesion of most cases of Kaposi's sarcoma. Whilst there is a large body of evidence to implicate its role in the pathogenesis of Kaposi's sarcoma, it has recently been found that the virus may also be important in a number of other human neoplasias. This review will examine the molecular pathology of HHV8 in the pathogenesis of Kaposi's sarcoma and summarise the current evidence and postulated mechanisms in its role in other human neoplasias.

The helical domain of GBP-1 mediates the inhibition of endothelial cell proliferation by inflammatory cytokines

Inflammatory cytokines (IC) activate endothelial cell adhesiveness for monocytes and inhibit endothelial cell growth. Here we report the identification of the human guanylate binding protein-1 (GBP-1) as the key and specific mediator of the anti-proliferative effect of IC on endothelial cells. GBP-1 expression was induced by IC, downregulated by angiogenic growth factors, and inversely related to cell proliferation both in vitro in microvascular and macrovascular endothelial cells and in vivo in vessel endothelial cells of Kaposi's sarcoma. Experimental modulation of GBP-1 expression demonstrated that GBP-1 mediates selectively the anti-proliferative effect of IC, without affecting endothelial cell adhesiveness for monocytes. GBP-1 anti-proliferative activity did not affect ERK-1/2 activation, occurred in the absence of apoptosis, was found to be independent of the GTPase activity and isoprenylation of the molecule, but was specifically mediated by the C-terminal helical domain of the protein. These results define GBP-1 as an important tool for dissection of the complex activity of IC on endothelial cells, and detection and specific modulation of the IC-activated non-proliferating phenotype of endothelial cells in vascular diseases.