Kaposi's sarcoma-associated herpesvirus inhibits expression and function of endothelial cell major histocompatibility complex class II via suppressor of cytokine signaling 3.

Endothelial cells (EC) can present antigen to either CD8(+) T lymphocytes through constitutively expressed major histocompatibility complex class I (MHC-I) or CD4(+) T lymphocytes through gamma interferon (IFN-γ)-induced MHC-II. Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS), an EC neoplasm characterized by dysregulated angiogenesis and a substantial inflammatory infiltrate. KSHV is understood to have evolved strategies to inhibit MHC-I expression on EC and MHC-II expression on primary effusion lymphoma cells, but its effects on EC MHC-II expression are unknown. Here, we report that the KSHV infection of human primary EC inhibits IFN-γ-induced expression of the MHC-II molecule HLA-DR at the transcriptional level. The effect is functionally significant, since recognition by an HLA-DR-restricted CD4(+) T-cell clone in response to cognate antigen presented by KSHV-infected EC was attenuated. Inhibition of HLA-DR expression was also achieved by exposing EC to supernatant from KSHV-inoculated EC before IFN-γ treatment, revealing a role for soluble mediators. IFN-γ-induced phosphorylation of STAT-1 and transcription of CIITA were suppressed in KSHV-inoculated EC via a mechanism involving SOCS3 (suppressor of cytokine signaling 3). Thus, KSHV infection resulted in transcriptional upregulation of SOCS3, and treatment with RNA interference against SOCS3 relieved virus-induced inhibition of IFN-γ-induced STAT-1 phosphorylation. Since cell surface MHC-II molecules present peptide antigens to CD4(+) T lymphocytes that can function either as direct cytolytic effectors or to initiate and regulate adaptive immune responses, inhibition of this antigen-presenting pathway would provide a survival advantage to the virus.

Kaposi's sarcoma-associated herpesvirus viral interferon regulatory factor-2 inhibits type 1 interferon signalling by targeting interferon-stimulated gene factor-3.

Kaposi's sarcoma-associated herpesvirus (KSHV) encodes four viral interferon regulatory factors (vIRF-1-4). We investigated the mechanism and consequences of vIRF-2-mediated inhibition of interferon-response element signalling following type I interferon (IFN) induction. Western blot and electrophoretic mobility-shift assays identified the interferon-stimulated gene factor-3 (ISGF-3) components STAT1 and IRF-9 as the proximal targets of vIRF-2 activity. The biological significance of vIRF-2 inhibition of ISGF-3 was demonstrated by vIRF-2-mediated rescue of the replication of the IFN-sensitive virus encephalomyocarditis virus. This study provides both a mechanism and evidence for KSHV vIRF-2-mediated suppression of the consequences of type 1 IFN-induced signalling.

Kaposi's sarcoma-associated herpesvirus infection of endothelial cells inhibits neutrophil recruitment through an interleukin-6-dependent mechanism: a new paradigm for viral immune evasion.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS), an endothelial cell (EC) neoplasm characterized by dysregulated angiogenesis and inflammation. KSHV infection of EC causes production of proinflammatory mediators, regarded as possible initiators of the substantial mononuclear leukocyte recruitment seen in KS. Conversely, KSHV immune evasion strategies exist, such as degradation of EC leukocyte adhesion receptors by viral proteins. Here, we report the effects of KSHV infection of primary EC on recruitment of flowing leukocytes. Infection did not initiate adhesion of any leukocyte subset per se. However, on cytokine-stimulated EC, KSHV specifically inhibited neutrophil, but not PBL or monocyte, transmigration, an observation consistent with the inflammatory cell profile found in KS lesions in vivo. This inhibition could be recapitulated on uninfected EC using supernatant from infected cultures. These supernatants contained elevated levels of human interleukin 6 (hIL-6), and both the KSHV- and the supernatant-induced inhibitions of neutrophil transmigration were abrogated in the presence of a hIL-6 neutralizing antibody. Furthermore, preconditioning of EC with hIL-6 mimicked the effect of KSHV. Using RNA interference (RNAi), we show that upregulation of suppressor of cytokine signaling 3 (SOCS3) was necessary for this effect of hIL-6. These studies reveal a novel paracrine mode of KSHV immune evasion, resulting in reduced recruitment of neutrophils, a cell type whose antiviral and antitumor roles are becoming increasingly appreciated. Moreover, the findings have implications for our understanding of the contribution of hIL-6 to the pathogenesis of other inflammatory disorders and tumors in which this cytokine is abundant.

Dissecting the regions of virion-associated Kaposi's sarcoma-associated herpesvirus complement control protein required for complement regulation and cell binding.

Complement, which bridges innate and adaptive immune responses as well as humoral and cell-mediated immunity, is antiviral. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a lytic cycle protein called KSHV complement control protein (KCP) that inhibits activation of the complement cascade. It does so by regulating C3 convertases, accelerating their decay, and acting as a cofactor for factor I degradation of C4b and C3b, two components of the C3 and C5 convertases. These complement regulatory activities require the short consensus repeat (SCR) motifs, of which KCP has four (SCRs 1 to 4). We found that in addition to KCP being expressed on the surfaces of experimentally infected endothelial cells, it is associated with the envelope of purified KSHV virions, potentially protecting them from complement-mediated immunity. Furthermore, recombinant KCP binds heparin, an analogue of the known KSHV cell attachment receptor heparan sulfate, facilitating infection. Treating virus with an anti-KCP monoclonal antibody (MAb), BSF8, inhibited KSHV infection of cells by 35%. Epitope mapping of MAb BSF8 revealed that it binds within SCR domains 1 and 2, also the region of the protein involved in heparin binding. This MAb strongly inhibited classical C3 convertase decay acceleration by KCP and cofactor activity for C4b cleavage but not C3b cleavage. Our data suggest similar topological requirements for cell binding by KSHV, heparin binding, and regulation of C4b-containing C3 convertases but not for factor I-mediated cleavage of C3b. Importantly, they suggest KCP confers at least two functions on the virion: cell binding with concomitant infection and immune evasion.

Immune responses in baboons vaccinated with HIV-2 genetic expression libraries.

Immunization using genetic expression libraries may be an improvement over conventional DNA immunization using a single gene because more epitopes are simultaneously presented to the immune system. In this study, we evaluated the effectiveness of an HIV-2 vaccine made from a genomic expression library in baboons. We found that HIV-2 expression library immunization induced HIV-2-specific memory responses but low levels of CD8+ cell anti-viral responses and neutralizing antibodies. After intravenous virus challenge using a homologous pathogenic variant, HIV-2UC2/9429, viral loads were similar in the HIV-2-immunized and control baboons. We conclude that although immunization using HIV-2 expression libraries induces immune responses, this approach does not provide protection in baboons against intravenous challenge with HIV-2.

The restricted cellular host range of human herpesvirus 8.

DESIGN: A selection of primary and transformed cell types were evaluated for their susceptibility to infection with human herpesvirus 8 (HHV-8)/Kaposi's sarcoma-associated herpesvirus. METHODS: Sources of HHV-8 included Kaposi's sarcoma lesion punch biopsies that were either cocultured directly with target cells or that were first cocultured with human lymphocytes to derive HHV-8-containing fluids that were inoculated onto target cells. HHV-8 was also obtained from primary effusion lymphoma-derived cell lines. Techniques to detect infection included the PCR, immunofluorescence assays and in situ hybridization. RESULTS: Susceptible cells included human umbilical cord blood mononuclear cells (UCMC), adult CD19 B cells, macrophages and certain endothelial cells of human and animal origin, including some that are transformed with human papilloma virus type 16 E6 and E7 genes. The infection of lymphocytes did not yield established lymphoblastoid cell lines (LCL) and virus infection persisted for only 4-7 days. However, long-term HHV-8 infection of UCMC could be achieved by coinfection with Epstein-Barr virus. HHV-8 could also infect UCMC LCL recently derived by Epstein-Barr virus transformation, but long-established LCL could not be infected with HHV-8. CONCLUSIONS: These data provide further biological evidence in cell culture for the limited cellular host range of HHV-8 to CD19 B cells, macrophages, and certain endothelial cells.

Suppression of human immunodeficiency virus type 1 replication by a soluble factor produced by CD8+ lymphocytes from HIV-2-infected baboons.

Human immunodeficiency virus type 2 (HIV-2)-infected baboons (Papio cynocephalus) provide a valuable animal model for the study of acquired immunodefidency syndrome (AIDS) pathogenesis since many features of disease progression resemble HIV-1-infection of humans. In some HIV-2-infected baboons that are clinically healthy, a CD8+ cell antiviral response, that is partly mediated by a soluble factor, controls viral replication in vitro. In the present study, we demonstrate that CD8+ cells derived from HIV-2-infected baboon peripheral blood, lymph nodes, adenoids and tonsils had antiviral activity in co-cultures of CD8+ and CD4+ cells that inversely correlates with viral load. A soluble factor was found to be active against the chemokine-resistant, syncytium-inducing HIV-1SF2 and HIV-1SF33 isolates and was relatively heat stable at 100 degrees C for 10 min. Moreover, inhibition of the transcription from the long terminal repeat of HIV-1 was observed in 1G5 cells after activation with phorbol 12-myristate 13-acetate. Therefore, the soluble suppressing activity of CD8+ cells in HIV-2-infected baboons may be analogous to the CD8+ cell antiviral factor described in human HIV-infected asymptomatic people.

Increased human herpesvirus 8 seroprevalence in young homosexual men who have multiple sex contacts with different partners.

The objective of this study was to evaluate the behavioral risks that are associated with human herpesvirus 8 (HHV-8) infection in a cohort of young homosexual men. Seventy-nine subjects (ages 22-33 years) who completed a questionnaire about their sexual and drug use behavior over the preceding year were recruited from the San Francisco Young Men's Health Study. Plasma samples were tested for anti-HHV-8 antibodies using an indirect IFA. Thirty-eight subjects (48.1%) were infected with HHV-8. HHV-8 infection was significantly linked to an increasing number of male sex partners (P=.025, Mantel-Haenszel chi2 test for trend), suggesting a strong association between HHV-8 infection and multiple homosexual contacts.

Human immunodeficiency virus-2 infection in baboons is an animal model for human immunodeficiency virus pathogenesis in humans.

OBJECTIVE: To assess disease progression in baboons (Papio cynocephalus) that were infected with two human immunodeficiency virus-2 (HIV-2) isolates. METHODS: Eight baboons were inoculated intravenously with either HIV-2UC2 or HIV-2UC14 and were followed for a 2- to 7-year period of observation. RESULTS: Six of 8 baboons showed lymphadenopathy and other signs of HIV-related disease, 3 of 8 baboons had an acute phase CD4+ T-cell decline, and 2 of 5 baboons infected with the HIV-2UC2 isolate progressed to an acquired immunodeficiency syndrome-like disease. Human immunodeficiency virus-2-specific pathology in lymphatic tissues included follicular lysis, vascular proliferation, and lymphoid depletion. Both neutralizing antibodies and a CD8+ T-cell antiviral response were associated with resistance to disease. CONCLUSIONS: Disease progression and the development of acquired immunodeficiency syndrome in HIV-2-infected baboons have similarities to human HIV infections.

Transient virus infection and pathogenesis of a new HIV type 2 isolate, UC12, in baboons.

We have previously shown that baboons (Papio cynocephalus) can be persistently infected with HIV-2 and some baboons progress to an AIDS-like disease with a CD4+ T cell decline, cachexia, alopecia, and Kaposi's sarcoma-like fibromatosis. In this study, we found that a new virus isolate, HIV-2UC12, replicated to high levels in baboon peripheral blood mononuclear cells (PBMCs) in vitro. Three baboons were subsequently inoculated and had plasma viral RNA loads that peaked between 15,000 and 7000 copies/ml at 2 weeks postinfection. Virus was isolated from the PBMCs for up to 6 months. Although PBMCs were subsequently virus culture negative, virus could be recovered from the spleen, lymph nodes, and tonsils, indicating that HIV-2 was sequestered within these lymphoid tissues. HIV-2-associated pathology included follicular lysis, vascular proliferation, and lymphoid depletion. This study indicated that HIV-2UC12 infection in baboons can cause HIV-associated pathological abnormalities within the lymphatic tissues and that the high level of HIV-2UC12 replication in vitro was not predictive of replication in vivo.

CD8 cell noncytotoxic antiviral activity in human immunodeficiency virus-infected and -uninfected children.

CD8 cells from human immunodeficiency virus (HIV)-infected adults and children can show cytotoxic as well as noncytotoxic activity against viral replication. The noncytotoxic anti-HIV response, measured by suppression of acute viral infection of CD4 cells, has also been observed in uninfected adults who have a history of exposure to HIV. This CD8 cell antiviral activity was found to be detectable as well in approximately 50% of uninfected children born of infected mothers. The findings could reflect a protective response of the children to HIV after being exposed to the virus.

Human herpesvirus 8 detection in nasal secretions and saliva.

The presence of human herpesvirus 8 (HHV-8) was determined by polymerase chain reaction (PCR) in nasal secretions and saliva from 14 HHV-8-seropositive persons, including 8 Kaposi's sarcoma patients: 7 were human immunodeficiency virus type 1-infected, 6 of whom were asymptomatic. HHV-8 was detected in one or both body fluids in 8 (57%) of 14 subjects. Parallel PCR testing revealed the concomitant presence of cytomegalovirus, Epstein-Barr virus, and HHV-6 in various combinations in these body fluids. These data indicate frequent shedding of multiple herpesviruses in nasal secretions and saliva, particularly in Kaposi's sarcoma patients. Both body fluids are therefore potential sources HHV-8 by nonsexual transmission.

Superinfection with human immunodeficiency virus type 2 can reactivate virus production in baboons but is contained by a CD8 T cell antiviral response.

An animal model was used to assess whether resistance to superinfection by human immunodeficiency virus (HIV) can exist in vivo. Asymptomatic baboons (Papio cynocephalus), previously infected with HIV-2, were first challenged with homologous virus (HIV-2UC2 or HIV-2UC14) and later with heterologous virus (HIV-2UC12). After both virus inoculations, either resistance to viral infection or a transient viremia was observed. The original virus was recovered in 3 baboons, suggesting that reactivation of a latent infection occurred on heterologous challenge and that HIV-2 superinfection is blocked by processes established during prior infection. Antibody titers measured by ELISA and virus neutralization remained at low levels. However, suppression of HIV-1 replication was observed with CD8 T cells and filtered cell culture supernatants. The soluble factor involved was not a beta-chemokine. This resistance to HIV superinfection appears to be mediated at least in part by CD8 T cells that suppress virus production.

CD8+ cells from HIV-2-infected baboons control HIV replication.

OBJECTIVE: To analyze the CD8+ cell antiviral immune response in HIV-2-infected baboons. DESIGN: Baboons were infected with clinical isolates of HIV-2, CD8+ cells were isolated from phytohemagglutinin (PHA)-stimulated baboon peripheral blood mononuclear cells (PBMC). These cells were cultured with PHA-stimulated CD4+ cells acutely infected with HIV-2 at several CD8+:CD4+ cell ratios. Control of HIV-2 replication was determined by comparing peak levels of HIV-2 replication in fluids from CD8+:CD4+ cell cocultures with those in fluids from infected CD4+ cells cultured alone. RESULTS: CD8+ cells from HIV-2-infected baboons inhibited HIV-2 replication in acutely infected autologous CD4+ cells to a significantly greater extent than did CD8+ cells from uninfected baboons (P = 0.0001). At the beginning of the acute phase of HIV-2 infection, CD8+ cells showed either a transient reduction or loss in the antiviral activity. In some cases the CD8+ cell response enhanced HIV-2 replication. Subsequently, the strength of the CD8+ cell antiviral activity increased concomitant with a decrease in the HIV-2 load in the PBMC. Suppression of HIV replication could be demonstrated with filtered fluid from CD8+ cells. Other studies indicated that infected CD4+ cells are lost during coculture of CD8+ cells with infected CD4+ cells. CONCLUSIONS: CD8+ cells of HIV-2-infected baboons develop substantial anti-HIV-2 activity following HIV-2 infection, which may account in part for the low frequency of pathogenesis in HIV-2-infected baboons. Studies to elucidate the mechanism of this CD8+ cell antiviral activity suggest that it is mediated in part by a soluble antiviral factor, but primarily in association with the loss of infected CD4+ cells.

Infectious human herpesvirus 8 in a healthy North American blood donor.

BACKGROUND: Molecular studies have provided strong evidence for the association of human herpesvirus 8 (HHV-8) with Kaposi's sarcoma. These data have been supported by serological studies, which have also suggested that HHV-8 can be found in the healthy population. We report the presence of infectious HHV-8 in a healthy donor to a North American blood bank. METHODS: We examined the peripheral blood mononuclear cells or CD19 cells of blood donors by PCR for evidence of HHV-8 infection. The CD19 cells were separated from peripheral blood mononuclear cells by immunomagnetic-bead selection. To enhance detection of HHV-8, the CD19 cells from eleven unsystematically selected blood donors were activated with phorbol ester and recombinant interleukin-6; the culture fluid was filtered and inoculated onto HHV-8-negative target CD19 cells that had been prepared from phytohaemagglutinin-stimulated peripheral blood mononuclear cells. These inoculated target cells were cultured for 3 days and then analysed for HHV-8 sequences by PCR. Serum samples were tested for antibodies to HHV-8 by an indirect immunofluorescence assay. FINDINGS: One blood donor was consistently found to be infected with HHV-8 by PCR after the cell-culture activation procedure. He was seropositive for the virus. The HHV-8 recovered was infectious, as shown by a reverse-transcription-PCR technique that detected HHV-8 RNA in the inoculated target cells. INTERPRETATION: These data provide the first indication that HHV-8 can be recovered from the blood of a healthy individual, a blood donor, and that the virus is infectious. This observation suggests that HHV-8 could be transmitted by blood transfusion, a possibility that merits further study.

Suppression of HIV replication by lymphoid tissue CD8+ cells correlates with the clinical state of HIV-infected individuals.

Lymphoid tissues from asymptomatic HIV-infected individuals, as compared with symptomatic HIV-infected subjects, show limited histopathological changes and lower levels of HIV expression. In this report we correlate the control of HIV replication in lymph nodes to the non-cytolytic anti-HIV activity of lymphoid tissue CD8+ cells. Five subjects at different stages of HIV-related disease were studied and the ability of their CD8+ cells, isolated from both lymphoid tissue and peripheral blood, to inhibit HIV replication was compared. CD8+ cells from lymphoid tissue and peripheral blood of two HIV-infected long-term survivors suppressed HIV replication at a low CD8+:CD4+ cell ratio of 0.1. The CD8+ cells from the lymphoid tissue of a third asymptomatic subject suppressed HIV replication at a CD8+:CD4+ cell ratio of 0.25; the subject's peripheral blood CD8+ cells showed this antiviral response at a lower ratio of 0.05. The lymphoid tissue CD8+ cells from two AIDS patients were not able to suppress HIV replication, and the peripheral blood CD8+ cells of only one of them suppressed HIV replication. The plasma viremia, cellular HIV load as well as the extent of pathology and virus expression in the lymphoid tissue of the two long-term survivors, were reduced compared with these parameters in the three other subjects. The data suggest that the extent of anti-HIV activity by CD8+ cells from lymphoid tissue relative to peripheral blood correlates best with the clinical state measured by lymphoid tissue pathology and HIV burden in lymphoid tissues and blood. The results add further emphasis to the importance of this cellular immune response in controlling HIV pathogenesis.

Antibodies to human herpesvirus type 8 in the general population and in Kaposi's sarcoma patients.

BACKGROUND: Much of the evidence that human herpesvirus type 8 (HHV-8) is associated with Kaposi's sarcoma (KS) has come from molecular studies of HHV-8 DNA. Seroepidemiological studies have been hampered by the lack of a reliable assay. METHODS: The serological data reported here were obtained by means of a mouse monoclonal antibody-enhanced immunofluorescence assay for antibodies to lytic and latent HHV-8 antigens. 1435 single samples of serum (or plasma) from many different disease groups and parts of the world were assayed. FINDINGS: All patients with African endemic KS and 96% of American patients with AIDS-associated KS were seropositive for lytic antigen, as were 90% of American HIV-infected homosexual men; by contrast only 23% of HIV-seropositive drug users and 21% of HIV-seropositive women were positive for HHV-8 antibody. Factor VIII treatment before 1983 did not increase the risk of HHV-8 infection in patients with haemophilia. In the American general population, about 25% of adults (including volunteer blood donors) and 2-8% of children had antibodies to HHV-8. INTERPRETATION: Our data are consistent with HHV-8 being primarily associated with sexual transmission, but the HHV-8 seropositivity rate in American children suggests that there is a non-sexual route of HHV-8 infection also. On the evidence available so far, the risk of parenteral transmission is low.