Shou-Jiang Gao

Seroconversion to Antibodies against Kaposi's Sarcoma–Associated Herpesvirus–Related Latent Nuclear Antigens before the Development of Kaposi's Sarcoma

BACKGROUND If Kaposis sarcoma-associated herpesvirus (KSHV) is the cause of Kaposis sarcoma, serologic evidence of infection should be present in patients before the disease develops. METHODS Using an immunoblot assay for two latent nuclear antigens of KSHV, we tested serum samples from homosexual male patients with the acquired immunodeficiency syndrome (AIDS) with and without Kaposis sarcoma (HIV-infected men with hemophilia), HIV-seronegative blood donors, and HIV-seronegative patients with high titers of antibodies against Epstein-Barr virus (EBV). Serial serum samples obtained from patients with Kaposis sarcoma before the diagnosis of the disease were tested for evidence of seroconversion. RESULTS Of 40 patients with Kaposis sarcoma, 32 (80 percent) were positive for antibodies against KSHV antigens by the immunoblot assay, as compared with only 7 of 40 homosexual men (18 percent) without Kaposis sarcoma immediately before the onset of AIDS. Of 122 blood donors, 22 EBV-infected patients, and 20 HIV-infected men with hemophilia, none were seropositive. When studied by the immunoblot assay over a period of 13 to 103 months, 21 of the 40 patients with Kaposis sarcoma (52 percent) seroconverted 6 to 75 months before the clinical appearance of Kaposis sarcoma. The median duration of antibody seropositivity for KSHV-related latent nuclear antigens before the diagnosis of Kaposis sarcoma was 33 months. CONCLUSIONS In most patients with kaposis sarcoma and AIDS, seroconversion to positivity for antibodies against KSHV-related nuclear antigens occurs before the clinical appearance of Kaposis sarcoma. This supports the hypothesis that Kaposis sarcoma results from infection with KSHV.

KSHV ORF K9 (vIRF) is an oncogene which inhibits the interferon signaling pathway

Kaposis sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus linked to the development of Kaposis sarcoma and a rare B cell lymphoma, primary effusion lymphoma. The KSHV gene ORF K9 encodes vIRF which is a protein with low but significant homology to members of the interferon (IFN) regulatory factor (IRF) family responsible for regulating intracellular interferon signal transduction (Moore PS, Boshoff C, Weiss RA and Chang Y. (1996). Science, 274, 1739 – 1744). vIRF inhibits IFN-β signal transduction as measured using an IFN-responsive ISG54 reporter construct co-transfected with ORF K9 into HeLa and 293 cells. vIRF also suppresses genes under IFN regulatory control as shown by inhibition of the IFN-β inducibility of p21WAF1/CIP1, however, no direct DNA-binding or protein-protein interactions characteristic for IRF repressor proteins were identified. Stable transfectant NIH3T3 clones expressing vIRF grew in soft agar and at low serum concentrations, lost contact inhibition and formed tumors after injection into nude mice indicating that vIRF has the properties of a viral oncogene. Since vIRF is primarily expressed in KSHV-infected B cells, not KS spindle cells, this study suggests that vIRF is a transforming oncogene active in B cell neoplasias that may provide a unique immune escape mechanism for infected cells. This data is consistent with tumor suppressor pathways serving a dual function as host cell antiviral pathways.

Antibodies to Butyrate-Inducible Antigens of Kaposi's Sarcoma–Associated Herpesvirus in Patients with HIV-1 Infection

BACKGROUND The recent identification in patients with Kaposis sarcoma of DNA sequences with homology to gammaherpesviruses has led to the hypothesis that a newly identified virus, Kaposis sarcoma-associated herpeslike virus (KSHV), has a role in the pathogenesis of Kaposis sarcoma. We developed serologic markers for KSHV infection. METHODS KSHV antigens were prepared from a cell line (BC-1) that contains the genomes of both KSHV and the Epstein-Barr virus (EBV). We used immunoblot and immunofluorescence assays to examine serum samples from 102 patients with human immunodeficiency virus type 1 (HIV-1) infection for antibodies to KSHV-associated proteins and to distinguish these antibodies from antibodies to EBV antigens. A positive serologic response was defined by the recognition of an antigenic polypeptide, p40, in n-butyrate-treated BC-1 cells and by the absence of p40 recognition in untreated BC-1 cells or EBV-infected, KSHV-negative cells. The detection by the immunofluorescence assay of 10 to 20 times more antigen-positive cells in n-butyrate-treated BC-1 cells than in untreated cells was considered a positive response. RESULTS Antibodies to the p40 antigen expressed by chemically treated BC-1 cells were identified in 32 of 48 HIV-1-infected patients with Kaposis sarcoma (67 percent), as compared with only 7 of 54 HIV-1-infected patients without Kaposis sarcoma (13 percent). These results were confirmed by an immunofluorescence assay. The positive predictive value of the serologic tests for Kaposis sarcoma was 82 percent, and the negative predictive value 75 percent. CONCLUSIONS The presence of antibodies to a KSHV antigenic peptide correlates with the presence of Kaposis sarcoma in a high-risk population and provides further evidence of an etiologic role for KSHV.