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

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Abstract
The recent identification in patients with Kaposi's sarcoma of DNA sequences with homology to gammaherpesviruses has led to the hypothesis that a newly identified virus, Kaposi's sarcoma–associated herpeslike virus (KSHV), has a role in the pathogenesis of Kaposi's sarcoma. We developed serologic markers for KSHV infection. 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. Antibodies to the p40 antigen expressed by chemically treated BC-1 cells were identified in 32 of 48 HIV-1–infected patients with Kaposi's sarcoma (67 percent), as compared with only 7 of 54 HIV-1–infected patients without Kaposi's sarcoma (13 percent). These results were confirmed by an immunofluorescence assay. The positive predictive value of the serologic tests for Kaposi's sarcoma was 82 percent, and the negative predictive value 75 percent. The presence of antibodies to a KSHV antigenic peptide correlates with the presence of Kaposi's sarcoma in a high-risk population and provides further evidence of an etiologic role for KSHV.