IDENTIFICATION, EXPRESSION, AND IMMUNOGENICITY OF KAPOSIS SARCOMA-ASSOCIATED HERPESVIRUS-ENCODED SMALL VIRAL CAPSID ANTIGEN

We describe a recombinant antigen for use in serologic tests for antib odies to Kaposi's sarcoma (KS)associated herpesvirus (KSHV). The cDNA for a small viral capsid antigen (sVCA) was identified by immunoscreen ing of a library prepared from the BC-1 body cavity lymphoma cell line induced into KSHV lytic gene expression by sodium butyrate, The cDNA specified a 170-amino-acid peptide with homology to small viral capsid proteins encoded by the BFRF3 gene of Epstein-Barr virus and the ORF6 5 gene of herpesvirus saimiri, KSHV sVCA was expressed from a 0.85-kb mRNA present late in lytic KSHV replication in BC-1 cells, This transc ript was sensitive to phosphonoacetic acid and phosphonoformic acid, i nhibitors of herpesvirus DNA replication. KSHV sVCA expressed in mamma lian cells or Escherichia coli or translated in vitro was recognized a s an antigen by antisera fi om KS patients. Rabbit antisera raised to KSHV sVCA expressed in E. coli detected a 22-kDa protein in KSHV-infec ted human B cells. Overexpressed KSHV sVCA purified from E. coli and u sed as an antigen in immunoblot screening assay did not cross-react wi th EBV BFRF3. Antibodies to sVCA were present in 89% of 47 human immun odeficiency virus (HIV)-positive patients with KS, in 20% of 54 HIV-po sitive patients without KS, but in none of 122 other patients includin g children born to HIV-seropositive mothers and patients with hemophil ia, autoimmune disease, or nasopharyngeal carcinoma, Low-titer antibod y was detected in three sera from 28 healthy subjects. Antibodies to r ecombinant sVCA correlate with KS in high-risk populations. Recombinan t sVCA can he used to examine the seroepidemiology of infection with K SHV in the general population.