Synthetic peptides deduced from the amino acid sequence of Epstein‐Barr virus nuclear antigen 6 (EBNA 6): Antigenic properties, production of monoreactive reagents, and analysis of antibody responses in man

Studies on the antibody responses to various Epstein-Barr virus (EBV) antigens have been instrumental in the understanding of the seroepidemiology and diagnosis of this viral infection and the subsequent carrier state. While antibodies to the viral capsid antigen (VCA), early antigen (EA), and nuclear antigens 1 and 2 (EBNA 1 and 2) have been well characterized, the antibody response to the other nuclear antigens is not well understood. EBNA 6 is expressed by lymphoblasts during acute EBV infection and may be an important antigen for diagnosis and evaluation of the immune response. In order to analyze the antibody response to EBNA 6, ten peptides (20–21 amino acids), deduced from the EBNA 6 coding region, were synthesized and evaluated for antigenicity by ELISA. One peptide (p-63; PA-PQAPYQGYQEPPAPQAPY) derived from the amino acid repeats showed the highest specific reactivity with human sera. This peptide was evaluated further for detection of human EBNA 6-reactive antibodies. Forty-two of forty-nine (86%) EBV-seropositive healthy donors had p-63- specific IgG reactivity, while none of 50 EBV seronegative patients reacted with the p-63 peptide. Twenty-two of fifty-one (43%) patients with ongoing primary EBV infection had detectable p-63-specific IgG. Serum samples drawn sequentially from patients during and after primary EBV infection revealed an increase in p-63-reactive IgG over time. A similar pattern was found for reactivity with an EBNA I-specific peptide (p-107), in contrast to the EBNA 2 (polyproline) response, which decreased over time. Some EBV seropositive individuals who had no detectable IgG against peptide p-63 did have antibodies against the native EBNA 6 by anticomplement immunofluorescence to EBNA 6 transfected cells. Rabbit antiserum raised against p-63 reacted specifically with native EBNA 6 by an immunofluorescence assay and by immunoblotting, indicating the EBNA 6-specific antigenicity of the peptide. Thus, the peptide p-63 derived from the amino acid repeats of the EBNA 6 coding region constitutes a predominant, although not exclusive, epitope in the EBNA 6 antibody response. © 1995 Wiley-Liss, Inc.