Serodiagnosis of Epstein-Barr virus infection by using recombinant viral capsid antigen fragments and autologous gene fusion

Using recombinant 15- to 30-kDa fragments and fusion with glutathione S-tra nsferase (GST), we investigated the seroreactivity of three large structura l proteins of Epstein-Barr virus (EBV), p150 (BcLF1, capsid), p143 (BNRF1, tegument), and gp125 (BALF4, membrane) in Western blots. None of 13 fragmen ts tested, however, was qualified for diagnostic application. In contrast, the two small viral capsid antigens (VCA), p18 (BFRF3) and p23 (BLRF2), dem onstrated sensitive (100%) EBV-specific immunoglobulin G (IgG) reactivities , While p18 additionally showed maximum sensitivity for IgM detection, the IgM sensitivity of p23 was restricted (44%), An autologous fusion protein, p23-p18, which consists N-terminally of full-length p23, followed by the ca rboxy half of p18, was constructed. This antigen was subjected to indirect VCA enzyme-linked immunosorbent assays (ELISAs), for IgG and IgM, as well a s to a mu-capture (mu c) IgM ELISA. All assays were found to be 100% specif ic when EBV-negative sera were tested. Using sera from previously infected individuals, the p23-p18 fusion revealed an improved IgG sensitivity of 99% compared to sensitivities of 97 and 93% for the single antigens p18 and p2 3, respectively. The sensitivity and specificity of the indirect IgM ELISA with samples of primary and past infections, respectively, were 100%, The p c principle for IgM overcame completely the interference by rheumatoid fact ors. Compared to the specificity of the indirect IgM version, the specifici ty with sera collected from rheumatoid arthritis patients increased from 48 to 100%, In summary, the p23-p18 IgG and mu c IgM ELISAs showed excellent performances and are promising new diagnostic tests for the detection of EB V-specific antiviral capsid antibodies.