Cross-reactivity of Epstein-Barr virus-specific immunoglobulin M antibodies with cytomegalovirus antigens containing glycine homopolymers

Timely and reliable detection of acute primary human cytomegalovirus (HCMV) infection is important in prenatal screening programs and for differential diagnosis of infectious mononucleosis-like disease. Enzyme-linked immunoso rbent assays (ELISAs) based on HCMV proteins enable the sensitive detection of immunoglobulin M (IgM) antibodies during primary infection. However, co ncerns have been raised about possible cross-reactivities of the HCMV antig ens used for the design of such ELISAs with IgM antibodies induced by Epste in-Barr Virus (EBV). In this study we investigated whether IgM antibodies g enerated during acute EBV infection reacted with recombinant HCMV antigens. Serum samples from patients with primary EBV infection frequently scored p ositive when tested in different HCMV IgM ELISAs, irrespective of whether c onventional or recombinant antigens were used for the design of the HCMV Ig M assays. Such cross-reactive IgM antibodies were found to be directed agai nst short glycine-rich motifs contained within the nonstructural HCMV prote ins pUL44 and pUL57. Further analyses revealed that these glycine-rich moti fs were major antigenic domains for IgM antibodies induced during HCMV infe ction. Their deletion from recombinant proteins abrogated reactivity with I gM synthesized during HCMV infection. EBV-induced IgM antibodies that react ed with HCMV antigens showed similar kinetics of reactivity in HCMV- or EBV -specific assays in the course of primary EBV infection, indicating that th e two populations of antibodies were highly overlapping. The results demons trate that primary EBV infection leads to the induction of IgM antibodies t hat specifically bind to widely used diagnostic antigens of HCMV. This has to be considered in the interpretation of HCMV-specific IgM assays.