Highly specific detection of antibodies to tick-borne encephalitis (TBE) virus in humans using a domain III antigen and a sensitive immune complex (IC) ELISA.

BACKGROUND: In contrast to most antibodies directed to the envelope glycoprotein of flaviviruses, those to the domain III (ED3) show serotype-specific reactions. OBJECTIVES: Only few epitopes are located on the ED3 [Oliphant T, Engle M, Nybakken GE, Doane C, Johnson S, Huang L, et al. Development of a humanized monoclonal antibody with therapeutic potential against West Nile virus. Nat Med 2005;11:522-30; Nybakken GE, Oliphant T, Johnson S, Burke S, Diamond MS, Fremont DH. Structural basis of West Nile virus neutralization by a therapeutic antibody. Nature 2005;437:764-9; Throsby M, Geuijen C, Goudsmit J, Bakker AQ, Korimbocus J, Kramer RA, et al. Isolation and characterization of human monoclonal antibodies from individuals infected with West Nile virus. J Virol 2006;80:6982-92], and highly sensitive assays may be required to detect the small number of human antibodies to this domain. STUDY DESIGN: We have used a sensitive immune complex (IC) ELISA to detect antibodies to the ED3 of TBE virus [Ludolfs D, Niedrig M, Paweska JT, Schmitz H. Reverse ELISA for the detection of anti-West Nile virus IgG antibodies in humans. Eur J Clin Microbiol Infect Dis 2007;26:467-73; Emmerich P, Gunther S, Schmitz H. Strain-specific antibody response to Lassa virus in the local population of west Africa. J Clin Virol 2008;42:40-4]. This assay was compared with two indirect ELISAs using either the ED3 (ED3 ELISA) or whole tissue culture virus (TCV) (TCV ELISA) as source of antigen. Sera of 45 patients with acute TBE infection and of 65 vaccinees were applied to determine the sensitivity of the IC ELISA. RESULTS: The IC ELISA detected antibodies in 107 out of 110 samples of TBE patients and vaccinees, 106 of which were also positive with the TCV ELISA. Both tests had a sensitivity of >or=96%. In contrast, the ED3 ELISA had a sensitivity of only 70%. Using samples of 98 West Africans and of 70 Europeans without any contact to TBE virus or TBE virus antigens, the specificity of the IC ELISA was 100% while the specificity of the commercial TCV ELISA varied between 30% with samples of people with acute dengue fever or with yellow fever vaccination and 100% with samples of students from Hamburg without any previous contact to TBE. CONCLUSION: Obviously, the IC ELISA is able to detect human antibodies to small antigens with only few serotype-specific epitopes with high specificity and sensitivity.