The antigenicity of the chicken anaemia virus protein VP3 (Apoptin)

Chicken anaemia virus protein VP3 (Apoptin) was cloned and expressed as a recombinant protein and evaluated for its suitability as a serodiagnostic reagent. VP3 was expressed as a fusion protein either with glutathione S -transferase or with a six-histidine tag. Both recombinant proteins reacted specifically with anti-VP3 monoclonal antibodies and with serum from vaccinated chickens by Western blot and by enzyme-linked immunosorbent assay (ELISA). However, when testing sera from birds of different ages and genetic backgrounds, high non-specific reactions were evident and false positives were observed, especially in older birds. This suggests that VP3 is poorly immunogenic during infection and low antibody concentrations are masked by non-specific reactions. Thus, VP3 is not suitable for use as antigen in ELISAs.