Epitope mapping and the detection of transmissible gastroenteritis viral proteins in cell culture using biotinylated monoclonal antibodies in a fixed-cell ELISA

A fixed-cell ELISA was developed using swine testicle (ST) cells infected with the virulent Miller strain of transmissible gastroenteritis virus (TGEV) and purified biotinylated monoclonal antibodies (b-MAbs). Five of the b-MAbs were specific for the peplomer (E2), five reacted to the nucleocapsid (N), and one reacted to the E1 protein of the Miller strain of TGEV. Protein A-Sepharose purification of MAbs yielded protein concentrations ranging from 0.40 to 3 mg per ml of ascites. Separate pools of N-MAbs and E2-MAbs, and the E1-MAb were used to monitor synthesis of TGE viral antigen in ST cells from 0 to 16 h post-infection at various multiplicities of infection (MOI). Epitopes of N proteins appeared sooner and at a lower MOI than those for the E1 and E2 proteins. The fixed-cell ELISA was also used to examine relative binding affinities of TGEV MAbs. Concentrations of b-MAbs producing a half-maximal signal ranged from 0.11 to 3.8 µg/ml for E2-MAbs, from 0.05 to 0.82 µg/ml for N-MAbs, and 6 µg/ml for the E1-MAb. The assay was used to determine the 50% neutralization concentrations for four neutralizing E2-MAbs (0.1 µg/ml to 6.9 µg/ml) and one E1-MAb (1.2 µg/ml). Competition assays between b-MAbs and unlabeled competitors indicated that at least two major antigenic sites exist on the E2-protein and 2 to 3 antigenic sites are present on the N-protein of Miller TGEV.