%0 Journal Article %A Olsen, Christopher W. %A Corapi, Wayne V. %A Jacobson, Richard H. %A Simkins, Ronald A. %A Saif, Linda J. %A Scott, Fred W. %T Identification of antigenic sites mediating antibody-dependent enhancement of feline infectious peritonitis virus infectivity %D 1993 %J Journal of General Virology, %V 74 %N 4 %P 745-749 %@ 1465-2099 %R https://doi.org/10.1099/0022-1317-74-4-745 %I Microbiology Society, %X We have previously demonstrated antibody-dependent enhancement of feline infectious peritonitis virus (FIPV) infection of macrophages using both virus-specific antisera and monoclonal antibodies (MAbs) to the spike (S) protein of FIPV. To increase our understanding of this phenomenon, six representative MAbs from a previously documented group of 12 enhancing MAbs were used to identify epitopes that mediate antibody-dependent enhancement of FIPV infectivity. Analysis of the results of kinetics-based competitive ELISA (K-cELISA) among these six enhancing MAbs grouped the epitopes into two clusters. Because transmissible gastroenteritis virus (TGEV) and FIPV are so closely related antigenically, we also conducted K-cELISA experiments between the FIPV MAbs and TGEV S protein-specific MAbs for which the epitopes had previously been mapped to specific sites on the TGEV S protein. Results of these assays indicated that the two FIPV epitope clusters are homologues of the previously defined TGEV S protein sites A and E/F. In addition, two TGEV S protein-specific MAbs also induced antibody-dependent enhancement of FIPV infection of macrophages. This functional cross-reactivity provides further support for the close antigenic relationship between FIPV and TGEV. Our results provide a preliminary localization of several enhancing epitopes within the amino acid sequence of the FIPV S protein. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-74-4-745