Antigenic analysis of feline coronaviruses with monoclonal antibodies (MAbs): preparation of MAbs which discriminate between FIPV strain 79-1146 and FECV strain 79-1683.

We prepared 31 monoclonal antibodies (MAbs) against either FIPV strain 79-1146 or FECV strain 79-1683, and tested them for reactivity with various coronaviruses by indirect fluorescent antibody assay (IFA). Sixteen MAbs which reacted with all of the 11 strains of feline coronaviruses, also reacted with canine coronavirus (CCV) and transmissible gastroenteritis virus (TGEV). In many of them, the polypeptide specificity was the recognition of transmembrane (E1) protein of the virus. We succeeded in obtaining MAbs which did not react with eight strains of FIPV Type I viruses (showing cell-associated growth) but reacted with FIPV Type II (79-1146, KU-1) and/or FECV Type II (79-1683) (showing non-cell associated growth). These MAbs also reacted with CCV or TGEV. These MAbs recognized peplomer (E2) glycoprotein, and many antigenic differences were found in this E2 protein. These results suggest that FIPV Type II and FECV Type II viruses are antigenically closer to TGEV or CCV than to FIPV Type I viruses. Furthermore, the MAb prepared in this study has enabled discrimination between FIPV strain 79-1146 and FECV strain 79-1683, which was thought to be impossible by the previous serological method.