Antigenic comparison of feline coronavirus isolates: evidence for markedly different peplomer glycoproteins.

The antigenic relationships among seven feline coronavirus isolates were investigated by using a panel of 26 monoclonal antibodies (MAbs). The MAbs were categorized into five immunoreactive groups which were used to delineate two antigenic types of feline coronaviruses. One antigenic type included the more virulent feline infectious peritonitis virus (FIPV) isolates (FIPV-UCD-1, FIPV-UCD-4, FIPV-TN406, FIPV-DF2, and FIPV-79-1146), whereas the second antigenic type was composed of the avirulent isolate FIPV-UCD-2. The feline enteric coronavirus isolate FECV-79-1683 shared some characteristics of both of the major antigenic groups. Epitopes on the nucleocapsid and envelope polypeptides were in general highly conserved among both antigenic types, although a few type-specific antigenic sites were discriminated. The most striking finding was the marked antigenic difference in the peplomer (E2) glycoproteins between the two antigenic types. Seven anti-E2 MAbs reacted with one antigenic type of E2, whereas seven other anti-E2 MAbs recognized a different antigenic form of E2. None of the 14 anti-E2 MAbs reacted with all of the isolates.