ABSTRACT
Feline infectious peritonitis virus (FIPV) has been isolated several times from infected cats. Some of these isolates vary markedly in their ability to cause disease. Specific-pathogen-free cats were inoculated with the avirulent FIPV-UCD-2 isolate or the extremely virulent FIPV-79-1146 isolate or both. After 1 month, cats which had received FIPV-79-1146 were either dead or showed clinical signs of FIP. All cats which received only FIPV-UCD-2 remained healthy up to 6 months after inoculation. Antibody-mediated immune enhancement of disease was not observed in cats which received FIPV-UCD-2 before inoculation with FIPV-79-1146. Monoclonal antibodies which recognized type-specific epitopes on each of the structural polypeptides of these two viruses were used in competitive-inhibition enzyme-linked immunosorbent assays to analyze the humoral immune responses of the cats. All cats produced antibodies to epitopes found on the homologous virus. In addition, cats inoculated with FIPV-79-1146 also produced antibodies which inhibited the binding of the anti-FIPV-UCD-2 E1 monoclonal antibody. One cat inoculated twice with FIPV-UCD-2 produced antibodies which inhibited the binding of the anti-FIPV-79-1146 N- and E1-specific monoclonal antibodies. Competitive enzyme-linked immunosorbent assays may prove useful in distinguishing cats which are infected with virulent FIPV isolates from cats infected with avirulent feline coronaviruses.
Subject(s)
Antibodies, Viral/biosynthesis , Cat Diseases/immunology , Coronaviridae Infections/veterinary , Coronaviridae/immunology , Peritonitis/veterinary , Animals , Antibodies, Monoclonal/immunology , Antibody Specificity , Antigens, Viral/immunology , Cat Diseases/etiology , Cats , Coronaviridae/pathogenicity , Coronaviridae Infections/etiology , Coronaviridae Infections/immunology , Enzyme-Linked Immunosorbent Assay , Epitopes/immunology , Immunoglobulin G/biosynthesis , Peritonitis/etiology , Peritonitis/immunology , Specific Pathogen-Free Organisms , VirulenceABSTRACT
Isolates of feline infectious peritonitis virus (FIPV) vary in their degree of virulence and have antigenically and functionally different peplomer glycoproteins. We tested the most virulent isolate, FIPV-79-1146 and the avirulent isolate, FIPV-UCD-2 in vivo in order to better understand the pathogenesis of FIP. Specific pathogen free cats were inoculated with either FIPV-79-1146 or FIPV-UCD-2. After 28 days cats which had received FIPV-79-1146 were either dead or showing clinical signs of FIP. The FIPV-UCD-2 inoculated cats seroconverted but remained healthy and were then divided into three groups. One group was not manipulated, one group received a second dose of FIPV-UCD-2, and the third group received FIPV-79-1146. One month later all FIPV-UCD-2 cats which had subsequently received FIPV-79-1146 were dead of FIP while the FIPV-UCD-2 inoculated cats remained healthy. Antibody mediated immune enhancement of FIP disease was not observed. Serum neutralization assays demonstrated that only those cats which received FIPV-79-1146 developed neutralizing antibodies to FIPV-79-1146. However, all cats except uninoculated controls developed neutralizing titers to FIPV-UCD-2. Competition ELISAs were used to analyze the specific humoral immune responses of cats to structural polypeptides of the viruses.