Enhancement and neutralization of feline infectious peritonitis virus infection in feline macrophages by neutralizing monoclonal antibodies recognizing different epitopes.

The interaction between the enhancing and neutralizing activities of three monoclonal antibodies (MAbs) (5-6-2, 6-4-2 and 7-4-1) to the spike protein of feline infectious peritonitis virus (FIPV) strain 79-1146 was determined using feline macrophages. At a high MAb concentration, all of the three MAbs completely inhibited the FIPV infection at 37 C. However, two of them (6-4-2 and 7-4-1) enhanced FIPV infection when either the MAb concentration or reaction temperature was lowered. These MAbs also exerted an immediate infectivity-enhancing activity for up to 10 min of reaction and by 20 min, neutralizing activities were observed. Only MAb 5-6-2 consistently showed neutralizing activity regardless of the reaction conditions. Competition with sera from cats experimentally infected with FIPV strain 79-1146 or feline enteric coronavirus strain 79-1683 showed that the two epitopes recognized by MAb 5-6-2 and MAb 6-4-2, respectively, are also recognized by the natural host.

antibody‐dependent enahancement

Crandell feline kidney

enzyme‐linked immunosorbent assay

feline whole fetus cells

feline enteric coronavirus

feline infectious peritonitis virus

Hanks' balanced salt solution

indirect fluorescent antibody assay

monoclonal antibody

monoclonal antibodies

transmembrane protein

neutralization test

phosphate‐buffered saline solution

respiratory syncytial virus

peplomer spike protein

50% tissue culture infectious dose.