EPITOPES ON THE SPIKE PROTEIN OF A NEPHROPATHOGENIC STRAIN OF INFECTIOUS-BRONCHITIS VIRUS

Infectious bronchitis virus (IBV), the first coronavirus described, wa s initially associated with severe respiratory disease. However, outbr eaks have more recently also been associated with nephropathogenesis. Topographically interrelated antigenic determinants of the nephropatho genic Gray strain of IBV were characterized using eleven monoclonal an tibodies (MAbs). Four MAbs (IgG 2akappa) defined epitopes that were bo th conformation-independent and group specific, reacting with Gray, Ar kansas (Ark), and Massachusetts 41 (Mass 41) strains. Seven MAbs (IgG 1kappa) defined conformation-dependent epitopes that could differentia te the Gray from the Ark and Mass strains. The spike protein specifici ty of the MAbs was determined with the conformation-independent MAbs a nd one MAb that reacted only in ''non-denaturing'' western blot assays . Competitive binding studies using these MAbs suggested a high degree of functional dependency among the associated epitopes as might be ex pected with a protein of complex secondary and tertiary structure. At least two regions associated with complete protection of infected embr yos were identified that consisted of both conformation-dependent and independent epitopes. However, a ''non-neutralizing'' MAb, which did n ot protect the embryo from gross lesions, did inhibit virus-induced le sions and replication in the kidneys. These MAbs should be valuable to ols in studying IBV pathogenesis.