Serological probes for some foot-and-mouth disease virus nonstructural proteins.

Foot-and-mouth disease virus (FMDV) O1 Kaufbeuren-specific cDNA fragments were subcloned into the E. coli expression vector pRIT.2T. Fusion proteins thus produced in bacteria were purified by affinity chromatography and inoculated into rabbits. Three sera thus obtained were found to be monospecific for FMDV proteins 3A, 3C, and 3D, respectively. Two others were prevalently directed against protein 2C, but in addition, either to protein 2B or to protein 3A. Five out of six mature nonstructural virus proteins can therefore be separately investigated in FMDV-infected cells, either by indirect immunofluorescence or by radioimmunoprecipitation. Immunofluorescence shows all investigated proteins to be located exclusively in the cytoplasm. One of them, protein 2C, transiently forms aggregates at the periphery of cells. Radioimmunoprecipitation confirmed current knowledge on maturation of FMDV proteins. It was further used to characterize postinfectional sera with regard to FMDV-specific antibodies. Cattle and guinea pig were found to have responded differently to FMDV nonstructural antigens. Furthermore, antigenicity of yet to be described FMDV polypeptides was observed in the guinea pig.