Identification and characterization of the major proteins of malignant catarrhal fever virus

Malignant catarrhal fever virus (MCFV), a gamma-herpesvirus, causes a severe inflammatory and lymphoproliferative disease of cattle and other susceptible ruminants. Polyclonal antisera and monoclonal antibodies (MAbs) to the Minnesota isolate of MCFV were produced and used to examine the characteristics of the viral proteins. Immunoprecipitation of antigens of the Minnesota isolate of MCFV with polyclonal antisera revealed at least 11 proteins with molecular masses ranging from 17 kDa to 145 kDa. Among 279 candidate anti-MCFV hybridomas, 14 were selected and clustered into six groups on the basis of the patterns of reactivity to viral proteins in immunoprecipitation and immunoblot. The group I MAbs exhibited strong neutralizing activity and recognized a glycosylation-dependent conformational epitope on a 110 kDa protein. The MAbs in group II bound a non-neutralizing conformational epitope on a 130 kDa non-glycosylated protein. A glycosylated protein complex of 115/110/105/78/45 kDa moieties was identified by the MAbs in group III. The MAbs in groups IV, V and VI reacted with non-glycosylated proteins of 36/34 kDa, 24 kDa and 17 kDa, respectively. Comparison of three MCFV isolates [the Minnesota isolate, the Austrian isolate (Au-732) and the African prototype isolate (WC-11)] revealed no apparent differences in immunoprecipitation patterns with the single exception that the 110 kDa protein of WC-11 was slightly smaller than its counterpart in the Minnesota isolate.