The reactivity of monoclonal antibodies against orf virus with other parapoxviruses and the identification of a 39 kDa immunodominant protein

A panel of 27 mouse monoclonal antibodies (Mabs) was raised against orf vir us. Sixteen of these Mabs reacted with a protein with a molecular mass of 6 5 kDa, 8 reacted with a protein with a molecular mass of 39 kDa and three r emain uncharacterised. Reactivity of the Mabs with a library of recombinant vaccinia viruses expressing various regions of the NZ-2 orf virus genome i dentified the approximate positions of the genes encoding these 2 immunodom inant orf virus proteins. The gene encoding the 39 kDa protein was identifi ed and sequenced. The protein was detected in an envelope fraction of orf v irus and was shown to be homologous to the envelope protein encoded by the H3L gene of vaccinia virus. The 65 kDa protein has not been fully character ised, but the gene encoding it has been localised to a 10 kbp region of the orf virus genome. The Mabs were used to discriminate 4 parapoxviruses deri ved from sheep, 2 from cattle and 1 each fi-om a seal and squirrel. Eightee n Mabs reacted with all 4 sheep viruses, 19 Mabs reacted with both cattle v iruses, 6 recognised seal parapoxvirus and 2 recognised the squirrel parapo xvirus. Only one of the 27 Mabs reacted with all 8 parapoxviruses suggestin g it recognises a conserved epitope within the genus.