Specific antibodies reactive with the 22-kilodalton major outer surface protein of Borrelia anserina Ni-NL protect chicks from infection

An outer surface lipoprotein of 22 kDa was identified in the avian pathogen Borrelia anserina NI-NL by using antibody preparations reactive with bacte rial surface-exposed proteins. Amino acid sequence analysis of the 22-kDa p rotein demonstrated 90% identity with VmpA of B. turicatae, suggesting that the protein belongs to the family of 20-kDa outer surface proteins of the genus Borrelia, All of the 60 chicks intramuscularly treated with antibodie s specifically reacting with the 22-kDa protein and infected with strain Ni -NL were completely protected from infection, since no spirochetemia was de tected, and from death. Control chicks were treated with immune sera raised against apathogenic strain B. anserina Es, which expresses a prominent 20- kDa polypeptide that is also a member of the Vmp family but does not cross- react immunologically with the 22-kDa protein of the Ni-NL strain. These an imals, infected with B, anserina NI-NL, showed a high degree of spirochetem ia 10 days after infection, and all died between 14 and 21 days after infec tion. The results showed that the 22-kDa surface protein of B, anserina NI- NL is a determinant of the pathogenic potential of the strain and also conf irmed that only strain-specific antibodies are protective against B. anseri na infection.