Cell-free-antigen (CFA) vaccines of strain Y-1 (serotype 1), G-4 (serotype 2) and E-3 (serotype 5) of Actinobacillus pleuropneumoniae (A. pleuropneumoniae) were prepared by emulsifying concentrated culture supernatant with oil-adjuvant. Mice immunized with the CFA vaccine had a high survival rate (90-100%) against challenge with the homologous strain. They also had cross-protective activity against challenge with the heterogeneous strains but their survival rate was low (20-50%). On the other hand, mice immunized with whole cell vaccine showed serotype specific protection and only a little cross protection. The protective antigens of the CFA were investigated. MAbs were produced by the standard method using spleen cells of mice immunized with CFA. MAbs to Apx I, II, III and capsular antigen of serotype 5 were obtained. Only MAbs to Apx I showed hemolysin neutralization activity among them. The protective effect of these MAbs against A. pleuropneumoniae infection were examined by passive immunization. Administration of Apx I MAb to mice extended survival time after challenge with serotype 5. The mice showed partial cross-protection against challenge with serotype 1. Survival rate was considerably low after the challenge infection. None of the mice given MAbs to Apx II or III were protected against challenge with serotype 5. The mice given MAb to capsular antigen of serotype 5 had a high survivalrate (70%) against a challenge with a homologous serotype. Furthermore, mice given MAbs against Apx I and capsular antigen of serotype 5 were completely protected against a challenge with A. pleuropneufnoniae serotype 5. In this study, we concluded that capsular antigen and Apx I are identified as protective antigens and their antibody play an important role in protection against infection with A. Pleuropneumoniae serotype 5.
Journal of The Japanese Society of Veterinary Science