REACTIVITY OF SERA FROM SHEEP IMMUNIZED WITH INDIVIDUAL OUTER-MEMBRANE PROTEINS OF BACTEROIDES-NODOSUS AGAINST HETEROLOGOUS BACTERIAL STRAINS

To identify those bacterial antigens which might be involved in immunity against ovine foot rot, antisera were raised in sheep to 6 proteins in the outer membrane complex (OMC) of 1 strain of B. nodosus. Examination of the specificity of these antisera by Western blotting, crossed immunoelectrophoresis (XIEP) and IEP, revealed that they recognized the homologous OMC protein, but did not precipitate either undenatratured pilin or OMC, nor could they agglutinate the homologous bacteria. Anti-OMC and anti-pilin sera could precipitate OMC or pili, respectively, and aggluinate whole bacteria. Subsequent analysis of these sera against 5 strains of B. nodosus from different serogroups revealed that proteins 1, 3 and 4 had a similar antigenic structure in all strains examined. The reactivity of anti-pili sera was restricted to homologous bacteria. Anti-pilin sera (raised against denatured pili) also reacted with pilin from 2 of 3 heterologous strains. However, none of the patterns of staining or absorption of any of these sera matched the spectrum of cross-protection afforded by vaccination of sheep with B. nodosus strain 198 cells. THe results question the role of individual OMC proteins in cross-protective immunity and may imply that interactions between several bacterial components are involved in the phenomenon.