Localization of brucella antigens that elicit a humoral immune response in Brucella abortus-infected cells

Localization of brucella antigens, to which brucella-infected cattle make antibodies, and the surface characteristics of Brucella abortus smooth strain 19 and rough strain 45/20 were studied by the use of monospecific antisera in absorption tests, electron microscopy, and electrophoretic mobility of organisms in microelectrophoresis. Antigenic determinants of electrophoretically defined antigen A5 were present on the surface of B. abortus rough strain 45/20 organisms, and protein moieties were most probably exposed on the surface of this strain in contrast with smooth strain 19 organisms. Several antigens distinct from the smooth lipopolysaccharide complex, to which brucella-infected cattle make antibodies, were not detected on the surface of smooth organisms. Agglutinating antibodies present in anti-B. abortus strain 19 serum did not bind to all areas on the surface of the smooth cells, suggesting the presence of different antigenic moieties on their surface. It is also postulated that the surface of B. abortus rough strain 45/20 displays receptors able to strongly bind immunoglobulin molecules, as well as other serum components.