COMPETITIVE ENZYME-LINKED-IMMUNOSORBENT-ASSAY USING MONOCLONAL-ANTIBODIES TO THE BRUCELLA-MELITENSIS BP26 PROTEIN TO EVALUATE ANTIBODY-RESPONSES IN INFECTED AND BRUCELLA-MELITENSIS REV-1 VACCINATED SHEEP

Competitive enzyme-linked immunosorbent assay (C-ELISA) was performed using 15 monoclonal antibodies (MAbs), specific for Brucella BP26 (pre viously also called CP28), a periplasmic protein antigen, to investiga te antibody responses in naturally and B. melitensis H38 experimentall y infected and B. melitensis Rev.1 vaccinated sheep. The antigen prepa ration consisted of cytosoluble protein extract (CPE) of B. melitensis B115. By combining the C-ELISA results of several MAbs, a high percen tage of naturally infected animals were detected which showed differen t status in the current conventional diagnostic tests. Indeed, 90% of sheep which were positive in the conventional bacteriological and sero logical tests were positive in C-ELISA. 72% of the bacteriologically n egative but serologically and delayed type hypersensitivity positive s heep were also found positive in the C-ELISA. Moreover, 79% of the bac teriologically and serologically negative sheep but delayed type hyper sensitivity positive were also detected by C-ELISA. Thus, these result s confirmed the importance of BP26 as a frequently recognized target o f the humoral immune response of infected sheep. The 8 B. melitensis H 38 experimentally infected sheep showed various degrees of antibody re sponses at the 90th day after infection, which was delayed in comparis on to that against O-polysaccharide (O-PS). Of the 15 MAbs tested, onl y one MAb was weakly inhibited (20 to 35% inhibition) by 56% of negati ve control sera. Furthermore, no antibody response against BP26 was de tected in B. melitensis Rev.1 vaccinated sheep. Results of the C-ELISA with the 15 MAbs showed individual variability of the antibody respon ses against BP26. Thus, it is suggested that several epitopes of BP26 are of interest for diagnosis of B. melitensis infection in sheep.