HUMORAL IMMUNE-RESPONSE AGAINST LIPOPOLYSACCHARIDE AND CYTOPLASMIC PROTEINS OF BRUCELLA-ABORTUS IN CATTLE VACCINATED WITH B-ABORTUS S19 OR EXPERIMENTALLY INFECTED WITH YERSINIA-ENTEROCOLITICA SEROTYPE-0-9

The humoral immune responses against three different antigens of Bruce lla abortus were monitored by enzyme-linked immunosorbent assay in cat tle vaccinated with B. abortus S19 or experimentally infected with Yer sinia enterocolitica serotype 0:9. Immunoglobulin G (IgG) and IgM resp onses against (i) B. abortus lipopolysaccharide (LPS), (ii) total cyto plasmic proteins depleted of LPS (LPS free CYT), and (iii) B. abortus 18-kDa cytoplasmic protein were measured. Vaccinated animals and Yersi nia-infected animals developed high anti-LPS IgM and IgG titers, which overlapped with those obtained with sera from B. abortus 544-infected animals used as positive controls. In contrast, only a slight or nega tive IgG and IgM response against LPS-free CYT and the 18-kDa protein was detected in vaccinated or Yersinia-infected cattle, although its l evels were always significantly lower than those of B. abortus 544 inf ected animals. These data indicate that cytoplasmic proteins of B. abo rtus could be useful for the differential diagnosis of bovine brucello sis.