Comparison of the Antibody Response in Adult Cattle Against Different Epitopes of Brucella abortus Lipopolysaccharide

Abstract

The comparison of serological responses in a sample of adult, vaccinated and ®eld-infected bovines with Brucella abortus is reported. Indirect enzyme immunoassay (EIA) titration curves and Western blotting tests for smooth-type lipopolysaccharide (S-LPS), rough-type LPS (R-LPS) and lipid A were performed. In the initial screening of sera, an overall prevalence of 20.5 % was found, which corresponds to a country with a high incidence of brucellosis. End-point EIA titres against LPS antigens from vaccinated and ®eld-infected cows were not signi®cantly different. However, the absorbance values in the titration curves were signi®cantly higher for S-LPS as compared with the other antigens. A high correlation coef®cient (r 0.933) was obtained when the titres to R-LPS versus lipid A were compared. Western blotting reactions of vaccinated and ®eld-infected animals were indistinguishable. S-LPS, R-LPS and lipid A epitopes were recognized in a heterogeneous manner. In general, the number of bovines that reacted against LPS was higher in the ®eld-infected group, with a stronger binding to S-LPS. Based on our observations, the vaccinated and ®eldinfected bovines are capable of producing similar antibody responses to the Brucella main outer surface antigen, LPS. It should be emphasized that the humoral response of cattle to Brucella LPS contains signi®cant amounts of antibodies to other antigenic moieties of this important surface molecule, which may contribute to the immunity to brucellosis.

Improvement in the diagnosis of Brucella abortus infections in naturally infected water buffaloes (Bubalus bubalis) using an ELISA with a Protein-G-based indicator system

“…However, such reactions could be due to antibodies directed against antigenic determinants located deep into Brucella LPS complex which are not readily exposed in RBT, but accessible in purified LPS when used for coating the plates. This phenomenon has been shown to occur in bovines and other animals that are capable of generating antibodies against deep determinants of LPS such as core and lipid A moieties (Rojas et al 2001). Secondly, low avidity agglutinins or reduced amounts of antibodies in some carrier animals would result in negative RBT reaction.…”