Use of complement fixation test to assess humoral immunity in cattle vaccinated with Brucella abortus RB51 rough strain

English. The attenuated Brucella abortus strain RB51 is a lipopolysaccharide (LPS) O-chain-deficient mutant of virulent B. abortus strain 2308. Previous studies showed that B. abortus RB51 vaccine is much less pathogenic and abortigenic, in cattle, than strain B19 or field strains. In addition, unlike B19 strain, the reduced O-chain content in RB51 strain prevents this bacterium from inducing antibodies that can be detectable by conventional serologic tests for bovine brucellosis diagnosis, that predominantly identify antibodies to LPS. Up to now, serologic responses to surface antigens of B. abortus RB51 were measured, in RB51-vaccinated cattle, by an antibody dot-blot assay with acetone-killed B. abortus RB51 as antigen. The purpose of this study was to evaluate the suitability of a Complement Fixation (CF) test performed with B. abortus RB51 strain, previously deprived of anticomplementary activity, in detecting specific anti-B. abortus RB51 antibodies in cattle experimentally vaccinated with this strain. The results, compared with those obtained by CF test and Rose Bengal (RB) test, performed with conventional smooth-type antigens for diagnosis of bovine brucellosis, indicated that this method may provide a very sensitive and specific assay to assess specific humoral immunity to B. abortus RB51 in cattle

Italian. La vaccinazione con il ceppo RB51, mutante in fase rugosa di B. abortus, non e' in grado di indurre, nei bovini, anticorpi rilevabili con le tecniche sierologiche convenzionali che evidenziano soprattutto anticorpi anti-LPS. Per monitorare la risposta anticorpale diretta verso B. abortus RB51 in bovini vaccinati sperimentalmente con tale ceppo, gli AA hanno messo a punto un test di F.d.C.-mi, allestito con l'antigene specifico B. abortus RB51 privato dell'attivita' anticomplementare legata alla natura rugosa del ceppo. I risultati dell'indagine hanno confermato l'assenza di reattivita' dei bovini vaccinati nei confronti degli antigeni brucellari convenzionali in fase S ed evidenziato la capacita' della F.d.C.-mi, allestita con l'antigene RB51, di individuare specificamente e con buona sensibilita' i soggetti trattati con tale ceppo