Study of T4SS-secreted proteins from Brucella as potencial vaccine candidates.

M. VICTORIA DELPINO; JULIANA CASSATARO; SILVIA ESTEIN; CARLOS A. FOSSATI; PABLO C. BALDI

Córdoba, Córdoba, Argentina

Congreso; VII Latin American Congress of Immunology (ALAI); 2005

Abstract The type IV secretion system (T4SS, virB genes) from Brucella spp is believed to secrete virulence factors. We identified 3 proteins apparently secreted through the T4SS: coloil glycine hydrolase (CGH), peptidyl prolyl cis trans isomerase (SurA) and DnaK. To test the protective role of immune responses to these factors, mice were immunized (3 doses) intraperitoneally (ip) with CGH, SurA or DNAk (recombinant proteins) in Freund adjuvant (IFA). CGH deconjugates biliary salts and is a virulence factor in orally-acquired pathogens. Therefore, protection by oral immunization with CGH and cholera toxin, or cholera toxin alone (4 weekly doses) was also tested. Positive vaccination controls received heat-killed B. melitensis in IFA, and negative controls PBS. Challenges with live B. melitensis (oral or i.p.) were done 30 days later. Protection was calculated as the difference between mean log CFU (spleen) in vaccinated groups versus the PBS group. As measured by ELISA, specific serum IgG2a titers after the last i.p. CGH dose were higher than IgG1 ones (40.000 vs. 25.000), but the inverse was true for SurA (30.000 vs. 45.000). These immunizations protected against i.p. Brucella infection (CGH = 1,11 log, SurA= 1,45 log). CGH-specific IgA levels increased after oral immunization (two-fold in feces, three-fold in serum). Protection data for i.p. DnaK and oral CGH will be available in due course. These results suggest that T4SS-secreted factors may be useful for vaccination against Brucella.