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

DELPINO MV,; CASSATARO J,; ESTEIN SM,; FOSSATI CA,; PABLO CESAR BALDI

Córdoba

Congreso; VII Congreso Latinoamericano de Inmunología; 2005

Brucella spp expresses a type IV secretion system (T4SS, virB genes), which is believed to secrete virulence factors. We have 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 the immune response to these factors, mice were immunized intraperitoneally (ip) with CGH, SurA or DNAk (recombinant proteins) in Freund adjuvant (3 doses). CGH deconjugates biliary salts, acting as a virulence factor in pathogens infecting through the oral route. To test whether mucosal anti-CGH antibodies protect against Brucella, mice were orally immunizated with CGH (100 ug) and cholera toxin (10 ug), or cholera toxin alone (4 weekly doses). Positive controls were immunized with heat-killed B. melitensis in IFA, and negative controls with PBS. Thirty days after the last immunization, mice were challenged orally or i.p. with live Brucella melitensis H38. Protection was calculated as the difference between mean log CFU (spleen) in vaccinated groups versus the PBS group. Serum or fecal levels of specific antibodies were measured by indirect ELISA. Serum IgG2a titers after the last immunization were higher than IgG1 ones (40.000 vs. 25.000) in the CGH group, but the inverse was true for the SurA group (30.000 vs. 45.000). In the orally immunized group, CGH-specific IgA antibodies increased after immunization (two-fold in feces, three-fold in serum). These specific immune responses protected against Brucella infection through the i.p. route (CGH = 1,11 log, SurA= 1,45 log). Protection data for DnaK and oral CGH immunizations will be available in due course.