Immunization with Brucella VirB proteins elicits a protective Th1 immune response in mice and a similar immune response in dogs.

POLLAK, C.N.; WANKE, M.M.; ESTEIN, S.M.; DELPINO, M.V.; MONACHESI, N.E.; COMERCIO, E.A.; FOSSATI, C.A.; BALDI, P.C.

CLINICAL AND VACCINE IMMUNOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2015

1556-6811

VirB proteins from Brucella spp. constitute the type IV secretion system, a key virulence factor mediating the intracellular survival of these bacteria. Here, we assessed whether a Th1-type immune response against VirB proteins may protect mice from Brucella infection and whether this response can be induced in the dog, a natural host for Brucella. Splenocytes from mice immunizedwith VirB7 or VirB9 responded to their respective antigens with significant and specific production of gamma interferon (IFN-), whereas interleukin-4 (IL-4) was not detected. Thirty days after an intraperitoneal challenge with live Brucella abortus, the spleen load of bacteria was almost 1 log lower in mice immunized with VirB proteins than in unvaccinated animals. As colonization reduction seemed to correlate with a Th1-type immune response against VirB proteins, we decided to assesswhether such a response could be elicited in the dog. Peripheral blood mononuclear cells  (PBMCs) from dogs immunized with VirB proteins (three subcutaneous doses in QuilA adjuvant) produced significantly higher levels of IFN- than cells from control animals upon in vitro stimulation with VirB proteins. A skin test to assess specific delayed-type hypersensitivity was positivein 4 out of 5 dogs immunized with either VirB7 or VirB9. As both proteins are predicted to locate in the outer membrane of Brucella organisms, the ability of anti-VirB antibodies to mediate complement-dependent bacteriolysis of B. canis was assessed in vitro. Sera from dogs immunized with either VirB7 or VirB9, but not from those receiving phosphate-buffered saline (PBS), produced significant bacteriolysis. These results suggest that VirB-specific responses that reduce organ colonization by Brucella in mice can be also elicited in dogs.