Vaccination with Brucella abortus Recombinant In Vivo-Induced Antigens Reduces Bacterial Load and Promotes Clearance in a Mouse Model for Infection

Abstract

Current vaccines used for the prevention of brucellosis are ineffective in inducing protective immunity in animals that are chronically infected with Brucella abortus, such as elk. Using a gene discovery approach, in vivo-induced antigen technology (IVIAT) on B. abortus, we previously identified ten loci that encode products up-regulated during infection in elk and consequently may play a role in virulence. In our present study, five of the loci (D15, 0187, VirJ, Mdh, AfuA) were selected for further characterization and compared with three additional antigens with virulence potential (Hia, PrpA, MltA). All eight genes were PCR-amplified from B. abortus and cloned into E. coli. The recombinant products were then expressed, purified, adjuvanted, and delivered subcutaneously to BALB/c mice. After primary immunization and two boosts, mice were challenged i.p. with 5×104 CFU of B. abortus strain 19. Spleens from challenged animals were harvested and bacterial loads determined by colony count at various time points. While vaccination with four of the eight individual proteins appeared to have some effect on clearance kinetics, mice vaccinated with recombinant Mdh displayed the most significant reduction in bacterial colonization. Furthermore, mice immunized with Mdh maintained higher levels of IFN-γ in spleens compared to other treatment groups. Collectively, our in vivo data gathered from the S19 murine colonization model suggest that vaccination with at least three of the IVIAT antigens conferred an enhanced ability of the host to respond to infection, reinforcing the utility of this methodology for the identification of potential vaccine candidates against brucellosis. Mechanisms for immunity to one protein, Mdh, require further in vitro exploration and evaluation against wild-type B. abortus challenge in mice, as well as other hosts. Additional studies are being undertaken to clarify the role of Mdh and other IVI antigens in B. abortus virulence and induction of protective immunity.

Vaccination against a Virus-Encoded Cytokine Significantly Restricts Viral Challenge

“…This, however, is the singular example in which vaccination against the microbial activator of IL-10R signaling induces protective efficacy (i.e., vaccine-induced reductions in infection and/or disease). In contrast, vaccination of mice with either the YopM type III secretion system protein of Yersinia pestis or the PrpA virulence factor of Brucella abortus does not induce any protective efficacy against bacterial challenge (46,47). Since, in the case of YopM, purified protein can enter into the cell by "autonomous translocation" (48), vaccination with an unmodified form of the protein may preclude the efficient induction of antibodies that neutralize the function of the protein during primary challenge.…”

RNA-seq reveals the critical role of CspA in regulating Brucella melitensis metabolism and virulence

“…The ability of brucellae to survive within macrophages is essential for their virulence (Celli and Gorvel, 2004). In the past few years, hundreds of virulence-related genes have been identified by transposon mutagenesis (Wu et al, 2006), in vivo-induced antigen technology (Lowry et al, 2011), DNA microarray hybridization (Tian et al, 2013), and bioinformatics (He, 2012), which include lipopolysaccharide (Seleem et al, 2008), the type IV secretion system T4SS (Seleem et al, 2008;Martirosyan et al, 2011), the quorum-sensing-related transcriptional regulator VjbR , the BvrR/BvrS two-component regulatory system (Sola-Landa et al, 1998;Martinez-Nunez et al, 2010), and the periplasmic cyclic -1,2 glucans (Briones et al, 2001), among others. Interestingly, most of these genes are not direct virulence factors, but are transcription regulators, such as VjbR which can control the expression of virulence factors to affect Brucella virulence .…”

Pathogen Manipulation of cIL-10 Signaling Pathways: Opportunities for Vaccine Development?

“…In support of this idea, it has been reported that purified YopM can undergo "autonomous translocation" into the interior of mammalian cells (Ruter et al 2010). Vaccination/challenge results comparable to those observed for YopM were noted for immunization with the PrpA virulence factor of B. abortus (Lowry et al 2011), a protein that acts as a B cell mitogen and stimulates expression of cIL-10 ( Spera et al 2006). Despite eliciting high binding antibody titers, mice immunized with wild-type PrpA were not protected from B. abortus challenge.…”