Deletion of the Braun Lipoprotein-Encoding Gene and Altering the Function of Lipopolysaccharide Attenuate the Plague Bacterium

Braun (murein) lipoprotein (Lpp) and lipopolysaccharide (LPS) are major components of the outer membranes of Enterobacte-riaceae family members that are capable of triggering inflammatory immune responses by activating Toll-like receptors 2 and 4, respectively. Expanding on earlier studies that demonstrated a role played by Lpp in Yersinia pestis virulence in mouse models of bubonic and pneumonic plague, we characterized anmsbB in-frame deletion mutant incapable of producing an acyltransferase that is responsible for the addition of lauric acid to the lipid Amoiety of LPS, as well as alppmsbB double mutant of the highly virulent Y. pestis CO92 strain. Although themsbB single mutant was minimally attenuated, thelpp single mutant and thelppmsbB double mutant were significantly more attenuated than the isogenic wild-type (WT) bacterium in bubonic and pneumonic animal models (mouse and rat) of plague. These data correlated with greatly reduced survivability of the aforemen-tionedmutants in murine macrophages. Furthermore, thelppmsbB double mutant was grossly compromised in its ability to disseminate to distal organs in mice and in evoking cytokines/chemokines in infected animal tissues. Importantly, mice that sur-vived challenge with thelppmsbB double mutant, but not thelpp ormsbB single mutant, in a pneumonic plague model were significantly protected against a subsequent lethal WT CO92 rechallenge. These data were substantiated by the fact that the lppmsbB double mutant maintained an immunogenicity comparable to that of theWT strain and induced long-lasting T-cell responses against heat-killedWT CO92 antigens. Taken together, the data indicate that deletion of themsbB gene augmented th