Multiple roles for Bordetella lipopolysaccharide molecules during respiratory tract infection

Bordetella pertussis, Bordetella parapertussis, and Brodetella bronchisepti ca are closely related subspecies that cause respiratory tract infections i n humans and other mammals and express many similar virulence factors. Thei r lipopolysaccharide (LPS) molecules differ, containing either a complex tr isaccharide (B. pertussis), a trisaccharide plus an O-antigen-like repeat ( B. bronchiseptica), or an altered trisaccharide plus an O-antigen-like repe at (B. parapertussis). Deletion of the wlb locus results in the loss of mem brane-distal polysaccharide domains in the three subspecies of bordetellae, leaving LPS molecules consisting of lipid A and core oligosaccharide. We h ave used wlb deletion (Delta wlb) mutants to investigate the roles of dista l LPS structures in respiratory tract infection by bordetellae. Each mutant was defective compared to its parent strain in colonization of the respira tory tracts of BALB/c mice, but the location in the respiratory tract and t he time point at which defects were observed differed significantly. Althou gh the Delta wlb mutants were much more sensitive to complement-mediated ki lling in vitro, they displayed similar defects in respiratory tract coloniz ation in C5(-/-) mice compared with wild-type (wt) mice, indicating that in creased sensitivity to complement-mediated lysis is not sufficient to expla in the in vivo defects. B. pertussis and B. parapertussis Delta wlb mutants were also defective compared to wt strains in colonization of SCID-beige m ice, indicating that the defects were not limited to interactions with adap tive immunity. Interestingly, the B. bronchiseptica Delta wlb strain was de fective, compared to the wt strain, in colonization of the respiratory trac ts of BALB/c mice beginning 1 week postinoculation but did not differ from the wt strain in its ability to colonize the respiratory tracts of B-cell- and T-cell-deficient mice, suggesting that wlb dependent LPS modifications in B. bronchiseptica modulate interactions with adaptive immunity. These da ta show that biosynthesis of a full-length LPS molecule by these three bord etellae is essential for the expression of full virulence for mice. In addi tion, the data indicate that the different distal structures modifying the LPS molecules on these three closely related subspecies serve different pur poses in respiratory tract infection, highlighting the diversity of functio ns attributable to LPS of gram-negative bacteria.