Antigenic Variation among Bordetella

Abstract

The O chain polysaccharide (O PS) of Bordetella bronchiseptica and Bordetella parapertussis lipopolysaccharide is a homopolymer of 2,3-diacetamido-2,3-dideoxygalacturonic acid (GalNAc3NAcA) in which some of the sugars are present as uronamides. The terminal residue contains several unusual modifications. To date, two types of modification have been characterized, and a survey of numerous strains demonstrated that each contained one of these two modification types. Host antibody responses against the O PS are directed against the terminal residue modifications, and there is little cross-reactivity between the two types. This suggests that Bordetella O PS modifications represent a means of antigenic variation. Here we report the characterization of the O PS of B. bronchiseptica strain MO149. It consists of a novel two-sugar repeating unit and a novel terminal residue modification, with the structure Me-4-␣-L-GalNAc3NAcA-(4-␤-D-GlcNAc3NAcA-4-␣-LGalNAc3NAcA-) 5-6 -, which we propose be defined as the B. bronchiseptica O3 PS. We show that the O3 PS is very poorly immunogenic and that the MO149 strain contains a novel wbm (O PS biosynthesis) locus. Thus, there is greater diversity among Bordetella O PSs than previously recognized, which is likely to be a result of selection pressure from host immunity. We also determine experimentally, for the first time, the absolute configuration of the diacetimido-uronic acid sugars in Bordetella O PS.The genus Bordetella currently comprises nine species of Gram-negative bacteria. The most extensively studied of these are the pathogens Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica. B. pertussis infects only humans and is the causative agent of whooping cough in infants and persistent respiratory infections in adults (1). B. parapertussis exists as two separate lineages. One is adapted to the human host and causes whooping cough; the other is adapted to the ovine host, in which it can cause chronic pneumonia (2, 3). In contrast, B. bronchiseptica colonizes the respiratory tract of a large number of animals, and although it causes respiratory diseases in some farm, companion, and wild animals, most B. bronchiseptica infections are asymptomatic and chronic (4). B. bronchiseptica is occasionally isolated from the respiratory tract of humans and is probably acquired through contact with infected animals (5).Bordetella lipopolysaccharide (LPS) plays a number of different roles in Bordetella biology, including during infection (e.g. see Refs. 6 -9). We and others have defined the structures of the LPS of these Bordetella (Fig. 1). All three synthesize a very similar LPS core. In B. bronchiseptica and B. pertussis, the core can be further substituted by a trisaccharide to produce the structure referred to as Band A LPS (10, 11). B. parapertussis and B. bronchiseptica, but not B. pertussis, synthesize O PSs.2 Initially, the O PSs of both species were reported to be identical and composed of linear polymers of 1,4-linked GalNAc3NAcA (12), but later it was disc...

Horizontally acquired divergent O-antigen contributes to escape from cross-immunity in the classical bordetellae

“…Bordetella O-antigen types were previously defined as O1- or O2- serotype based on cross-reactive antigenicity [ 17 ], but recently it was shown that B. bronchiseptica strain MO149 produces a poorly immunogenic O-antigen designated O3 [ 14 ]. This O-antigen, unlike O1 and O2, was not recognized by antibodies generated during infection, and did not cross-react with any Bordetella O1- or O2- serotype specific antibodies [ 14 - 16 ].…”

“…Bordetella O-antigen types were previously defined as O1- or O2- serotype based on cross-reactive antigenicity [ 17 ], but recently it was shown that B. bronchiseptica strain MO149 produces a poorly immunogenic O-antigen designated O3 [ 14 ]. This O-antigen, unlike O1 and O2, was not recognized by antibodies generated during infection, and did not cross-react with any Bordetella O1- or O2- serotype specific antibodies [ 14 - 16 ]. To assess the diversity of O-antigen antigenicity among the classical bordetellae, we examined more strains by purifying their LPS and probing with antibodies generated against LPS containing either O1-, O2-, or O3-type O-antigens ( B. bronchiseptica strain RB50, B. bronchiseptica strain 1289, or B. bronchiseptica strain MO149, respectively) (Figure 1 A-C).…”

“…The two remaining strains, Bpp5 and MO149, both differ from the other six strains in a region we have designated Variable Region B (VRB) (Figure 2 ). Strain MO149, the sole example of the poorly antigenic O3 type (Figure 1 C and D) [ 14 ], lacks VRA genes and has a set of genes in VRB that appear intact, but are either novel or highly divergent orthologs with as little as 50% similarity to reference strain genes (Figure 2 ). This set of genes is apparently sufficient to make a poorly antigenic O-antigen (Figure 1 C and D) [ 14 ].…”

“…Strain MO149, the sole example of the poorly antigenic O3 type (Figure 1 C and D) [ 14 ], lacks VRA genes and has a set of genes in VRB that appear intact, but are either novel or highly divergent orthologs with as little as 50% similarity to reference strain genes (Figure 2 ). This set of genes is apparently sufficient to make a poorly antigenic O-antigen (Figure 1 C and D) [ 14 ]. Strain Bpp5, which does not appear to make O-antigen, has a nearly complete VRA, but a highly divergent VRB, with several genes of low similarity to reference genes, one unique gene and two apparent pseudogenes.…”

“…In addition, several strains of B. parapertussis do not produce the trisaccharide, likely due to a mutation in the wlb locus, while B. pertussis does not produce an O-antigen due to the lack of the wbm locus [ 10 , 13 ]. The O-antigen locus in most B. bronchiseptica and B. parapertussis strains contains 24 genes, while the recently characterized wbm locus of one B. bronchiseptica strain (MO149) contains only 15 genes, most of which are genetically divergent from the previously characterized loci [ 1 , 4 , 10 , 14 ]. The first 14 genes within the O-antigen locus are thought to be responsible for the biosynthesis of the pentasaccharide linker region connecting the O-polysaccharide to the inner core, synthesis of the polymer subunit, and the capping sugar [ 10 , 11 , 15 ].…”