Antigenic analysis of the saccharide moiety of the lipooligosaccharide of Bordetella pertussis

Activation of the complement cascade by Bordetella pertussis

Bordetella pertussis must survive the defenses of the human respiratory tract including the complement system. The BrkA (Bordetella resistance to killing) protein prevents killing by the antibody-dependent classical pathway. In this study, the ability of B. pertussis to activate the human complement cascade by other pathways was examined. B. pertussis was not killed in serum depleted of C2, however serum depleted for factor B killed B. pertussis as efficiently as intact serum, suggesting complement activation occurred exclusively by the classical pathway. B. pertussis was not killed by serum depleted of antibody, suggesting the bacteria fail to activate the antibody-independent branches of the classical pathway, including the mannose binding lectin pathway. Mutants lacking the terminal trisaccharide of lipopolysaccharide retained the complement-resistant phenotype, suggesting this structure does not influence activation of complement.

Pertussis toxin and lipopolysaccharide influence phagocytosis of Bordetella pertussis by human monocytes

The potential of human monocytes to mediate the clearance of Bordetella pertussis infection was examined. Bacteria expressing green fluorescent protein were incubated with adherent peripheral blood monocytes, and phagocytosis was quantified by using fluorescence microscopy. Monocytes internalized only a small percentage of the adherent bacteria. Surface-associated Bvg-regulated virulence factors, including adenylate cyclase toxin and filamentous hemagglutinin, did not affect attachment or phagocytosis. However, 1-h pretreatment with purified pertussis toxin inhibited the ability of monocytes to internalize wild-type bacteria. Mutations affecting the terminal trisaccharide of lipopolysaccharide resulted in reduced internalization without affecting adherence of bacteria to monocytes. Opsonization with human serum played only a modest role in promoting phagocytosis. The viability of internalized bacteria was determined by colony counts following treatment with polymyxin B and gentamicin. Less than 1% of internalized bacteria remained viable. These results suggest that pertussis toxin plays a role in the evasion of monocyte phagocytosis and that these cells represent a potential mediator of the clearance of B. pertussis infection.

Role of antibodies against Bordetella pertussis virulence factors in adherence of Bordetella pertussis and Bordetella parapertussis to human bronchial epithelial cells

Immunization with whole-cell pertussis vaccines (WCV) containing heat-killed Bordetella pertussis cells and with acellular vaccines containing genetically or chemically detoxified pertussis toxin (PT) in combination with filamentous hemagglutinin (FHA), pertactin (Prn), or fimbriae confers protection in humans and animals against B. pertussis infection. In an earlier study we demonstrated that FHA is involved in the adherence of these bacteria to human bronchial epithelial cells. In the present study we investigated whether mouse antibodies directed against B. pertussis FHA, PTg, Prn, and fimbriae, or against two other surface molecules, lipopolysaccharide (LPS) and the 40-kDa outer membrane porin protein (OMP), that are not involved in bacterial adherence, were able to block adherence of B. pertussis and B. parapertussis to human bronchial epithelial cells. All antibodies studied inhibited the adherence of B. pertussis to these epithelial cells and were equally effective in this respect. Only antibodies against LPS and 40-kDa OMP affected the adherence of B. parapertussis to epithelial cells. We conclude that antibodies which recognize surface structures on B. pertussis or on B. parapertussis can inhibit adherence of the bacteria to bronchial epithelial cells, irrespective whether these structures play a role in adherence of the bacteria to these cells.

Characterization of human bactericidal antibodies to Bordetella pertussis

The Bordetella pertussis BrkA protein protects against the bactericidal activity of complement and antibody; however, some individuals mount an immune response that overcomes this bacterial defense. To further characterize this process, the bactericidal activities of sera from 13 adults with different modes of exposure to B. pertussis (infected as adults, occupational exposure, immunized with an acellular vaccine, or no identified exposure) against a wild-type strain and a BrkA complement-sensitive mutant were evaluated. All of the sera killed the BrkA mutant, suggesting past exposure to B. pertussis or cross-reactive organisms. Several samples had no or minimal activity against the wild type. All of the sera collected from the infected and occupationally exposed individuals but not all of the sera from vaccinated individuals had bactericidal activity against the wild-type strain, suggesting that some types of exposure can induce an immune response that can overcome the BrkA resistance mechanism. Adsorbing serum with the wild-type strain removed the bactericidal antibodies; however, adsorbing the serum with a lipopolysaccharide (LPS) mutant or an avirulent (bvg mutant) strain did not always result in loss of bactericidal activity, suggesting that antibodies to either LPS or bvg-regulated proteins could be bactericidal. All the samples, including those that lacked bactericidal activity, contained antibodies that recognized the LPS of B. pertussis. Bactericidal activity correlated best with the presence of the immunoglobulin G3 (IgG3) antibodies to LPS, the IgG subtype that is most effective at fixing complement.

Evaluation and validation of a monoclonal immunofluorescent reagent for direct detection of Bordetella pertussis

An outbreak of pertussis in Manitoba, Canada, provided an opportunity to evaluate the recently developed monoclonal antibody (MAb) BL-5 for the direct detection of Bordetella pertussis. The MAb recognizes a lipooligosaccharide epitope. A total of 1,507 consecutive nasopharyngeal swabs for culture and companion smears for direct fluorescent-antibody (DFA) detection were evaluated at Cadham Provincial Laboratory between September and November 1994. The cutoff for DFA positivity was four fluorescing organisms with morphology characteristic of B. pertussis. PCR analysis for B. pertussis DNA was performed on a subset of 100 smears by eluting material from the slides after DFA examination. In comparison with culture, the sensitivity, specificity, and positive and negative predictive values of BL-5 were 65.1% (41 of 63 samples), 99.6% (1,438 of 1,444 samples), 87.2% (41 of 47 samples), and 98.5% (1,438 of 1,460 samples), respectively. The sensitivity of culture compared with PCR was 45.5% (10 of 22 samples) for the subset of 100 specimens tested by both procedures. An expanded "gold standard" of positivity by culture or PCR for these 100 specimens resulted in DFA sensitivity, specificity, and positive and negative predictive values of 32.3, 97.1, 83.3, and 76.1%, respectively. The utility of MAb BL-5 for direct detection of B. pertussis in a clinical laboratory setting has been demonstrated by this investigation.

Analysis of protective and nonprotective monoclonal antibodies specific for Bordetella pertussis lipooligosaccharide

In this study, it has been determined that immunoglobulin G1 (IgG1) and IgG3 monoclonal antibodies directed to the lipooligosaccharide A of Bordetella pertussis were able to protect mice from fatal aerosol infection. No correlation was found between the bactericidal activity in vitro in the presence of complement and the protection in mice, since a bactericidal IgG3 did not elicit protection. In addition, no significant difference in protective capacity was observed with bactericidal and nonbactericidal IgG1 antibodies, indicating that bactericidal activity is not a requirement for protection mediated by certain anti-lipooligosaccharide A antibodies. A reduction in protection in C5-deficient mice was observed, suggesting a significant role for complement in certain host defense mechanisms against B. pertussis infection.