A high seroprevalence of antibodies to pertussis toxin among Japanese adults: Qualitative and quantitative analyses

In 2013, national serosurveillance detected a high seroprevalence of antibodies to pertussis toxin (PT) from Bordetella pertussis among Japanese adults. Thus, we aimed to determine the cause(s) of this high seroprevalence, and analyzed the titers of antibodies to PT and filamentous hemagglutinin (FHA) among adults (35-44 years old), young children (4-7 years old), and older children (10-14 years old). Our quantitative analyses revealed that adults had higher seroprevalences of anti-PT IgG and PT-neutralizing antibodies, and similar titers of anti-FHA IgG, compared to the young and older children. Positive correlations were observed between the titers of PT-neutralizing antibodies and anti-PT IgG in all age groups (rs values of 0.326-0.522), although the correlation tended to decrease with age. The ratio of PT-neutralizing antibodies to anti-PT IgG was significantly different when we compared the serum and purified IgG fractions among adults (p = 0.016), although this result was not observed among young and older children. Thus, it appears that some adults had non-IgG immunoglobulins to PT. Our analyses also revealed that adults had high-avidity anti-PT IgG (avidity index: 63.5%, similar results were observed among the children); however, the adults had lower-avidity anti-FHA IgG (37.9%, p < 0.05). It is possible that low-avidity anti-FHA IgG is related to infection with other respiratory pathogens (e.g., Bordetella parapertussis, Haemophilus influenzae, or Mycoplasma pneumoniae), which produces antibodies to FHA-like proteins. Our observations suggest that these adults had been infected with B. pertussis and other pathogen(s) during their adulthood.

Bordetella parapertussis Circumvents Neutrophil Extracellular Bactericidal Mechanisms

B. parapertussis is a whooping cough etiological agent with the ability to evade the immune response induced by pertussis vaccines. We previously demonstrated that in the absence of opsonic antibodies B. parapertussis hampers phagocytosis by neutrophils and macrophages and, when phagocytosed, blocks intracellular killing by interfering with phagolysosomal fusion. But neutrophils can kill and/or immobilize extracellular bacteria through non-phagocytic mechanisms such as degranulation and neutrophil extracellular traps (NETs). In this study we demonstrated that B. parapertussis also has the ability to circumvent these two neutrophil extracellular bactericidal activities. The lack of neutrophil degranulation was found dependent on the O antigen that targets the bacteria to cell lipid rafts, eventually avoiding the fusion of nascent phagosomes with specific and azurophilic granules. IgG opsonization overcame this inhibition of neutrophil degranulation. We further observed that B. parapertussis did not induce NETs release in resting neutrophils and inhibited NETs formation in response to phorbol myristate acetate (PMA) stimulation by a mechanism dependent on adenylate cyclase toxin (CyaA)-mediated inhibition of reactive oxygen species (ROS) generation. Thus, B. parapertussis modulates neutrophil bactericidal activity through two different mechanisms, one related to the lack of proper NETs-inducer stimuli and the other one related to an active inhibitory mechanism. Together with previous results these data suggest that B. parapertussis has the ability to subvert the main neutrophil bactericidal functions, inhibiting efficient clearance in non-immune hosts.

Host Specificity of Ovine Bordetella parapertussis and the Role of Complement

The classical bordetellae are comprised of three subspecies that differ from broad to very limited host specificity. Although several lineages appear to have specialized to particular host species, most retain the ability to colonize and grow in mice, providing a powerful common experimental model to study their differences. One of the subspecies, Bordetella parapertussis, is composed of two distinct clades that have specialized to different hosts: one to humans (Bpp_hu), and the other to sheep (Bpp_ov). While Bpp_hu and the other classical bordetellae can efficiently colonize mice, Bpp_ov strains are severely defective in their ability to colonize the murine respiratory tract. Bpp_ov genomic analysis did not reveal the loss of adherence genes, but substantial mutations and deletions of multiple genes involved in the production of O-antigen, which is required to prevent complement deposition on B. bronchiseptica and Bpp_hu strains. Bpp_ov lacks O-antigen and, like O-antigen mutants of other bordetellae, is highly sensitive to murine complement-mediated killing in vitro. Based on these results, we hypothesized that Bpp_ov failed to colonize mice because of its sensitivity to murine complement. Consistent with this, the Bpp_ov defect in the colonization of wild type mice was not observed in mice lacking the central complement component C3. Furthermore, Bpp_ov strains were highly susceptible to killing by murine complement, but not by sheep complement. These data demonstrate that the failure of Bpp_ov to colonize mice is due to sensitivity to murine, but not sheep, complement, providing a mechanistic example of how specialization that accompanies expansion in one host can limit host range.

[Seroprevalence of antibodies against lipopolysaccharides of Bordetella parapertussis in patients with prolonged caught in Poland]

INTRODUCTION

Bordetella parapertussis is a bacterium closely related to Bordetella pertussis, also causes a pertussis - like symptoms in humans. Because of unsatisfactory level of routine microbiological diagnosis of B. parapertussis infections in Poland most of parapertussis cases are not reported. The aim of the presented study was to investigate incidence of B. parapertussis in patients with cough in Poland using serology method.

METHODS

Serum IgA, IgG and IgM antibodies were determined in 1192 serum samples obtained from patients with respiratory infections and chronic cough and who were previously suspected of B. pertussis infection. As a control we used 258 sera from healthy people - blood donors. The LPS antigen was extracted by Westphal method from wild B. parapertussis strain isolated in Poland. For exclusion of possible false positive results with B. pertussis some of the sera were tested against the purified pertussis toxin (PT).

RESULTS

The diagnostically significant level of IgA antibodies to LPS of B. parapertussis was detected in 11.9%, IgG in 12.2% and IgM in 9.6% serum samples. More often the antibodies were diagnosed in women than in men. In 63 serum samples, previously positive in NovaTec ELISA with mixed antigen of pertussis toxin and filamentous hemagglutinin we found also IgA and IgG antibodies to LPS of B. parapertussis. However, after use of purified pertussis toxin antigen in ELISA we confirmed the B. pertussis infections only in 28 cases.

CONCLUSIONS

This study shows that B. parapertussis is a serious causative agent of infections in patients with prolonged caught in Poland. The serodiagnosis ofparapertussis should be conducted with sera obtained from patients suspected in clinical investigation for pertussis but negative in serological investigation with purified pertussis toxin antigen.

O antigen allows B. parapertussis to evade B. pertussis vaccine-induced immunity by blocking binding and functions of cross-reactive antibodies

Although the prevalence of Bordetella parapertussis varies dramatically among studies in different populations with different vaccination regimens, there is broad agreement that whooping cough vaccines, composed only of B. pertussis antigens, provide little if any protection against B. parapertussis. In C57BL/6 mice, a B. pertussis whole-cell vaccine (wP) provided modest protection against B. parapertussis, which was dependent on IFN-γ. The wP was much more protective against an isogenic B. parapertussis strain lacking O-antigen than its wild-type counterpart. O-antigen inhibited binding of wP–induced antibodies to B. parapertussis, as well as antibody-mediated opsonophagocytosis in vitro and clearance in vivo. aP–induced antibodies also bound better in vitro to the O-antigen mutant than to wild-type B. parapertussis, but aP failed to confer protection against wild-type or O antigen–deficient B. parapertussis in mice. Interestingly, B. parapertussis–specific antibodies provided in addition to either wP or aP were sufficient to very rapidly reduce B. parapertussis numbers in mouse lungs. This study identifies a mechanism by which one pathogen escapes immunity induced by vaccination against a closely related pathogen and may explain why B. parapertussis prevalence varies substantially between populations with different vaccination strategies.

The O antigen enables Bordetella parapertussis to avoid Bordetella pertussis-induced immunity

Bordetella pertussis and Bordetella parapertussis are closely related endemic human pathogens which cause whooping cough, a disease that is reemerging in human populations. Despite how closely related these pathogens are, their coexistence and the limited efficacy of B. pertussis vaccines against B. parapertussis suggest a lack of cross-protective immunity between the two. We sought to address the ability of infection-induced immunity against one of these pathogens to protect against subsequent infection by the other using a mouse model of infection. Immunity induced by B. parapertussis infection protected against subsequent infections by either species. However, immunity induced by B. pertussis infection prevented subsequent B. pertussis infections but did not protect against B. parapertussis infections. The O antigen of B. parapertussis inhibited binding of antibodies to the bacterial surface and was required for B. parapertussis to colonize mice convalescent from B. pertussis infection. Thus, the O antigen of B. parapertussis confers asymmetrical cross-immunity between the causative agents of whooping cough. We propose that these findings warrant investigation of the relative role of B. parapertussis in the resurgence of whooping cough.

Comparative role of immunoglobulin A in protective immunity against the Bordetellae

The genus Bordetella includes a group of closely related mammalian pathogens that cause a variety of respiratory diseases in a long list of animals (B. bronchiseptica) and whooping cough in humans (B. pertussis and B. parapertussis). While past research has examined how these pathogens are eliminated from the lower respiratory tract, the host factors that control and/or clear the bordetellae from the upper respiratory tract remain unclear. We hypothesized that immunoglobulin A (IgA), the predominant mucosal antibody isotype, would have a protective role against these mucosal pathogens. IgA(-/-) mice were indistinguishable from wild-type mice in their control and clearance of B. pertussis or B. parapertussis, suggesting that IgA is not crucial to immunity to these organisms. However, naïve and convalescent IgA(-/-) mice were defective in reducing the numbers of B. bronchiseptica in the upper respiratory tract compared to wild-type controls. Passively transferred serum from convalescent IgA(-/-) mice was not as effective as serum from convalescent wild-type mice in clearing this pathogen from the tracheae of naive recipient mice. IgA induced by B. bronchiseptica infection predominantly recognized lipopolysaccharide-containing O-antigen, and antibodies against O-antigen were important to bacterial clearance from the trachea. Since an IgA response contributes to the control of B. bronchiseptica infection of the upper respiratory tract, immunization strategies aimed at inducing B. bronchiseptica-specific IgA may be beneficial to preventing the spread of this bacterium among domestic animal populations.

Use of a genetically defined double mutant strain of Bordetella bronchiseptica lacking adenylate cyclase and type III secretion as a live vaccine

While most vaccines consisting of killed bacteria induce high serum antibody titers, they do not always confer protection as effective as that induced by infection, particularly against mucosal pathogens. Bordetella bronchiseptica is a gram-negative respiratory pathogen that is endemic in many nonhuman mammalian populations and causes substantial disease in a variety of animals. At least 14 different live attenuated vaccines against this pathogen are available for use in a variety of livestock and companion animals. However, there are few published data on the makeup or efficacy of these vaccines. Here we report the use of a genetically engineered double mutant of B. bronchiseptica, which lacks adenylate cyclase and type III secretion, as a vaccine candidate. This strain is safe at high doses, even for highly immunocompromised animals, and induces immune responses that are protective against highly divergent B. bronchiseptica strains, preventing colonization in the lower respiratory tract and decreasing the bacterial burden in the upper respiratory tract. This novel B. bronchiseptica vaccine candidate induces strong local immunity while eliminating damage caused by the two predominant cytotoxic mechanisms.

Characterization of serological responses to pertussis

We have compared the use of five nonvaccine antigens to the use of conventional vaccine antigens, pertussis toxin (PT), and filamentous hemagglutinin (FHA) for the serological diagnosis of pertussis by enzyme-linked immunosorbent assay (ELISA). The nonvaccine antigens included the catalytic region of adenylate cyclase toxin (CatACT), the C-terminal region of FHA (C-FHA), lipooligosaccharide (LOS), the peptidoglycan-associated lipoprotein (PAL), and the BrkA protein. The serological responses of individuals with culture-confirmed pertussis were compared to those of adults with no recent history of a coughing disease. An immunoglobulin G (IgG) ELISA for PT was the most sensitive (92.2%) test for the serodiagnosis of pertussis. Of the nonvaccine antigens, ELISA for IgG responses to CatACT (sensitivity, 62.8%), C-FHA (sensitivity, 39.2%), and LOS IgA (sensitivity, 29.4%) were less sensitive but could also distinguish culture-positive individuals from control individuals. The use of a combination of multiple ELISA targets improved the sensitivity of the assay for serological diagnosis. Elevated IgG and IgA antibody titers persisted for more than a year in the individuals with culture-confirmed pertussis.

Infección por Bordetella spp.: 19 años de diagnóstico por cultivo

INTRODUCTION

This retrospective study reviews the findings from cultures positive for Bordetella spp. obtained over a 19-year period, from January 1984 to December 2002.

METHODS

Nasopharyngeal swabs were directly plated onto charcoal agar supplemented with 10% sheep blood and cephalexin (40 mg/L). Identification of suspected colonies was done by biochemical testing and slide agglutination with specific antisera for B. pertussis and B. parapertussis. The study includes microbiological findings and epidemiological data (age, sex, yearly distribution, seasonal period and number of inpatients and outpatients).

RESULTS

The 2064 nasopharyngeal specimens yielded 269 positive cultures: B. pertussis was isolated from 244 patients, B. parapertussis from 23 and B. bronchiseptica from two. Among the positive patients, 36.9% were younger than 7 months, 38.8% were 7 months to 6 years old and 24.3% were older than 6 years of age.

CONCLUSIONS

The constant number of cases along the 19 years of the study shows that Bordetella spp. continues to circulate in our area. A high percentage of positive cultures were obtained from the group of children theoretically immunized by vaccination. Despite the low number of cases in young people and adults, adult pertussis seems to be a greater public health threat than was previously suspected and probably deserves to be further investigated. The gold standard for the diagnosis of Bordetella spp. infection is still recovery of the organism by culture, and it is especially useful for confirming outbreaks.