Transmission of Bordetella pertussis to young infants

BACKGROUND

Pertussis vaccination has reduced the number of notified cases in industrialized countries from peak years by more than 95%. The effect of recently recommended adult and adolescent vaccination strategies on infant pertussis depends, in part, on the proportion of infants infected by adults and adolescents. This proportion, however, remains unclear, because studies have not been able to determine the source case for 47%-60% of infant cases.

METHODS

A prospective international multicenter study was conducted of laboratory confirmed infant pertussis cases (aged <or=6 months) and their household and nonhousehold contacts. Comprehensive diagnostic evaluation (including PCR and serology) was performed on all participants independent of symptoms. Source cases were identified and described by relationship to the infant, age and household status.

RESULTS

The study population comprised 95 index cases and 404 contacts. The source of pertussis was identified for 48% of infants in the primary analysis and up to 78% in sensitivity analyses. In the primary analysis, parents accounted for 55% of source cases, followed by siblings (16%), aunts/uncles (10%), friends/cousins (10%), grandparents (6%) and part-time caretakers (2%). The distribution of source cases was robust to sensitivity analyses.

CONCLUSIONS

This study provides solid evidence that among infants for whom a source case was identified, household members were responsible for 76%-83% of transmission of Bordetella pertussis to this high-risk group. Vaccination of adolescents and adults in close contact with young infants may thus eliminate a substantial proportion of infant pertussis if high coverage rates can be achieved.

The concept of pertussis as a toxin-mediated disease

Pertussis (whooping cough), a two-stage process of disease (respiratory colonization and toxin-mediated disease) is caused by B. pertussis. The bacterium is unique. It is a pathogenic parasite with habitat only in human beings. Growth in the pathogenic form, both in in vitro and in vivo, requires conditions that permit the expression of pertussis toxin (PT) (also known as histamine-sensitizing factor, lymphocyte-leukocyte-promoting factor, islet-activating factor and pertussigen). The expression of growth and PT appear to be genetically interrelated. For multiplication in vitro the medium must be free of substances, such as fatty acids, that inhibit the enzymatic action required for elaboration of PT. In vivo the bacteria are uniquely localized to the cilia of the respiratory epithelium where they multiply. In situ the bacteria inhibit natural defenses of the respiratory tract (cilial, phagocytic and other activities); they tend not to spread and do not invade the underlying tissue. The extent of the areas of colonization, directly related to the number of bacteria in the infecting inoculum, influences the amount of toxin elaborated and consequently the intensity of the clinical symptoms. Other factors that influence the clinical disease are the inordinate susceptibility of the infant and genetically controlled susceptibility. A specific role for PT in the initial establishment of the infection is not clear, but it seems definite that PT-specific immunity influences the clearance of colonization in about 4 to 5 weeks. The clinical symptoms become manifest when the bacteria are waning. This clearance is influenced by the synthesis of IgA antibodies and pertussis toxin antibodies that may act by inhibiting the "enzyme" required for growth or by another mechanism. The pathology of the disease is the result of altered cellular functions of toxin-sensitized cells, not by histologic damage. PT is composed of two functional components like other exotoxins that cause infectious disease (e.g. diphtheria, cholera). Certain sites on one component enable PT to bind to specific receptors on tissue cells and enter the cell. The toxin ADP ribosylates a regulatory protein of the cytoplasmic membrane and thereby alters the function of the cell. Affected (sensitized) cells are insulin-secretory islets of the pancreas, lymphocytes and leukocytes, heart cells and others that have not been clearly identified, e.g. those that effect paroxysms and neurologic disturbances. The altered function of the cell in vitro is irreversible, and the restoration of the function of a particular tissue in vivo appears to be dependent on the renewal of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Atypical disease after Bordetella pertussis respiratory infection of mice with targeted disruptions of interferon-gamma receptor or immunoglobulin mu chain genes

Using a murine respiratory challenge model we have previously demonstrated a role for Th1 cells in natural immunity against Bordetella pertussis, but could not rule out a role for antibody. Here we have demonstrated that B. pertussis respiratory infection of mice with targeted disruptions of the genes for the IFN-gamma receptor resulted in an atypical disseminated disease which was lethal in a proportion of animals, and was characterized by pyogranulomatous inflammation and postnecrotic scarring in the livers, mesenteric lymph nodes and kidneys. Viable virulent bacteria were detected in the blood and livers of diseased animals. An examination of the course of infection in the lung of IFN-gamma receptor-deficient, IL-4-deficient and wild-type mice demonstrated that lack of functional IFN-gamma or IL-4, cytokines that are considered to play major roles in regulating the development of Th1 and Th2 cells, respectively, did not affect the kinetics of bacterial elimination from the lung. In contrast, B cell-deficient mice developed a persistent infection and failed to clear the bacteria after aerosol inoculation. These findings demonstrate an absolute requirement for B cells or their products in the resolution of a primary infection with B. pertussis, but also define a critical role for IFN-gamma in containing bacteria to the mucosal site of infection.

The transcriptional responses of respiratory epithelial cells to Bordetella pertussis reveal host defensive and pathogen counter-defensive strategies

Bordetella pertussis, the causative agent of whooping cough, has many well-studied virulence factors and a characteristic clinical presentation. Despite this information, it is not clear how B. pertussis interaction with host cells leads to disease. In this study, we examined the interaction of B. pertussis with a human bronchial epithelial cell line (BEAS-2B) and measured host transcriptional profiles by using high-density DNA microarrays. The early transcriptional response to this pathogen is dominated by altered expression of cytokines, DNA-binding proteins, and NFkappaB-regulated genes. This previously unrecognized response to B. pertussis was modified in similar but nonidentical fashions by the antiinflammatory agents dexamethasone and sodium salicylate. Cytokine protein expression was confirmed, as was neutrophil chemoattraction. We show that B. pertussis induces mucin gene transcription by BEAS-2B cells then counters this defense by using mucin as a binding substrate. A set of genes is described for which the catalytic activity of pertussis toxin is both necessary and sufficient to regulate transcription. Host genomic transcriptional profiling, in combination with functional assays to evaluate subsequent biological events, provides insight into the complex interaction of host and pathogen.

Role of adenylate cyclase-hemolysin in alveolar macrophage apoptosis during Bordetella pertussis infection in vivo

Bordetella pertussis induces in vitro apoptosis of murine alveolar macrophages by a mechanism that is dependent on expression of bacterial adenylate cyclase-hemolysin. Using a murine respiratory model, we found in this study that intranasal infection with a parental B. pertussis strain, but not with an isogenic variant deficient in the expression of all toxins and adhesins, induced a marked neutrophil accumulation in the bronchoalveolar lavage fluid and an early decrease in macrophage numbers. These phenomena paralleled a time-dependent rise in the proportion of apoptotic nuclei, as detected by flow cytometry, and of macrophages which had engulfed apoptotic bodies. Apoptotic death of bronchopulmonary cells was observed exclusively following intranasal infection with bacteria reisolated from lungs of infected animals and not with B. pertussis collected after in vitro subculture. Using the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling technique coupled to fluorescence microscopy and morphological analysis, we established that the apoptotic cells in bronchoalveolar lavage fluids were neutrophils and macrophages. Histological analysis of the lung tissues from B. pertussis-infected mice showed increased numbers of apoptotic cells in the alveolar compartments. Cellular accumulation in bronchoalveolar lavage fluids and apoptosis of alveolar macrophages were significantly attenuated in mice infected with a mutant deficient in the expression of adenylate cyclase-hemolysin, indicating a role of this enzyme in these processes.

Modulation of innate and acquired immune responses by Escherichia coli heat-labile toxin: distinct pro- and anti-inflammatory effects of the nontoxic AB complex and the enzyme activity

We have examined the roles of enzyme activity and the nontoxic AB complex of heat-labile toxin (LT) from Escherichia coli on its adjuvant and immunomodulatory properties. LTK63, an LT mutant that is completely devoid of enzyme activity, enhanced Th1 responses to coinjected Ags at low adjuvant dose. In contrast, LTR72, a partially detoxified mutant, enhanced Th2 responses and when administered intranasally to mice before infection with Bordetella pertussis suppressed Th1 responses and delayed bacterial clearance from the lungs. LTR72 or wild-type LT inhibited Ag-induced IFN-gamma production by Th1 cells, and LT enhanced IL-5 production by Th2 cells in vitro. Each of the toxins enhanced B7-1 expression on macrophages, but enhancement of B7-2 expression was dependent on enzyme activity. We also observed distinct effects of the nontoxic AB complex and enzyme activity on inflammatory cytokine production. LT and LTR72 suppressed LPS and IFN-gamma induced TNF-alpha and IL-12 production, but enhanced IL-10 secretion by macrophages in vitro and suppressed IL-12 production in vivo in a murine model of LPS-induced shock. In contrast, LTK63 augmented the production of IL-12 and TNF-alpha. Furthermore, LTK63 enhanced NF-kappaB translocation, whereas low doses of LTR72 or LT failed to activate NF-kappaB, but stimulated cAMP production. Thus, E. coli LT appears to be capable of suppressing Th1 responses and enhancing Th2 responses through the modulatory effects of enzyme activity on NF-kappaB activation and IL-12 production. In contrast, the nontoxic AB complex can stimulate acquired immune responses by activating components of the innate immune system.

Characterization of murine lung inflammation after infection with parental Bordetella pertussis and mutants deficient in adhesins or toxins

Bordetella pertussis expresses factors such as filamentous hemagglutinin, agglutinogens, pertactin, and pertussis toxin, which participate in bacterial adhesion; pertussis toxin, dermonecrotic toxin, lipopolysaccharide, and tracheal cytotoxin, which are responsible for toxic effects; and adenylate cyclase-hemolysin, which is required to initiate infection. By using a murine respiratory model, we showed that the RGD sequences of filamentous hemagglutinin and pertactin are important for bacterial persistence. However, mutants deficient in filamentous hemagglutinin and agglutinogens or in pertactin and the RGD sequence of filamentous hemagglutinin behaved as did wild-type B. pertussis, i.e., induced bronchopneumonia, alveolitis, and an influx of macrophages, lymphocytes, and polymorphonuclear leukocytes into bronchoalveolar lavage fluids. These results suggest that these adhesins are not involved in the induction of pulmonary lesions following infection. The intensity of inflammation was markedly reduced after infection with mutants deficient in either hemolytic activity or pertussis toxin expression, whereas a mutant devoid of adenylate cyclase activity behaved as did the avirulent mutant. Pertussis toxin and adenylate cyclase-hemolysin may act indirectly by altering immune cell functions and thus allowing other factors, such as filamentous hemagglutinin, agglutinogens, and pertactin, to trigger adhesion and lipopolysaccharide, dermonecrotic toxin, and tracheal cytotoxin to induce their toxic effects. However, it is possible that pertussis toxin is also responsible for the induction of some pulmonary alterations.

Intranasal immunization with outer membrane vesicle pertussis vaccine confers broad protection through mucosal IgA and Th17 responses

A vaccine based on outer membrane vesicles of pertussis (omvPV) is protective in a mouse-challenge model and induces a broad antibody and mixed Th1/Th2/Th17 response against multiple antigens following subcutaneous immunization. However, this route did not result in mucosal immunity and did not prevent nasopharyngeal colonization. In this study, we explored the potential of intranasal immunization with omvPV. Only intranasal immunization induced strong mucosal immune responses that encompasses enhanced pulmonary and nasal IgA antibody levels, mainly directed against Vag8 and LPS. Furthermore, high numbers of IgA- and IgG-producing plasma cells were detected as well as lung-resident IgA memory B-cells. Finally, only intranasal immunization induced pulmonary Th1/Th17-related cytokine responses. The magnitude and type of systemic immunity was comparable between both routes and included high systemic IgG antibody levels, strong IgG-producing plasma cell responses, memory B-cells residing in the spleen and systemic Th1/Th2/Th17-related cytokine responses. Importantly, only intranasal immunization prevented colonization in both the lungs and the nasal cavity. In conclusion, intranasal omvPV immunization induces mucosal IgA and Th17-mediated responses without influencing the systemic immunity profile. These responses resulted in prevention of Bordetella pertussis colonization in the respiratory tract, including the nasal cavity, thereby potentially preventing transmission.

Compartmentalization of T cell responses following respiratory infection with Bordetella pertussis: hyporesponsiveness of lung T cells is associated with modulated expression of the co-stimulatory molecule CD28

We have used a murine respiratory challenge model to examine the local T cell responses in the lung during infection with Bordetella pertussis. T cells from lung parenchyma and airways of naive and infected mice were refractory to both antigen and mitogen stimulation in the presence of lung macrophages. Furthermore irradiated mononuclear cells from the lungs suppressed antigen and mitogen-induced proliferation, but not IFN-gamma production, by splenic T cells. Removal of macrophages and stimulation of purified lung T cells in the presence of irradiated splenic antigen-presenting cells fully restored the response to mitogen. However, T cells purified from the lung during the acute phase of infection with B. pertussis failed to proliferate or produce detectable levels of IL-2, IL-4, IL-5 or IFN-gamma in response to purified bacterial antigens. In contrast, splenic T cells from these animals produced high levels of IL-2 and IFN-gamma and proliferated strongly to a range of bacterial components. Phenotypic analysis of bronchoalveolar lavage cells during the course of infection revealed transient infiltration of neutrophils, followed by macrophages, CD4+ T cells and smaller numbers of CD8+ T cells and gammadelta+ T cells. Cell surface expression of B7 on infiltrating macrophages and CTLA-4 on T cells did not change significantly during infection. However, expression of the CD28 co-stimulatory molecule was profoundly reduced on lung T cells during the acute phase of infection. In contrast, lung T cells from mice primed by B. pertussis infection or vaccination were resistant to CD28 down-regulation. These results suggest compartmentalization of T cell responses between the lung and the periphery during B. pertussis infection and that B. pertussis may have immunomodulatory properties on local T cell populations in the lungs of naive mice.

Infection of newborn piglets with Bordetella pertussis: a new model for pertussis

Bordetella pertussis is the causative agent of pertussis or whooping cough. This bacterium is a human pathogen that under experimental conditions also infects selected rodents and primates. Here, we show for the first time that newborn piglets can be infected with B. pertussis when it is delivered intrapulmonarily. Infected piglets displayed fever and respiratory symptoms, such as nasal discharge, nonparoxysmal coughing, and breathing difficulties. Eventually, all infected animals developed severe bronchopneumonia, which in some cases was combined with a fibrinous pleuritits. Immunohistochemical staining revealed the presence of large numbers of B. pertussis cells within airways, adhering to the epithelial lining or phagocytosed by macrophages and neutrophils. Viable bacteria were reisolated from bronchoalveolar lavages and lung lesions for more than 10 days postinfection. The systemic presence of pertussis toxin was shown by hypoglycemia, lymphocytosis, and induction of a clustered pattern of CHO cells by serum and bronchoalveolar lavage samples. Thus, a large-animal model for pertussis was developed, which should complement existing rodent models for identifying the immune responses relevant to the design of new vaccines. In particular, this model should help researchers analyze the roles of both maternal and mucosal immunity in disease protection against pertussis and should ultimately assist in the design of new vaccines for early life protection.

Pathogenesis of infection with Bordetella pertussis in hamster tracheal organ culture

Hamster tracheal organ culture was employed as a model for study of the pathogenesis of infection due to Bordetella pertussis. Infected tracheal explants were examined with light, immunofluorescence, and electrom microscopy. B. pertussis organisms preferentially attached to the ciliated cells, producing ciliostasis and marked destruction of the subcellular organelles followed by expulsion of these cells from the epithelial layer. Other nonciliated respiratory epithelial cells appeared to be unaffected. Metabolic studies on infected tracheal cultrues indicated that significant deficiencies in syntheiss of host cell protein accompanied early cytopathology. Similarities and differences in host cell and parasite interaction were noted between B. pertussis and other pathogenic agents studied in this system.

Extracorporeal life support in pertussis

Severe B. pertussis infection in infants is characterized by severe respiratory failure, pulmonary hypertension, leukocytosis, and death. This retrospective case analysis highlights the course and outcome of severe B. pertussis infection treated with extracorporeal membrane oxygenation (ECMO) at a single center. Over the last decade, out of a total caseload of nearly 800 infants and children, 12 infants with severe B. pertussis have been referred for ECMO therapy to our center. All infants with pertussis infection who received ECMO therapy were less than 3 months of age at presentation and unvaccinated. There was a high mortality rate (7 of 12 infants died), which was associated with an elevated neutrophil count at presentation and multiorgan dysfunction characterized by intractable pulmonary hypertension, persistent systemic hypotension, renal insufficiency, and fits. ECMO should be offered to children with pertussis infection and respiratory failure refractory to mechanical ventilation. However, further research is required to determine the optimal management for infants receiving ECMO therapy with this disease.

Sequence variation in pertussis S1 subunit toxin and pertussis genes in Bordetella pertussis strains used for the whole-cell pertussis vaccine produced in Poland since 1960: efficiency of the DTwP vaccine-induced immunity against currently circulating B. pertussis isolates

The present study indicates that the appearance of the B. pertussis harbouring prn2 gene allele variant (not found among clinical isolates before 1990s) may have been induced by long-term vaccination in Poland with DTP-composed vaccine strains presenting exclusively prn1. However, ptxS1A allele of pertussis toxin subunit S1 encoding gene, predominant in the currently isolated B. pertussis strains, has been found in vaccine strains used for whole-cell pertussis component (wP) production of DTP vaccine in 1960-1978. This outrules the possibility that the appearance of ptxSIA allele might be related to vaccine pressure driven by non-ptxS1A vaccine strains used for long-term immunization with wP. Intranasal challenge animal model testing the efficiency of the clearance of B. pertussis strains harbouring different ptxS1/prn allele gene combinations revealed that currently produced DTwP vaccine may not contain adequate B. pertussis vaccine strains, since isolates with gene variants different from those observed in vaccine strains were eliminated from the lungs of the immunized animals with lower efficiency.

ECLS in pertussis: does it have a role?

OBJECTIVES

To investigate the value of extracorporeal circulatory life support (ECLS) in paediatric patients with severe Bordetella pertussis infection.

DESIGN

Single case report and a review of the ECLS database.

SETTING

Tertiary referral hospital paediatric intensive care unit.

PATIENTS AND PARTICIPANTS

A single case report of an infant with B. pertussis infection is described. Despite receiving ECLS, this infant died from overwhelming cardiac and cerebral insults. Outcome for children receiving ECLS registered on the Extracorporeal Life Support Organization database is reviewed.

MEASUREMENTS AND RESULTS

The mortality of infants receiving ECLS for B. pertussis infection is high, with only 5 survivors reported among 22 registered cases. The majority of nonsurvivors had evidence of circulatory collapse in addition to severe respiratory failure, and these patients commonly died of hypoxic-ischaemic cerebral insult. These data suggest the existence of a subgroup of patients with respiratory failure only, who may benefit from ECLS, and a larger subgroup who suffer ischaemic cardiac and cerebral insults which are unlikely to be improved by ECLS.

CONCLUSIONS

The value of ECLS in patients with B. pertussis infection who present with major cardiac dysfunction is questionable. Such patients almost invariably have a poor outcome despite maximal therapy.

Host genetics of Bordetella pertussis infection in mice: significance of Toll-like receptor 4 in genetic susceptibility and pathobiology

The susceptibility to and the severity of Bordetella pertussis infections in infants and children varies widely, suggesting that genetic differences between individuals influence the course of infection. We have previously identified three novel loci that influence the severity of whooping cough by using recombinant congenic strains of mice: Bordetella pertussis susceptibility loci 1, 2, and 3 (Bps1, -2, and -3). Because these loci could not account for all genetic differences between mice, we extended our search for additional susceptibility loci. We therefore screened 11 inbred strains of mice for susceptibility to a pertussis infection after intranasal infection. Susceptibility was defined by the number of bacteria in the lungs, being indicative of the effect between the clearance and replication of bacteria. The most resistant (A/J) and the most susceptible (C3H/HeJ) strains were selected for further genetic and phenotypic characterization. The link between bacterial clearance and chromosomal location was investigated with 300 F2 mice, generated by crossing A/J and C3H/HeJ mice. We found a link between the delayed clearance of bacteria from the lung and a large part of chromosome 4 in F2 mice with a maximum log of the odds score of 33.6 at 65.4 Mb, which is the location of Tlr4. C3H/HeJ mice carry a functional mutation in the intracellular domain of Tlr4. This locus accounted for all detectable genetic differences between these strains. Compared to A/J mice, C3H/HeJ mice showed a delayed clearance of bacteria from the lung, a higher relative lung weight, and increased body weight loss. Splenocytes from infected C3H/HeJ mice produced almost no interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) upon ex vivo restimulation with B. pertussis compared to A/J mice and also showed a delayed gamma interferon (IFN-gamma) production. TNF-alpha expression in the lungs 3 days after infection was increased fivefold compared to uninfected controls in A/J mice and was not affected in C3H/HeJ mice. In conclusion, Tlr4 is a major host factor explaining the differences in the course of infection between these inbred strains of mice. Functional Tlr4 is essential for an efficient IL-1-beta, TNF-alpha, and IFN-gamma response; efficient clearance of bacteria from the lung; and reduced lung pathology.

Bordetella pertussis Infection in Infants and Young Children in Shanghai, China, 2016-2017: Clinical Features, Genotype Variations of Antigenic Genes and Macrolides Resistance

BACKGROUND

The global resurgence of pertussis in countries with high vaccination coverage has been a concern of public health.

METHODS

Nasopharyngeal swabs were collected for Bordetella pertussis culture from children with suspected pertussis. Clinical and vaccination information were reviewed through electronic medical chart and immunization record. Antibiotics susceptibility was evaluated using E-test for erythromycin, azithromycin, clarithromycin and sulfamethoxazole/trimethoprim. The MLST genotypes and 7 antigenic genes (ptxP, ptxA, ptxC, Prn, fim3, fim2 and tcfA) of Bordetella pertussis were identified by polymerase chain reaction amplification and sequencing.

RESULTS

During January 2016 to September 2017, a total of 141 children 1-48 months of age were culture-confirmed with pertussis, of whom 98 (69.5%) were younger than 6 months, 25 (17.7%) had completed at least 3 doses of DTaP and 75 (53.2%) had a clear exposure to household members with persistent cough. Fully vaccinated cases manifested milder disease than unvaccinated and not-fully vaccinated cases. All strains were MLST2. High-virulent strains characteristic of ptxP3/prn2/ptxC2 constituted 41.1% (58/141) and were all susceptible to macrolides while low-virulent strains characteristic of ptxP1/prn1/ptxC1 constituted 58.9% (83/141) and 97.6% (81/83), respectively, were highly resistant to macrolides.

CONCLUSIONS

Pertussis is resurging among infants and young children in Shanghai, and household transmission is the main exposure pathway. The high-virulent strains harboring ptxP3/prn2/ptxC2 and the macrolide-resistant Bordetella pertussis strains are quite prevalent. These issues impose a public health concern in Shanghai. Our findings are important to modify the DTaP vaccination strategy and the management guideline of pertussis in China.

Pertussis disease and transmission and host responses: insights from the baboon model of pertussis

Whooping cough is a highly contagious, acute respiratory disease, caused by the Gram-negative bacterium Bordetella pertussis (Bp). Despite the introduction and widespread use of vaccines starting in the 1950s pertussis cases continue to be reported, with a significant global impact. The role of specific virulence factors in disease and the immune mechanisms associated with protection following natural infection or vaccination are still not completely understood. The recently-developed baboon model of clinical pertussis provides a valuable tool for the study of pertussis. Baboons infected with B. pertussis exhibit all of the manifestations of human pertussis including paroxysmal coughing, mucus production, leukocytosis and transmission. The establishment of this model provides the opportunity to address unanswered questions about the natural progression of this disease and host responses to infection and vaccination in a very relevant model. In this review, we present an overview of our knowledge of pertussis along with recent advances resulting from use of the baboon model. Remaining questions and future research directions are discussed. We hope that the knowledge gained through use of the baboon model of pertussis and clinical studies will allow the development of more efficacious vaccines, conferring long lasting protection against disease and transmission.

Bordetella pertussis adenylate cyclase toxin: intoxication of host cells by bacterial invasion

Bordetella pertussis produces extracytoplasmic adenylate cyclase toxin (AC toxin) which penetrates target cells and, upon activation by host calmodulin, generates high levels of intracellular cyclic AMP (cAMP). As a result, bactericidal functions of immune effector cells are impaired. Since a considerable amount of AC toxin is associated with the bacterium, it was proposed that the toxin may be delivered by direct interaction of the organism with the target cells (E. L. Hewlett, M. C. Gray, and R. D. Pearson, Clin. Res. 35:477A, 1987). Incubation of CHO cells with intact B. pertussis led to formation of intracellular cAMP at levels comparable to those produced in CHO cells by equivalent activities of isolated AC toxin. cAMP accumulation induced by the whole bacteria appeared after a lag of 40 to 60 min and reached high levels within 2 to 3 h, whereas adherence of the bacteria proceeded rapidly and reached a maximal level within 80 min. Sera of pertussis patients completely blocked cAMP accumulation induced by the whole bacteria without having a major effect on either bacterial adherence or cAMP production by the AC toxin. Cytochalasins B and D, inhibitors of bacterial invasion, abrogated the cAMP response to the whole bacteria but not the response to the AC toxin. These agents did not affect bacterial adherence. Transmission electron micrographs revealed that B. pertussis, within the time course of cAMP induction, invaded CHO cells. We suggest that cAMP induction by B. pertussis is caused by the entry of the whole bacteria into CHO cells rather than by delivery of AC toxin during bacterial adherence. This route of cell intoxication may be relevant to the pathogenesis of whooping cough.

Association of Bordetella pertussis with host immune cells in the mouse lung

Mouse models are frequently used to study immunity and pathogenesis to Bordetella pertussis infection. To improve the understanding of the mouse infection model, the influx of host cells and B. pertussis localisation in the lungs were evaluated. Furthermore, the roles of filamentous hemagglutinin (FHA) and fimbriae (Fim) in these processes were determined. B. pertussis infection stimulated the recruitment of polymorphonuclear granulocytes (PMN), alveolar macrophages, and lymphocytes. As determined by double immunofluorescence staining, 2 hr after infection most B. pertussis were free in the alveolar space, some were attached to alveolar epithelia, and some were associated with and phagocytosed by PMN. After 3 days, most bacteria were associated with and phagocytosed by macrophages, some by PMN. B. pertussis was shown not to be ingested by epithelial cells or associated with interstitial macrophages. B. pertussis mutants lacking expression of FHA or Fim were associated with and phagocytosed by the same cell types as parental bacteria. The Fim mutant, however, induced a more severe inflammation, and was cleared faster from the lungs compared to the parental strain and the FHA mutant. These results suggest that Fim does not affect bacterial localisation in the mouse lung, but does influence host immune mechanisms. Possibly, Fim may exert an anti-inflammatory function and thereby inhibit killing by macrophages.

Prior Bordetella pertussis infection modulates allergen priming and the severity of airway pathology in a murine model of allergic asthma

BACKGROUND

It has been proposed that T helper (Th)2-driven immune deviation in early life can be countered by Th1 inducing childhood infections and that such counter-regulation can protect against allergic asthma.

OBJECTIVE

To test whether Th1-inducing infection with Bordetella pertussis protects against allergic asthma using well-characterized murine models.

METHODS

Groups of mice were sensitized to ovalbumin (OVA) in the presence or absence of B. pertussis, a well-characterized Th1 inducing respiratory infection. Immunological, pathological and physiological parameters were measured to assess the impact of infection on immune deviation and airway function.

RESULTS

We demonstrate that OVA sensitization does not affect the development of B. pertussis-specific immune responses dominated by IgG2a and IFN-gamma and does not impair Th1-mediated clearance of airway infection. In contrast, B. pertussis infection at the time of sensitization modulated the response to OVA and significantly reduced total serum and OVA-specific IgE. The pattern of cytokine responses, in particular OVA-specific IL-5 responses in the spleen was also modulated. However, B. pertussis did not cause global suppression as IL-10 and IL-13 levels were enhanced in OVA-stimulated spleen cell cultures and in lavage fluid from infected co-sensitized mice. Histopathological examination revealed that B. pertussis infection prior to OVA sensitization resulted in increased inflammation of bronchiolar walls with accompanying hyperplasia and mucous metaplasia of lining epithelia. These pathological changes were accompanied by increased bronchial hyper-reactivity to methacholine exposure.

CONCLUSION

Contrary to the above premise, a Th1 response induced by a common childhood infection does not protect against bronchial hyper-reactivity, but rather exacerbates the allergic asthmatic response, despite modulation of immune mediators.

Rapid diagnosis of pertussis in young infants: comparison of culture, PCR, and infant's and mother's serology

The contribution of maternal pertussis serology comparing prepartum serum to serum collected during the infant's disease to the diagnosis of pertussis in infants was evaluated for 28 pairs of young infants with pertussis syndrome and their mothers and was compared to those of culture and PCR. Infants had a nasopharyngeal aspiration tested by PCR, and acute and convalescent sera were collected during their disease. Mothers had a first acute serum collected concomitantly with the infant's acute serum, and both acute sera were compared to a prepartum serum. Sera were analyzed by immunoblotting for the detection of anti-pertussis toxin (PT) antibodies. Serological evidence of pertussis in infants was assessed as either an increase in anti-PT antibody levels between the mother's prepartum and acute sera or the presence of antibodies in the infant's acute serum and their absence in both the mother's acute and prepartum sera. Culture and PCR sensitivity were 43 and 89%, respectively. Most infants (18 of 24) had no pertussis antibody detectable in their acute sera, confirming a delayed immune response at this age. A comparison of infant's and mother's serology, using prepartum serum, rapidly confirmed the diagnosis in 57% of the cases. Although less sensitive than PCR, this serological method should be used for a rapid diagnosis of pertussis in young infants when culture and PCR are either not available or negative.

Correlation of Real Time PCR Cycle Threshold Cut-Off with Bordetella pertussis Clinical Severity

Bordetella pertussis testing performed using real-time polymerase chain reaction (RT-PCR) is interpreted based on a cycle threshold (Ct) value. At Public Health Ontario Laboratories (PHOL), a Ct value <36 is reported as positive, and Ct values ≥36 and <40 are reported as indeterminate. PHOL reported indeterminate results to physicians and public health units until May 2012, after which these results were only reported to physicians. We investigated the association between Ct value and disease symptom and severity to examine the significance of indeterminate results clinically, epidemiologically and for public health reporting. B. pertussis positive and indeterminate RT-PCR results were linked to pertussis cases reported in the provincial Integrated Public Health Information System (iPHIS), using deterministic linkage. Patients with positive RT-PCR results had a lower median age of 10.8 years compared to 12.0 years for patients with indeterminate results (p = 0.24). Hospitalized patients had significantly lower Ct values than non-hospitalized patients (median Ct values of 20.7 vs. 31.6, p<0.001). The proportion of patients reporting the most indicative symptoms of pertussis did not differ between patients with positive vs. indeterminate RT-PCR results. Taking the most indicative symptoms of pertussis as the gold-standard, the positive predictive value of the RT-PCR test was 68.1%. RT-PCR test results should be interpreted in the context of the clinical symptoms, age, vaccination status, prevalence, and other factors. Further information on interpretation of indeterminate RT-PCR results may be needed, and the utility of reporting to public health practitioners should be re-evaluated.

A marked decrease in L-selectin expression by leucocytes in infants with Bordetella pertussis infection: leucocytosis explained?

OBJECTIVE

Infants with Bordetella pertussis infection (whooping cough) have an unexplained lymphocytosis and leucocytosis characterized by an increase in small lymphocytes with convoluted and cleaved nuclei. To characterize these cells immunophenotyping using multiparameter flow cytometry was performed on leucocytes from a group of 11 infants aged 3-6 months with proven pertussis and from uninfected control subjects.

METHODOLOGY

The panel of monoclonal antibodies used to elucidate leucocyte subtypes included activation, adhesion, costimulatory, memory, T-helper (Th) 1 and Th2 markers.

RESULTS

Patients with pertussis showed an increase in absolute numbers of neutrophils, monocytes, T lymphocytes (both CD4 and CD8), B lymphocytes (including CD10+/CD19+ haematogones) and natural killer (NK) cells. All leucocyte subgroups showed a marked decrease in L-selectin (CD62L) expression. The expression of other adhesion molecules CD11a, CD44 and CD54 on all leucocyte subgroups was unchanged. Expression of costimulatory molecules, CD49D and CD28 on T cells and CD80 and CD86 on monocytes, was unchanged. Lymphocyte activation markers CD69, CD25 and HLA-DR were unchanged. There was an increase in CD45RA+/CD45RO+/CD4+ cells (activated) and CD62L-/CD45RO+/CD4+ cells (Th1-like) but no increase in CD7-/CD4+ T cells (Th2-like).

CONCLUSIONS

L-Selectin expression mediates extravasation of leucocytes into tissues and is important for homing of peripheral blood lymphocytes to lymph nodes. The significant down-regulation of L-selectin on leucocytes in pertussis infection may prevent leucocyte migration to areas of infection and homing and adhesion of T and B cells to peripheral lymphoid tissues. The increase in lymphocytes with Th1 phenotype may be required for effective immune response to the infective organism. These data provide a possible explanation for the absolute leucocytosis observed in this disease.

Marked increase in L-selectin-negative T cells in neonatal pertussis. The lymphocytosis explained?

The detailed immunophenotype of peripheral blood lymphocytes from a neonate with pertussis was determined by flow cytometry and compared with results from cord blood from healthy newborns. Most (72%) of the lymphocytes were CD3+ T cells with a normal CD4/CD8 ratio (2.5). The T cells were largely HLA-DR negative and CD45RA+, consistent with unstimulated naïve T cells. Almost all of the CD4+ T cells were Leu8 (L-selectin, CD62L) negative, while almost all of the CD8+ T cells were CD28+. There was no increase in CD7- CD4+ T cells (Th2-like). No relative increase in CD16/56+ NK cells (5%) or CD19/20+ B cells was seen. The most dramatic finding in this case was the remarkable lack of expression of L-selectin by the T cells. L-selectin expression is associated with homing of peripheral blood lymphocytes to lymph nodes. The dramatic reduction in L-selectin expression of the T lymphocytes in pertussis, perhaps induced by pertussis toxin, likely prevents homing of the T cells to peripheral lymphoid tissues and provides a likely explanation for the marked lymphocytosis noted in this disease.