Interferon-gamma levels in serum and bronchoalveolar lavage fluid of mice infected with Bordetella pertussis

Erythroid Suppressor Cells Compromise Neonatal Immune Response against Bordetella pertussis

Newborns are highly susceptible to infection. The underlying mechanism of neonatal infection susceptibility has generally been associated with neonatal immune cell immaturity. In this study, we challenged this notion and built upon our recent discovery that neonates are physiologically enriched with erythroid TER119⁺CD71⁺ cells (Elahi et al. 2013. Nature 504: 158-162). We have used Bordetella pertussis, a common neonatal respiratory tract infection, as a proof of concept to investigate the role of these cells in newborns. We found that CD71⁺ cells have distinctive immune-suppressive properties and suppress innate immune responses against B. pertussis infection. CD71⁺ cell ablation unleashed innate immune response and restored resistance to B. pertussis infection. In contrast, adoptive transfer of neonatal CD71⁺ cells into adult recipients impaired their innate immune response to B. pertussis infection. Enhanced innate immune response to B. pertussis was characterized by increased production of protective cytokines IFN-γ, TNF-α, and IL-12, as well as recruitment of NK cells, CD11b⁺, and CD11c⁺ cells in the lung. Neonatal and human cord blood CD71⁺ cells express arginase II, and this enzymatic activity inhibits phagocytosis of B. pertussis in vitro. Thus, our study challenges the notion that neonatal infection susceptibility is due to immune cell-intrinsic defects and instead highlights active immune suppression mediated by abundant CD71⁺ cells in the newborn. Our findings provide additional support for the novel theme in neonatal immunology that immunosuppression is essential to dampen robust immune responses in the neonate. We anticipate that our results will spark renewed investigation in modulating the function of these cells and developing novel strategies for enhancing host defense to infections in newborns.

c-di-GMP enhances protective innate immunity in a murine model of pertussis

Innate immunity represents the first line of defense against invading pathogens in the respiratory tract. Innate immune cells such as monocytes, macrophages, dendritic cells, NK cells, and granulocytes contain specific pathogen-recognition molecules which induce the production of cytokines and subsequently activate the adaptive immune response. c-di-GMP is a ubiquitous second messenger that stimulates innate immunity and regulates biofilm formation, motility and virulence in a diverse range of bacterial species with potent immunomodulatory properties. In the present study, c-di-GMP was used to enhance the innate immune response against pertussis, a respiratory infection mainly caused by Bordetella pertussis. Intranasal treatment with c-di-GMP resulted in the induction of robust innate immune responses to infection with B. pertussis characterized by enhanced recruitment of neutrophils, macrophages, natural killer cells and dendritic cells. The immune responses were associated with an earlier and more vigorous expression of Th1-type cytokines, as well as an increase in the induction of nitric oxide in the lungs of treated animals, resulting in significant reduction of bacterial numbers in the lungs of infected mice. These results demonstrate that c-di-GMP is a potent innate immune stimulatory molecule that can be used to enhance protection against bacterial respiratory infections. In addition, our data suggest that priming of the innate immune system by c-di-GMP could further skew the immune response towards a Th1 type phenotype during subsequent infection. Thus, our data suggest that c-di-GMP might be useful as an adjuvant for the next generation of acellular pertussis vaccine to mount a more protective Th1 phenotype immune response, and also in other systems where a Th1 type immune response is required.

The host defense peptide beta-defensin 1 confers protection against Bordetella pertussis in newborn piglets

Innate immunity plays an important role in protection against respiratory infections in humans and animals. Host defense peptides such as beta-defensins represent major components of innate immunity. We recently developed a novel porcine model of pertussis, an important respiratory disease of young children and infants worldwide. Here, we investigated the role of porcine beta-defensin 1 (pBD-1), a porcine defensin homologue of human beta-defensin 2, in conferring protection against respiratory infection with Bordetella pertussis. In this model, newborn piglets were fully susceptible to infection and developed severe bronchopneumonia. In contrast, piglets older than 4 weeks of age were protected against infection with B. pertussis. Protection was associated with the expression of pBD-1 in the upper respiratory tract. In fact, pBD-1 expression was developmentally regulated, and the absence of pBD-1 was thought to contribute to the increased susceptibility of newborn piglets to infection with B. pertussis. Bronchoalveolar lavage specimens collected from older animals as well as chemically synthesized pBD-1 displayed strong antimicrobial activity against B. pertussis in vitro. Furthermore, in vivo treatment of newborn piglets with only 500 mug pBD-1 at the time of challenge conferred protection against infection with B. pertussis. Interestingly, pBD-1 displayed no bactericidal activity in vitro against Bordetella bronchiseptica, a closely related natural pathogen of pigs. Our results demonstrate that host defense peptides play an important role in protection against pertussis and are essential in modulating innate immune responses against respiratory infections.

Immunity to Bordetella pertussis

Bordetella pertussis exploits extracellular and intracellular niches in the respiratory tract and a variety of immune evasion strategies to prolong its survival in the host. This article reviews evidence of complementary roles for cellular and humoral immunity in protection. It discusses the effector mechanisms of bacterial elimination, the strategies employed by the bacteria to subvert protective immune responses and the immunological basis for systemic and neurological responses to infection and vaccination.

Genetic analysis of the influence of pertussis toxin on experimental allergic encephalomyelitis susceptibility: an environmental agent can override genetic checkpoints

Pertussis toxin (PTX) is a potent ancillary adjuvant used to elicit several different autoimmune diseases, including experimental allergic encephalomyelitis (EAE). To delineate the genetics of PTX effect in EAE, we mapped EAE-modifying (eae-m) loci in cohorts of backcross mice immunized with and without PTX. In this study, we analyzed the genetic basis of EAE susceptibility and severity and the intermediate phenotypes of mononuclear cell infiltration, suppuration, and demyelination. In animals immunized with PTX, one major locus, eae9, controls disease susceptibility and severity. Eae9 also regulates the extent of mononuclear cell infiltration of the spinal cord in male mice. Without PTX, five eae-m loci were noted, including three new loci in intervals on chromosomes 8 (eae14), 10 (eae17), and 18 (eae18). Taken together, these results suggest that eae9 controls the effects of PTX in EAE susceptibility, and is capable of overriding the other genetic checkpoints in the pathogenesis of this disease.

Interferon-gamma mediated immune effector mechanisms against Bordetella pertussis

The role of IFN-gamma in reducing the intracellular load of Bordetella pertussis in murine macrophages in vitro has been examined. The results demonstrate that exposure to IFN-gamma can reduce bacterial load in viable macrophages and that this is associated with production of nitric oxide (NO). These observations provide a mechanism by which IFN-gamma may mediate its antimicrobial effect and support an important role for activated alveolar macrophages in the elimination of B. pertussis from the respiratory tract. Using intracellular iron chelation, it is shown that intracellular survival of B. pertussis is dependent on iron availability and suggest that iron restriction may be an important mechanism by which IFN-gamma influences bacterial survival within mouse macrophages. It is also shown that IFN-gamma may mediate its effect through NO independent mechanisms and that B. pertussis is sensitive to agents that stimulate the respiratory burst. Finally, it is shown that the concentration of L-tryptophan may be a limiting step in the intracellular survival of B. pertussis and that the induction of tryptophan degrading enzymes may be an additional mechanism through which IFN-gamma exerts its antimicrobial effects against B. pertussis.

Regulation of inflammatory responses to Bordetella pertussis by N(G)-monomethyl-L-arginine in mice intranasally infected

To investigate effect of MMLA, an inhibitor of nitric oxide (NO) production, on regulation of inflammatory responses to Bordetella pertussis infection, mice were infected intranasally, and treated with various concentrations of MMLA. Ten days after infection, mice treated with MMLA at dosage of 100 mg/kg, given intraperitoneally in a single dose or for 5 consecutive days, showed at histopathologic examination, a significant decrease of intensity of inflammation (scores, 0.6 +/- 0.2 and 0.9 +/- 0.5 respectively). A decrease of cellular accumulation of neutrophils and lymphocytes in the bronchoalveolar lavage (BAL) fluid was observed in infected mice treated with MMLA, especially at dosage of 10 mg/kg, given in a single dose intraperitoneally. In addition, BP-infected mice treated with MMLA (100 mg/kg, intraperitoneally) for 5 consecutive days showed higher mortality rate than untreated mice infected with B. pertussis, and the number of B. pertussis in lungs of mice treated with MMLA was significantly increased. However, MMLA treatment of infected mice had some effect on levels of IFN-gamma and nitrite/nitrate (end-stable products of NO) in the BAL fluid. This study indicates that NO may play a role either as microbiocidal agent or as a modulator of immune regulation, inasmuch as it may upregulate tissue inflammatory response to B. pertussis.

Pertussis toxin enhanced IgG1 and IgE responses to primary tetanus immunization are mediated by interleukin-4 and persist during secondary responses to tetanus alone

Pertussis toxin (Ptx), the major toxin product of Bordetella pertussis, has potent immunologic effect including adjuvant effects on antibody responses and sensitization for anaphylaxis. In order to further define the effect of Ptx on the class and subclass of murine antibody response, we measured total and antigen specific IgG subclasses and IgE in Balb/c mice after primary and secondary immunization with tetanus toxoid (TT). Low doses of Ptx (100 ng) given intravenously at the time of primary immunization increased primary IgG1 and IgE anti-TT antibodies as well as total IgG1 and IgE concentrations compared to controls. The increase in IgG1 subclass and IgE response when Ptx was present during primary immunization was even more pronounced after secondary immunization with TT alone 3 weeks or 3 months later. Similar effects were noted after diphtheria toxoid immunization in the presence of Ptx. Administration of the anti IL-4 monoclonal antibody (11B11) suppressed the enhanced total and TT-specific IgE responses but not the enhanced IgG1 responses. The presence of low concentrations of Ptx during primary immunization primes for induction of IL-4 producing T-cell help which enhances IgGI and IgE responses to the primary exposure as well as to subsequent exposures of the antigen in the absence of Ptx. This phenomenon may have significance for the adjuvant activity of vaccines containing Ptx as well as for the immune response to natural pertussis.

Effects of recombinant human gamma interferon on intracellular survival of Bordetella pertussis in human phagocytic cells

Several studies have demonstrated that Bordetella pertussis has the ability to enter and survive intracellularly within human polymorphonuclear leukocytes (PMNL) and human monocytes/macrophages. The effects of human recombinant gamma interferon (IFN-gamma) on the survival of B. pertussis in PMNL and human monocytes, and on the oxidative burst activity of PMNL and human monocytes in response to B. pertussis were assessed in this study. IFN-gamma partially increased intracellular killing of phagocytosed B. pertussis in human monocytes, as determined by an orange acridine-crystal violet assay. In contrast, IFN-gamma did not enhance intracellular killing of B. pertussis in PMNL. No significant increase of superoxide production was noted in human monocytes in response to B. pertussis when stimulated with various concentrations of IFN-gamma. The partial increase of B. pertussis killing by IFN-gamma within monocytes, together with poor production of superoxide may explain how B. pertussis can survive within human phagocytic cells, and thus cause a more prolonged course of the disease.

Toxicity of staphylococcal enterotoxins potentiated by lipopolysaccharide: major histocompatibility complex class II molecule dependency and cytokine release

The biological effects of staphylococcal enterotoxins (SE), potentiated by bacterial lipopolysaccharide (LPS), were studied with mice. Control animals survived the maximum dose of either SE or LPS, while mice receiving both agents died. SEA was 43-fold more potent than SEB and 20-fold more potent than SEC1. The mechanism of toxicity was further examined with transgenic mice deficient in major histocompatibility complex class I or II expression. Class II-deficient mice were resistant to SEA or SEB. However, class I-deficient animals were less susceptible to SEA (30% lethality) than wild-type mice (93% lethality). In vitro stimulation of T cells from the three mouse phenotypes by SEA correlated well with toxicity. T cells from transgenic or wild-type mice were similarly responsive to SEA when presented by irradiated, wild-type mononuclear cells. These data confirmed that the toxicity of SE was mainly exerted through a mechanism dependent on the expression of major histocompatibility complex class II molecules. Toxicity was also linked to stimulated cytokine release. Levels in serum of tumor necrosis factor alpha, interleukin-6, and gamma interferon peaked 2 to 4 h after the potentiating dose of LPS but returned to normal within 10 h. Concentrations of interleukin-1 alpha were also maximal after 2 h but remained above the background for up to 22 h. Relative to the levels in mice given only SEA or LPS, the levels in serum of tumor necrosis factor alpha, interleukin-6, and gamma interferon increased 5-, 10-, and 15-fold, respectively, after injections of SEA plus LPS. There was only an additive effect of SEA and LPS on interleukin-1 alpha concentrations.