Antibodies specific for the high-molecular-weight adhesion proteins of nontypeable Haemophilus influenzae are opsonophagocytic for both homologous and heterologous strains

Phase variable acetylation of lipooligosaccharide modifies antibody production and opsonophagocytic killing of non-typeable Haemophilus influenzae

Non-typeable Haemophilus influenzae (NTHi) causes millions of infections each year. Though it is primarily known to cause otitis media, recent studies have shown NTHi is emerging as a primary pathogen for invasive infection, prompting the need for new vaccines and treatments. Lipooligosaccharide (LOS) has been identified as a potential vaccine candidate due to its immunogenic nature and outer membrane localization. Yet, phase variable expression of genes involved in LOS synthesis has complicated vaccine development. In this study, we used a chinchilla model of otitis media to investigate how phase variation of oafA, a gene involved in LOS biosynthesis, affects antibody production in response to infection. We found that acetylation of LOS by OafA inhibited production of LOS-specific antibodies during infection and that NTHi expressing acetylated LOS were subsequently better protected against opsonophagocytic killing. These findings highlight the importance of understanding how phase variable modifications might affect vaccine efficacy and success.

The Lst Sialyltransferase of Neisseria gonorrhoeae Can Transfer Keto-Deoxyoctanoate as the Terminal Sugar of Lipooligosaccharide: a Glyco-Achilles Heel That Provides a New Strategy for Vaccines to Prevent Gonorrhea

The lipooligosaccharide (LOS) of Neisseria gonorrhoeae plays key roles in pathogenesis and is composed of multiple possible glycoforms. These glycoforms are generated by the process of phase variation and by differences in the glycosyltransferase gene content of particular strains. LOS glycoforms of N. gonorrhoeae can be terminated with an N-acetylneuraminic acid (Neu5Ac), which imparts resistance to the bactericidal activity of serum. However, N. gonorrhoeae cannot synthesize the CMP-Neu5Ac required for LOS biosynthesis and must acquire it from the host. In contrast, Neisseria meningitidis can synthesize endogenous CMP-Neu5Ac, the donor molecule for Neu5Ac, which is a component of some meningococcal capsule structures. Both species have an almost identical LOS sialyltransferase, Lst, that transfers Neu5Ac from CMP-Neu5Ac to the terminus of LOS. Lst is homologous to the LsgB sialyltransferase of nontypeable Haemophilus influenzae (NTHi). Studies in NTHi have demonstrated that LsgB can transfer keto-deoxyoctanoate (KDO) from CMP-KDO to the terminus of LOS in place of Neu5Ac. Here, we show that Lst can also transfer KDO to LOS in place of Neu5Ac in both N. gonorrhoeae and N. meningitidis Consistent with access to the pool of CMP-KDO in the cytoplasm, we present data indicating that Lst is localized in the cytoplasm. Lst has previously been reported to be localized on the outer membrane. We also demonstrate that KDO is expressed as a terminal LOS structure in vivo in samples from infected women and further show that the anti-KDO monoclonal antibody 6E4 can mediate opsonophagocytic killing of N. gonorrhoeae Taken together, these studies indicate that KDO expressed on gonococcal LOS represents a new antigen for the development of vaccines against gonorrhea.IMPORTANCE The emergence of multidrug-resistant N. gonorrhoeae strains that are resistant to available antimicrobials is a current health emergency, and no vaccine is available to prevent gonococcal infection. Lipooligosaccharide (LOS) is one of the major virulence factors of N. gonorrhoeae The sialic acid N-acetylneuraminic acid (Neu5Ac) is present as the terminal glycan on LOS in N. gonorrhoeae In this study, we made an unexpected discovery that KDO can be incorporated as the terminal glycan on LOS of N. gonorrhoeae by the alpha-2,3-sialyltransferase Lst. We showed that N. gonorrhoeae express KDO on LOS in vivo and that the KDO-specific monoclonal antibody 6E4 can direct opsonophagocytic killing of N. gonorrhoeae These data support further development of KDO-LOS structures as vaccine antigens for the prevention of infection by N. gonorrhoeae.

Phase-variable bacterial loci: how bacteria gamble to maximise fitness in changing environments

Phase-variation of genes is defined as the rapid and reversible switching of expression - either ON-OFF switching or the expression of multiple allelic variants. Switching of expression can be achieved by a number of different mechanisms. Phase-variable genes typically encode bacterial surface structures, such as adhesins, pili, and lipooligosaccharide, and provide an extra contingency strategy in small-genome pathogens that may lack the plethora of 'sense-and-respond' gene regulation systems found in other organisms. Many bacterial pathogens also encode phase-variable DNA methyltransferases that control the expression of multiple genes in systems called phasevarions (phase-variable regulons). The presence of phase-variable genes allows a population of bacteria to generate a number of phenotypic variants, some of which may be better suited to either colonising certain host niches, surviving a particular environmental condition and/or evading an immune response. The presence of phase-variable genes complicates the determination of an organism's stably expressed antigenic repertoire; many phase-variable genes are highly immunogenic, and so would be ideal vaccine candidates, but unstable expression due to phase-variation may allow vaccine escape. This review will summarise our current understanding of phase-variable genes that switch expression by a variety of mechanisms, and describe their role in disease and pathobiology.

Cytoplasmic glycoengineering of Apx toxin fragments in the development of Actinobacillus pleuropneumoniae glycoconjugate vaccines

BACKGROUND

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia and represents a major burden to the livestock industry. Virulence can largely be attributed to the secretion of a series of haemolytic toxins, which are highly immunogenic. A. pleuropneumoniae also encodes a cytoplasmic N-glycosylation system, which involves the modification of high molecular weight adhesins with glucose residues. Central to this process is the soluble N-glycosyl transferase, ngt, which is encoded in an operon with a subsequent glycosyl transferase, agt. Plasmid-borne recombinant expression of these genes in E. coli results in the production of a glucose polymer on peptides containing the appropriate acceptor sequon, NX(S/T). However to date, there is little evidence to suggest that such a glucose polymer is formed on its target peptides in A. pleuropneumoniae. Both the toxins and glycosylation system represent potential targets for the basis of a vaccine against A. pleuropneumoniae infection.

RESULTS

In this study, we developed cytoplasmic glycoengineering to construct glycoconjugate vaccine candidates composed of soluble toxin fragments modified by glucose. We transferred ngt and agt to the chromosome of Escherichia coli in order to generate a native-like operon for glycoengineering. A single chromosomal copy of ngt and agt resulted in the glucosylation of toxin fragments by a short glycan, rather than a polymer.

CONCLUSIONS

A vaccine candidate that combines toxin fragment with a conserved glycan offers a novel approach to generating epitopes important for both colonisation and disease progression.

The HMW2 adhesin of non-typeable Haemophilus influenzae is a human-adapted lectin that mediates high-affinity binding to 2-6 linked N-acetylneuraminic acid glycans

Non-typeable Haemophilus influenzae (NTHi) is a human-adapted bacterial pathogen, responsible for infections of the human respiratory tract. This pathogen expresses a range of adhesins that mediate binding to host cells. Most NTHi strains can express the related adhesins HMW1 and HMW2. Expression of HMW proteins is phase-variable: changes in the length of simple-sequence repeats located in the encoding genes promoter regions results in changes in expression levels of these adhesins. HMW expression is also controlled by epigenetic regulation. HMW1 has been previously demonstrated to bind α 2-3 sialyl-lactosamine, but affinity of this interaction has not been investigated. The host receptor(s) for HMW2 is currently unknown. We hypothesized that host glycans may act as receptors for HMW2-mediated adherence. We examined the glycan-binding activity of HMW2 using glycan arrays and Surface Plasmon Resonance (SPR). These studies demonstrate that HMW2 binds 2-6 linked N-acetylneuraminic acid with high affinity. HMW2 did not bind glycan structures containing the non-human form of sialic acid, N-glycolylneuraminic acid. Thus, the specificity of HMW1 and HMW2 have complementary lectin activities that may allow NTHi distinct niches in the human host.

Recognition of conserved antigens by Th17 cells provides broad protection against pulmonary Haemophilus influenzae infection

Nontypeable Haemophilus influenzae (NTHi) is a major cause of community acquired pneumonia and exacerbation of chronic obstructive pulmonary disease. A current effort in NTHi vaccine development has focused on generating humoral responses and has been greatly impeded by antigenic variation among the numerous circulating NTHi strains. In this study, we showed that pulmonary immunization of mice with killed NTHi generated broad protection against lung infection by different strains. While passive transfer of immune antibodies protected only against the homologous strain, transfer of immune T cells conferred protection against both homologous and heterologous strains. Further characterization revealed a strong Th17 response that was cross-reactive with different NTHi strains. Responding Th17 cells recognized both cytosolic and membrane-associated antigens, while immune antibodies preferentially responded to surface antigens and were highly strain specific. We further identified several conserved proteins recognized by lung Th17 cells during NTHi infection. Two proteins yielding the strongest responses were tested as vaccine candidates by immunization of mice with purified proteins plus an adjuvant. Immunization induced antigen-specific Th17 cells that recognized different strains and, upon adoptive transfer, conferred protection. Furthermore, immunized mice were protected against challenge with not only NTHi strains but also a fully virulent, encapsulated strain. Together, these results show that the immune mechanism of cross-protection against pneumonia involves Th17 cells, which respond to a broad spectrum of antigens, including those that are highly conserved among NTHi strains. These mechanistic insights suggest that inclusion of Th17 antigens in subunit vaccines offers the advantage of inducing broad protection and complements the current antibody-based approaches.

Immunogenicity of Nontypeable Haemophilus influenzae Outer Membrane Vesicles and Protective Ability in the Chinchilla Model of Otitis Media

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria are enriched in several outer membrane components, including major and minor outer membrane proteins and lipooligosaccharide. We assessed the functional activity of nontypeable Haemophilus influenzae (NTHi) OMV-specific antisera and the protective ability of NTHi OMVs as vaccine antigens in the chinchilla otitis media model. OMVs were purified from three HMW1/HMW2-expressing NTHi strains, two of which were also engineered to overexpress Hia proteins. OMV-specific antisera raised in guinea pigs were assessed for their ability to mediate killing of representative NTHi in an opsonophagocytic assay. The three OMV-specific antisera mediated killing of 18 of 65, 24 of 65, and 30 of 65 unrelated HMW1/HMW2-expressing NTHi strains. Overall, they mediated killing of 39 of 65 HMW1/HMW2-expressing strains. The two Hia-expressing OMV-specific antisera mediated killing of 17 of 25 and 14 of 25 unrelated Hia-expressing NTHi strains. Overall, they mediated killing of 20 of 25 Hia-expressing strains. OMVs from prototype NTHi strain 12 were used to immunize chinchillas and the course of middle ear infection was monitored following intrabullar challenge with the homologous strain. All control animals developed culture-positive otitis media, as did two of three HMW1/HMW2-immunized animals. All OMV-immunized animals, with or without supplemental HMW1/HMW2 immunization, were completely protected against otitis media. NTHi OMVs are the first immunogens examined in this model that provided complete protection with sterile immunity after NTHi strain 12 challenge. These data suggest that NTHi OMVs hold significant potential as components of protective NTHi vaccines, possibly in combination with HMW1/HMW2 proteins.

Recombinant truncated E protein as a new vaccine candidate against nontypeable H. influenzae: Its expression and immunogenic evaluation

Protein E (PE) is a conserved entity observed in both nontypeable Haemophilus influenzae (NTHi) and encapsulated H. influenzae. This is a small surface lipoprotein, consisting of only 160 amino acids, involved in the adhesion of H. influenzae to various types of epithelial cells. A 384-bp-long fragment from NTHi PE was cloned into the prokaryotic expression vector pBAD-gIIIA. The recombinant protein was expressed with arabinose and then purified by affinity purification on an Ni-NTA agarose matrix. BALB/c mice were immunized by subcutaneous injection with purified recombinant truncated PE mixed with an alum adjuvant. Serum antibody response and the functional activity of antibodies were evaluated by enzyme-linked immunosorbent assay (ELISA) and serum bactericidal assay (SBA), respectively. Colony PCR, double digestion, and sequencing were used to verify successful cloning of truncated PE. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analyses indicated the presence of a ∼15-kDa recombinant protein. Serum IgG, IgG1, and IgG2a levels were significantly higher in the group immunized by recombinant truncated PE mixed with an alum adjuvant, compared to the non-vaccinated control group. Development of a strong bactericidal effect against NTHi was observed in the serum samples from immunized animals. Our findings suggest that recombinant truncated PE is a potential vaccine candidate for NTHi.

Recombinant C-terminal 311 amino acids of HapS adhesin as a vaccine candidate for nontypeable Haemophilus influenzae: A study on immunoreactivity in Balb/C mouse

Hap, an auto-transporter protein, is an antigenically conserved adhesion protein which is present on both typeable and nontypeable Haemophilus influenzae. This protein has central role in bacterial attachment to respiratory tract epithelial cells. A 1000bp C-terminal fragment of Hap passenger domain (HapS) from nontypeable Haemophilus influenzae was cloned into a prokaryotic expression vector, pET-24a. BALB/c mice were immunized subcutaneously with purified rC-HapS. Serum IgG responses to purified rC-HapS, serum IgG subclasses were determined by ELISA and functional activity of antibodies was examined by Serum Bactericidal Assay. The output of rC-HapS was approximately 62% of the total bacterial proteins. Serum IgG responses were significantly increased in immunized group with rC-HapS mixed with Freund's adjuvant in comparison with control groups. Analysis of the serum IgG subclasses showed that the IgG1 subclass was predominant after subcutaneous immunization in BALB/c mice (IgG2a/IgG1 < 1). The sera from rC-HapS immunized animals were strongly bactericidal against nontypeable Haemophilus influenzae. These results suggest that rC-HapS may be a potential vaccine candidate for nontypeable Haemophilus influenzae.

Developing a vaccine to prevent otitis media caused by nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is a predominant organism of the upper respiratory nasopharyngeal microbiota. Its disease spectrum includes otitis media, sinusitis, non-bacteremic pneumonia and invasive infections. Protein-based vaccines to prevent NTHi infections are needed to alleviate these infections in children and vulnerable populations such as the elderly and those with chronic obstructive pulmonary disease (COPD). One NTHi protein is included in a pneumococcal conjugate vaccine and has been shown to provide efficacy. Our lab has been interested in understanding the immunogenicity of NTHi vaccine candidates P6, protein D and OMP26 for preventing acute otitis media in young children. We expect that continued investigation and progress in the development of an efficacious protein based vaccine against NTHi infections is achievable in the near future.

Naturally Acquired HMW1- and HMW2-Specific Serum Antibodies in Adults and Children Mediate Opsonophagocytic Killing of Nontypeable Haemophilus influenzae

The HMW1 and HMW2 proteins are highly immunogenic adhesins expressed by approximately 75% of nontypeable Haemophilus influenzae (NTHi) strains, and HMW1- and HMW2-specific antibodies can mediate opsonophagocytic killing of NTHi. In this study, we assessed the ability of HMW1- and HMW2-specific antibodies in sera from healthy adults and convalescent-phase sera from children with NTHi otitis media to mediate killing of homologous and heterologous NTHi. The serum samples were examined pre- and postadsorption on HMW1 and HMW2 affinity columns, and affinity-purified antibodies were assessed for ability to mediate killing of homologous and heterologous strains. Adult serum samples mediated the killing of six prototype NTHi strains at titers of <1:10 to 1:1,280. HMW1- and HMW2-adsorbed sera demonstrated unchanged to 8-fold decreased opsonophagocytic titers against the homologous strains. Each affinity-purified antibody preparation mediated the killing of the respective homologous strain at titers of <1:10 to 1:320 and of the five heterologous strains at titers of <1:10 to 1:320, with most preparations killing most heterologous strains to some degree. None of the acute-phase serum samples from children mediated killing, but each convalescent-phase serum sample mediated killing of the infecting strain at titers of 1:40 to 1:640. HMW1- and HMW2-adsorbed convalescent-phase serum samples demonstrated ≥4-fold decreases in titer. Three of four affinity-purified antibody preparations mediated killing of the infecting strain at titers of 1:20 to 1:320, but no killing of representative heterologous strains was observed. HMW1- and HMW2-specific antibodies capable of mediating opsonophagocytic killing are present in the serum from normal adults and develop in convalescent-phase sera of children with NTHi otitis media. Continued investigation of the HMW1 and HMW2 proteins as potential vaccine candidates for the prevention of NTHi disease is warranted.

A biphasic epigenetic switch controls immunoevasion, virulence and niche adaptation in non-typeable Haemophilus influenzae

Non-typeable Haemophilus influenzae contains an N⁶-adenine DNA-methyltransferase (ModA) that is subject to phase-variable expression (random ON/OFF switching). Five modA alleles, modA2, modA4, modA5, modA9 and modA10, account for over two-thirds of clinical otitis media isolates surveyed. Here, we use single molecule, real-time (SMRT) methylome analysis to identify the DNA-recognition motifs for all five of these modA alleles. Phase variation of these alleles regulates multiple proteins including vaccine candidates, and key virulence phenotypes such as antibiotic resistance (modA2, modA5, modA10), biofilm formation (modA2) and immunoevasion (modA4). Analyses of a modA2 strain in the chinchilla model of otitis media show a clear selection for ON switching of modA2 in the middle ear. Our results indicate that a biphasic epigenetic switch can control bacterial virulence, immunoevasion and niche adaptation in an animal model system.

Non-typeable Haemophilus influenzae, which causes ear and lung infections, has a DNA methyltransferase encoded by alternative alleles that are subject to random ON/OFF switching. Here, Atack et al. show that this epigenetic switch controls the expression of key proteins involved in virulence.

Vaccines for Nontypeable Haemophilus influenzae: the Future Is Now

Infections due to nontypeable Haemophilus influenzae result in enormous global morbidity in two clinical settings: otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). Recurrent otitis media affects up to 20% of children and results in hearing loss, delays in speech and language development and, in developing countries, chronic suppurative otitis media. Infections in people with COPD result in clinic and emergency room visits, hospital admissions, and respiratory failure. An effective vaccine would prevent morbidity, help control health care costs, and reduce antibiotic use, a major contributor to the global crisis in bacterial antibiotic resistance. The widespread use of the pneumococcal conjugate vaccines is causing a relative increase in H. influenzae otitis media. The partial protection against H. influenzae otitis media induced by the pneumococcal H. influenzae protein D conjugate vaccine represents a proof of principle of the feasibility of a vaccine for nontypeable H. influenzae. An ideal vaccine antigen should be conserved among strains, have abundant epitopes on the bacterial surface, be immunogenic, and induce protective immune responses. Several surface proteins of H. influenzae have been identified as potential vaccine candidates and are in various stages of development. With continued research, progress toward a broadly effective vaccine to prevent infections caused by nontypeable H. influenzae is expected over the next several years.

Evaluation and validation of a serum bactericidal antibody assay for Haemophilus influenzae type b and the threshold of protection

Prior to routine immunisation, Haemophilus influenzae serotype b (Hib) was a major cause of serious bacterial infections, particularly in young children. In the United Kingdom, introduction of the Hib conjugate vaccine into the national childhood immunisation schedule has led to a sustained decline in invasive Hib disease across all age-groups. Evaluation of the immune response to Hib conjugate vaccines involves measurement of serum IgG antibodies against the capsular polyribosyl-ribitol-phosphate (PRP) polysaccharide by enzyme-linked immunosorbent assay (ELISA), with accepted short-term and long-term protective thresholds of ≥0.15μg/mL and ≥1.0μg/mL, respectively. These levels were derived by passive immunisation or immunisation with pure polysaccharide, and their relevance for protection following immunisation with conjugate vaccines remains unclear. This study aimed to modify and optimise a serum bactericidal antibody (SBA) assay to evaluate the functional activity of Hib antibodies generated following Hib conjugate vaccination. Validation of the Hib SBA assay was deemed acceptable for all assay parameters tested. A strong correlation between anti-PRP IgG concentrations and SBA titres was observed in vaccinated adults (r=0.81), as well as infants after primary immunisation at 2, 3, and 4 months (r=0.635) and after the 12-month booster (r=0.746). The assay identified some children with high anti-PRP IgG but low SBA activity and vice versa. The predictive protective SBA titre corresponding to a post-booster anti-PRP IgG of 1.0μg/mL was 8. Thus, the optimised Hib SBA assay was specific and reproducible and correlated with anti-PRP IgG. Such assays may have a role in evaluating immune responses to conjugate vaccines in addition to measuring capsular antibodies.

Antibodies to the HMW1/HMW2 and Hia adhesins of nontypeable haemophilus influenzae mediate broad-based opsonophagocytic killing of homologous and heterologous strains

The HMW1/HMW2 and Hia proteins are highly immunogenic surface adhesins of nontypeable Haemophilus influenzae (NTHi). Approximately 75% of NTHi strains express HMW1/HMW2 adhesins, and most of the remaining 25% express an Hia adhesin. Our objective in this study was to assess the ability of antisera raised against purified HMW1/HMW2 proteins or recombinant Hia proteins to mediate opsonophagocytic killing of a large panel of unrelated NTHi strains. Native HMW1/HMW2 proteins were purified from three HMW1/HMW2-expressing NTHi strains. Recombinant fusion proteins expressing surface-exposed segments of either of two prototype Hia proteins were purified from Escherichia coli transformants. Immune sera raised in guinea pigs were assessed for their ability to mediate killing of NTHi in an opsonophagocytic assay with the HL-60 phagocytic cell line. The three HMW1/HMW2 antisera mediated killing of 22 of 65, 43 of 65, and 28 of 65 unrelated HMW1/HMW2-expressing NTHi strains, respectively. As a group, the three sera mediated killing of 48 of 65 HMW1/HMW2-expressing strains. The two Hia immune sera mediated killing of 12 of 24 and 13 of 24 unrelated Hia-expressing NTHi strains, respectively. Together, they mediated killing of 15 of 24 Hia-expressing strains. Neither the HMW1/HMW2 nor the Hia antisera mediated killing of NTHi expressing the alternative adhesin type. Antibodies directed against native HMW1/HMW2 proteins and recombinant Hia proteins are capable of mediating broad-based opsonophagocytic killing of homologous and heterologous NTHi strains. A vaccine formulated with a limited number of HMW1/HMW2 and Hia proteins might provide protection against disease caused by most NTHi strains.

Absence of high molecular weight proteins 1 and/or 2 is associated with decreased adherence among non-typeable Haemophilus influenzae clinical isolates

High molecular weight (Hmw) proteins 1 and 2, type IV pilin protein (PilA), outer-membrane protein P5 (OmpP5), Haemophilus protein D (Hpd) and Haemophilus adhesive protein (Hap) are surface proteins involved in the adherence of non-typeable Haemophilus influenzae. One hundred clinical isolates were evaluated for the presence of the genes encoding these proteins by PCR and for their adherence capacity (AC) to Detroit 562 nasopharyngeal cells (D562). The majority of isolates were from blood (77/100); other sites were also represented. Confluent D562 monolayers (1.2×105 cells per well) were inoculated with standardized minimal infective doses (m.o.i.) of 102, 103 or 104 c.f.u. per well. The AC was categorized as low (<10 %) or high (≥10 %) depending on the percentage of c.f.u. adhering per well. All the isolates evaluated showed adherence: 69/100 (69 %) demonstrated high adherence, while 31/100 (31 %) showed low adherence. Of all the genes evaluated, hmw1A and/or hmw2A were detected in 69/100 (69 %) of isolates. The presence of hmw1A and/or hmw2A was associated with increased adherence to D562 cells (P≤0.001). Dot immunoblots were performed to detect protein expression using mAbs 3D6, AD6 and 10C5. Among the high-adherence isolates (n = 69), 72 % reacted with 3D6 and 21 % with 10C5. Our data indicate that the absence of Hmw1 and/or Hmw2 was associated with decreased adherence to D562 cells.

Protective effect of IgM against colonization of the respiratory tract by nontypeable Haemophilus influenzae in patients with hypogammaglobulinemia

BACKGROUND

Primary immunoglobulin deficiencies lead to recurrent bacterial infections of the respiratory tract and bronchiectasis, even with adequate immunoglobulin replacement therapy. It is not known whether patients able to secrete IgM (eg, those with hyper-IgM [HIgM] syndrome) are as susceptible to these infections as patients who lack IgM production (eg, those with panhypogammaglobulinemia [PHG]).

OBJECTIVE

This study is aimed at identifying specific microbiological and clinical (infections) characteristics that distinguish immunoglobulin-substituted patients with PHG from patients with HIgM syndrome.

METHODS

A cohort of patients with HIgM syndrome (n = 25) and a cohort of patients with PHG (n = 86) were monitored prospectively for 2 years while receiving similar polyvalent immunoglobulin replacement therapies. Regular bacterial analyses of nasal swabs and sputum were performed, and clinical events were recorded. In parallel, serum and saliva IgM antibody concentrations were measured.

RESULTS

When compared with patients with PHG, patients with HIgM syndrome were found to have a significantly lower risk of nontypeable Haemophilus influenzae carriage in particular (relative risk, 0.39; 95% CI, 0.21-0.63). Moreover, patients with HIgM syndrome (including those unable to generate somatic hypermutations of immunoglobulin genes) displayed anti-nontypeable H influenzae IgM antibodies in their serum and saliva. Also, patients with HIgM syndrome had a lower incidence of acute respiratory tract infections.

CONCLUSIONS

IgM antibodies appear to be microbiologically and clinically protective and might thus attenuate the infectious consequences of a lack of production of other immunoglobulin isotypes in patients with HIgM syndrome. Polyvalent IgG replacement therapy might not fully compensate for IgM deficiency. It might thus be worth adapting long-term antimicrobial prophylactic regimens according to the underlying B-cell immunodeficiency phenotype.

Construction and immunogenicity of recombinant adenovirus vaccines expressing the HMW1, HMW2, or Hia adhesion protein of nontypeable Haemophilus influenzae

The objective of the present study was to construct and assess the immunogenicity of recombinant adenovirus vectors expressing the HMW1, HMW2, or Hia protein of nontypeable Haemophilus influenzae (NTHi). These proteins are critical adhesins and potential protective antigens expressed by NTHi. Segments of the hmw1A and hmw2A structural genes that encode the distal one-half of mature HMW1 or HMW2 were cloned into the T7 expression vector pGEMEX-2. These constructs encoded stable HMW1 or HMW2 recombinant fusion protein that expresses B-cell epitopes common to most NTHi strains. A segment of the hia gene that encodes the surface-exposed portion of mature Hia was also cloned into pGEMEX-2. The resulting T7 gene 10 translational fusions were excised from the parent plasmids and cloned into the shuttle plasmid pDC316. Cotransfection of HEK 293 cells with the pDC316 derivatives and pBHGloxΔE1,3Cre resulted in the production of viral plaques from which recombinant adenoviruses expressing fusion proteins were recovered. Chinchillas immunized intraperitoneally with a single 10(8)-PFU dose of either the HMW2 or Hia adenoviral construct developed high anti-HMW2 or anti-Hia serum antibody titers within 4 weeks of immunization. Chinchillas immunized intranasally with a single 10(7)- to 10(9)-PFU dose of the Hia adenoviral construct also developed high anti-Hia serum antibody titers within 8 weeks of immunization. Recombinant adenoviruses represent a promising system to induce mucosal and systemic immunity and protection against mucosal diseases such as otitis media. Recombinant adenoviruses expressing recombinant HMW1, HMW2, or Hia protein will be important new tools in NTHi vaccine development efforts.

Current and Future Prospects for a Vaccine for Nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae is an important human respiratory tract pathogen that causes about 30% of otitis media in infants and children. This proportion is increasing as a result of pneumococcal conjugate vaccines. Because of the morbidity associated with otitis media, a strong rationale exists to develop strategies to prevent these infections. A challenge to developing a vaccine for nontypeable H. influenzae is the antigenic heterogeneity of several major surface antigens and the genetic heterogeneity among strains. Several research groups have identified conserved surface proteins and tested them as putative vaccines. A recent clinical trial with protein D, a conserved surface antigen, demonstrated partial efficacy in preventing H. influenzae otitis media. This important result provides a proof of principle for developing a vaccine to prevent otitis media caused by nontypeable H. influenzae. Several vaccine antigens for nontypeable H. influenzae are in development.

Antibodies specific for the Hia adhesion proteins of nontypeable Haemophilus influenzae mediate opsonophagocytic activity

The Hia autotransporter proteins are highly immunogenic surface adhesins expressed by nontypeable Haemophilus influenzae (NTHI). The objective of our study was to assess the opsonophagocytic activity of anti-Hia antibodies against homologous and heterologous NTHI. A segment of the hia gene that encodes a surface-exposed portion of the H. influenzae strain 11 Hia protein was cloned into a pGEMEX-2 expression vector. Escherichia coli JM101 was transformed with the resulting pGEMEX-Hia BstEII del recombinant plasmid, and recombinant fusion protein was recovered. An immune serum against recombinant GEMEX-Hia (rGEMEX-Hia)-mediated killing of the homologous NTHI strain 11 at a 1:160 titer and five heterologous Hia-expressing strains at titers of > or =1:40. Immune serum did not mediate killing of two Hia-knockout strains whose hia genes were inactivated but did mediate killing of one knockout strain at a high titer after the strain was transformed with a plasmid containing the hia gene. Immune serum did not mediate killing of HMW1/HMW2-expressing NTHI strains, which do not express the Hia adhesin. However, when two representative HMW1/HMW2-expressing strains were transformed with the plasmid containing the hia gene, they expressed abundant Hia and were susceptible to killing by the immune serum. Immune serum did not mediate killing of HMW1/HMW2-expressing strains transformed with the plasmid without the hia gene. Our results demonstrate that the Hia proteins of NTHI are targets of opsonophagocytic antibodies and that shared epitopes recognized by such antibodies are present on the Hia proteins of unrelated NTHI strains. These data argue for the continued investigation of the Hia proteins as vaccine candidates for the prevention of NTHI disease.

Resistance of Haemophilus influenzae to reactive nitrogen donors and gamma interferon-stimulated macrophages requires the formate-dependent nitrite reductase regulator-activated ytfE gene

Haemophilus influenzae efficiently colonizes and persists at the human nasopharyngeal mucosa, causing disease when it spreads to other sites. Nitric oxide (NO) represents a major antimicrobial defense deployed by host cells in locations colonized by H. influenzae during pathogenesis that are likely to vary in oxygen levels. Formate-dependent nitrite reductase regulator (FNR) is an oxygen-sensitive regulator in several bacterial pathogens. We report that fnr of H. influenzae is required for anaerobic defense against exposure to NO donors and to resist NO-dependent effects of gamma interferon (IFN-gamma)-activated murine bone marrow-derived macrophages. To understand the mechanism of resistance, we investigated the role of FNR-regulated genes in defense against NO sources. Expression analysis revealed FNR-dependent activation of nrfA, dmsA, napA, and ytfE. Nonpolar deletion mutants of nrfA and ytfE exhibited sensitivity to NO donors, and the ytfE gene was more critical for survival. Compared to the wild-type strain, the ytfE mutant exhibited decreased survival when exposed to macrophages, a defect that was more pronounced after prior stimulation of macrophages with IFN-gamma or lipopolysaccharide. Complementation restored survival of the mutant to the level in the parental strain. Increased sensitivity of the ytfE mutant relative to that of the parent was abrogated by treatment of macrophages with a NO synthase inhibitor, implicating YtfE in resistance to a NO-dependent pathway. These results identify a requirement for FNR in positive control of ytfE and indicate a critical role for ytfE in resistance of H. influenzae to reactive nitrogen species and the antibacterial effects of macrophages.

Association of IS1016 with the hia adhesin gene and biotypes V and I in invasive nontypeable Haemophilus influenzae

A subset of invasive nontypeable Haemophilus influenzae (NTHI) strains has evidence of IS1016, an insertion element associated with division I H. influenzae capsule serotypes. We examined IS1016-positive invasive NTHI isolates collected as part of Active Bacterial Core Surveillance within the Georgia Emerging Infections Program for the presence or absence of hmw1 and hmw2 (two related adhesin genes that are common in NTHI but absent in encapsulated H. influenzae) and hia (homologue of hsf, an encapsulated H. influenzae adhesin gene). Isolates were serotyped using slide agglutination, confirmed as NTHI strains using PCR capsule typing, and biotyped. Two hundred twenty-nine invasive NTHI isolates collected between August 1998 and December 2006 were screened for IS1016; 22/229 (9.6%) were positive. Nineteen of 201 previously identified IS1016-positive invasive NTHI isolates collected between January 1989 and July 1998 were also examined. Forty-one IS1016-positive and 56 randomly selected IS1016-negative invasive NTHI strains were examined. The hia adhesin was present in 39 of 41 (95%) IS1016-positive NTHI strains and 1 of 56 (1.8%) IS1016-negative NTHI strains tested; hmw (hmw1, hmw2, or both) was present in 50 of 56 (89%) IS1016-negative NTHI isolates but in only 5 of 41 (12%; all hmw2) IS1016-positive NTHI isolates. IS1016-positive NTHI strains were more often biotype V (P < 0.001) or biotype I (P = 0.04) than IS1016-negative NTHI strains, which were most often biotype II. Pulsed-field gel electrophoresis revealed the expected genetic diversity of NTHI with some clustering based on IS1016, hmw or hia, and biotypes. A significant association of IS1016 with biotypes V and I and the presence of hia adhesins was found among invasive NTHI. IS1016-positive NTHI strains may represent a unique subset of NTHI strains, with characteristics more closely resembling those of encapsulated H. influenzae.

Induction of beta defensin 2 by NTHi requires TLR2 mediated MyD88 and IRAK-TRAF6-p38MAPK signaling pathway in human middle ear epithelial cells

Background

All mucosal epithelia, including those of the tubotympanium, are secreting a variety of antimicrobial innate immune molecules (AIIMs). In our previous study, we showed the bactericidal/bacteriostatic functions of AIIMs against various otitis media pathogens. Among the AIIMs, human β-defensin 2 is the most potent molecule and is inducible by exposure to inflammatory stimuli such as bacterial components or proinflammatory cytokines. Even though the β-defensin 2 is an important AIIM, the induction mechanism of this molecule has not been clearly established. We believe that this report is the first attempt to elucidate NTHi induced β-defensin expression in airway mucosa, which includes the middle ear.

Methods

Monoclonal antibody blocking method was employed in monitoring the TLR-dependent NTHi response. Two gene knock down methods – dominant negative (DN) plasmid and small interfering RNA (siRNA) – were employed to detect and confirm the involvement of several key genes in the signaling cascade resulting from the NTHi stimulated β-defensin 2 expression in human middle ear epithelial cell (HMEEC-1). The student's t-test was used for the statistical analysis of the data.

Results

The experimental results showed that the major NTHi-specific receptor in HMEEC-1 is the Toll-like receptor 2 (TLR2). Furthermore, recognition of NTHi component(s)/ligand(s) by TLR2, activated the Toll/IL-1 receptor (TIR)-MyD88-IRAK1-TRAF6-MKK3/6-p38 MAPK signal transduction pathway, ultimately leading to the induction of β-defensin 2.

Conclusion

This study found that the induction of β-defensin 2 is highest in whole cell lysate (WCL) preparations of NTHi, suggesting that the ligand(s) responsible for this up-regulation may be soluble macromolecule(s). We also found that this induction takes place through the TLR2 dependent MyD88-IRAK1-TRAF6-p38 MAPK pathway, with the primary response occurring within the first hour of stimulation. In combination with our previous studies showing that IL-1α-induced β-defensin 2 expression takes place through a MyD88-independent Raf-MEK1/2-ERK MAPK pathway, we found that both signaling cascades act synergistically to up-regulate β-defensin 2 levels. We propose that this confers an essential evolutionary advantage to the cells in coping with infections and may serve to amplify the innate immune response through paracrine signaling.

Computer-aided biotechnology: from immuno-informatics to reverse vaccinology

Genome sequences from many organisms, including humans, have been completed, and high-throughput analyses have produced burgeoning volumes of 'omics' data. Bioinformatics is crucial for the management and analysis of such data and is increasingly used to accelerate progress in a wide variety of large-scale and object-specific functional analyses. Refined algorithms enable biotechnologists to follow 'computer-aided strategies' based on experiments driven by high-confidence predictions. In order to address compound problems, current efforts in immuno-informatics and reverse vaccinology are aimed at developing and tuning integrative approaches and user-friendly, automated bioinformatics environments. This will herald a move to 'computer-aided biotechnology': smart projects in which time-consuming and expensive large-scale experimental approaches are progressively replaced by prediction-driven investigations.