Intranasal immunization with a lipooligosaccharide-based conjugate vaccine from nontypeable Haemophilus influenzae enhances bacterial clearance in mouse nasopharynx

Otitis media: recent advances in otitis media vaccine development and model systems

Otitis media is an inflammatory disorder of the middle ear caused by airways-associated bacterial or viral infections. It is one of the most common childhood infections as globally more than 80% of children are diagnosed with acute otitis media by 3 years of age and it is a common reason for doctor's visits, antibiotics prescriptions, and surgery among children. Otitis media is a multifactorial disease with various genetic, immunologic, infectious, and environmental factors predisposing children to develop ear infections. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the most common culprits responsible for acute otitis media. Despite the massive global disease burden, the pathogenesis of otitis media is still unclear and requires extensive future research. Antibiotics are the preferred treatment to cure middle ear infections, however, the antimicrobial resistance rate of common middle ear pathogens has increased considerably over the years. At present, pneumococcal and influenza vaccines are administered as a preventive measure against otitis media, nevertheless, these vaccines are only beneficial in preventing carriage and/or disease caused by vaccine serotypes. Otitis media caused by non-vaccine serotype pneumococci, non-typeable H. influenza, and M. catarrhalis remain an important healthcare burden. The development of multi-species vaccines is an arduous process but is required to reduce the global burden of this disease. Many novel vaccines against S. pneumoniae, non-typeable H. influenza, and M. catarrhalis are in preclinical trials. It is anticipated that these vaccines will lower the disease burden and provide better protection against otitis media. To study disease pathology the rat, mouse, and chinchilla are commonly used to induce experimental acute otitis media to test new therapeutics, including antibiotics and vaccines. Each of these models has its advantages and disadvantages, yet there is still a need to develop an improved animal model providing a better correlated mechanistic understanding of human middle ear infections, thereby underpinning the development of more effective otitis media therapeutics. This review provides an updated summary of current vaccines against otitis media, various animal models of otitis media, their limitations, and some future insights in this field providing a springboard in the development of new animal models and novel vaccines for otitis media.

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.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

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.

Monophosphoryl lipid A enhances nontypeable Haemophilus influenzae-specific mucosal and systemic immune responses by intranasal immunization

OBJECTIVE

Acute otitis media (AOM) is one of the most common infectious diseases in children. Nontypeable Haemophilus influenzae (NTHi) is Gram-negative bacteria that are considered major pathogens of AOM and respiratory tract infections. In this study, we used monophosphoryl lipid A (MPL), a toll-like receptor (TLR) 4 agonist, as an adjuvant to induce mucosal immune responses against NTHi to enhance bacterial clearance from the nasopharynx.

METHODS

Mice were administered 10 μg outer membrane protein (OMP) from NTHi and 0, 10, or 20 μg MPL intranasally once a week for 3 weeks. Control mice were administered phosphate-buffered saline alone. After immunization, these mice were challenged with NTHi. At 6 and 12 h after bacterial challenge, the mice were killed and nasal washes and sera were collected. The numbers of NTHi- and OMP-specific antibodies were quantified by enzyme-linked immunosorbent assay.

RESULTS

The MPL 10 and 20 μg group produced a significant reduction in the number of bacteria recovered from the nasopharynx at 12 h after bacterial challenge compared to the control group. OMP-specific IgA titers were also augmented in the MPL groups compared to the control and OMP groups.

CONCLUSION

MPL is suitable for eliciting effective mucosal immune responses against NTHi in the nasopharynx. These results demonstrate the possibility of an adjuvant that involves stimulation of the innate immune system by TLR4 agonists such as MPL for mucosal vaccination.

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.

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.

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.

Prospects for a vaccine against otitis media

Otitis media is a major cause of morbidity in 80% of all children less than 3 years of age and often goes undiagnosed in the general population. There is evidence to suggest that the incidence of otitis media is increasing. The major cause of otitis media is infection of the middle ear with microbes from the nasopharynx. The anatomical orientation of the eustachian tube, in association with a number of risk factors, predisposes infants and young children to the infection. Bacteria are responsible for approximately 70% of cases of acute otitis media, with Streptococcus pneumoniae, nontypeable Haemophilus influenzae and Moraxella catarrhalis predominating as the causative agents. The respiratory viruses, respiratory syncytial virus, rhinovirus, parainfluenza and influenza, account for 30% of acute otitis media cases. Over the past decade, there has been a profound increase in the reported resistance to antibiotics, which, with increased disease burden, has focussed attention on vaccine development for otitis media. A polymicrobial formulation containing antigens from all major pathogens would have the greatest potential to deliver a sustained reduction in the disease burden globally. The disappointing outcomes for otitis media seen with the polysaccharide pneumococcal conjugate vaccine have raised major challenges for the vaccination strategy. Clearly, more knowledge is required concerning immune mechanisms in the middle ear, as well as vaccine formulations containing antigens that are more representative of the polymicrobial nature of the disease. Antigens that have been extensively tested in animal models are now available for testing in human subjects.

Mechanisms of permanent loss of olfactory receptor neurons induced by the herbicide 2,6-dichlorobenzonitrile: effects on stem cells and noninvolvement of acute induction of the inflammatory cytokine IL-6

We explored the mechanisms underlying the differential effects of two olfactory toxicants, the herbicide 2,6-dichlorobenzonitrile (DCBN) and the anti-thyroid drug methimazole (MMZ), on olfactory receptor neuron (ORN) regeneration in mouse olfactory epithelium (OE). DCBN, but not MMZ, induced inflammation-like pathological changes in OE, and DCBN increased interleukin IL-6 levels in nasal-wash fluid to much greater magnitude and duration than did MMZ. At 24h after DCBN injection, the population of horizontal basal cells (HBCs; reserve, normally quiescent OE stem cells) lining the DMM became severely depleted as some of them detached from the basal lamina, and sloughed into the nasal cavity along with the globose basal cells (GBCs; heterogeneous population of stem and progenitor cells), neurons, and sustentacular cells of the neuroepithelium. In contrast, the layer of HBCs remained intact in MMZ-treated mice, as only the mature elements of the neuroepithelium were shed. Despite the respiratory metaplasia accompanying the greater severity of the DCBN lesion, residual HBCs that survived intoxication were activated by the injury and contributed to the metaplastic respiratory epithelium, as shown by tracing their descendants in a K5CreEr(T2)::fl(stop)TdTomato strain of mice in which recombination causes HBCs to express TdTomato in advance of the lesion. But, contrary to published observations with MMZ, the HBCs failed to form ORNs. A role for IL-6 in suppressing ORN regeneration in DCBN-treated mice was rejected by the failure of the anti-inflammatory drug dexamethasone to prevent the subsequent respiratory metaplasia in the DMM, suggesting that other factors lead to HBC neuro-incompetence.

Immunogenicity of Pasteurella multocida and Mannheimia haemolytica outer membrane vesicles

Pasteurella multocida is able to cause disease in humans and in a wide range of animal hosts, including fowl cholera in birds, atrophic rhinitis in pigs, and snuffles in rabbits. Together with Mannheimia haemolytica, P. multocida also represents a major bacterial causative agent of bovine respiratory disease (BRD), which is one of the most important causes for economic losses for the cattle backgrounding and feedlot industry. Commercially available vaccines only partially prevent infections caused by P. multocida and M. haemolytica. Thus, this study characterized the immunogenicity of P. multocida and M. haemolytica outer membrane vesicles (OMVs) upon intranasal immunization of BALB/c mice. Enzyme-linked immunosorbent assays (ELISA) revealed that OMVs derived from P. multocida or M. haemolytica are able to induce robust humoral and mucosal immune responses against the respective donor strain. In addition, also significant cross-immunogenic potential was observed for both OMV types. Colonization studies showed that a potential protective immune response against P. multocida is not only achieved by immunization with P. multocida OMVs, but also by immunization with OMVs derived from M. haemolytica. Immunoblot and immunoprecipitation analyses demonstrated that M. haemolytica OMVs induce a more complex immune response compared to P. multocida OMVs. The outer membrane proteins OmpA, OmpH, and P6 were identified as the three major immunogenic proteins of P. multocida OMVs. Amongst others, the serotype 1-specific antigen, an uncharacterized outer membrane protein, as well as the outer membrane proteins P2 and OmpA were found to be the most important antigens of M. haemolytica OMVs. These findings are useful for the future development of broad-spectrum OMV based vaccines against BRD and other infections caused by P. multocida or M. haemolytica.

Bioactivation of the nasal toxicant 2,6-dichlorobenzonitrile: an assessment of metabolic activity in human nasal mucosa and identification of indicators of exposure and potential toxicity

The herbicide 2,6-dichlorobenzonitrile (DCBN) is a potent nasal toxicant in rodents; however, it is not known whether DCBN causes similar nasal toxicity in humans. The tissue-selective toxicity of DCBN in mouse nasal mucosa is largely dependent on target tissue bioactivation by CYP2A5. The human orthologues of CYP2A5, CYP2A6 and CYP2A13, are both expressed in nasal mucosa and are capable of activating DCBN. In this study, we directly determined the ability of human nasal mucosa to bioactivate DCBN. We also tested the suitability of a glutathione conjugate of DCBN (GS-DCBN) or its derivatives as biomarkers of DCBN exposure and nasal toxicity in mouse models. We found that human fetal nasal mucosa microsomes catalyze the formation of GS-DCBN, with a Km value comparable to that of adult mouse nasal mucosa microsomes. The activity of the human nasal mucosa microsomes was inhibited by 8-methoxypsoralen, a known CYP2A inhibitor. GS-DCBN and its metabolites were detected in the nasal mucosa and nasal-wash fluid obtained from DCBN-treated mice, in amounts that increased with escalations in DCBN dose, and they were all still detectable at 24 h after a DCBN treatment (at 10 mg/kg). Further studies in Cyp2a5-null mice indicated that GS-DCBN and its metabolites in nasal-wash fluid were generated in the nasal mucosa, rather than in other organs. Thus, our data indicate for the first time that the human nasal mucosa is capable of bioactivating DCBN and that GS-DCBN and its metabolites in nasal-wash fluid may collectively serve as indicators of DCBN exposure and potential nasal toxicity in humans.

Intranasal immunization with nontypeable Haemophilus influenzae outer membrane vesicles induces cross-protective immunity in mice

Haemophilus influenzae is a Gram-negative human-restricted bacterium that can act as a commensal and a pathogen of the respiratory tract. Especially nontypeable H. influenzae (NTHi) is a major threat to public health and is responsible for several infectious diseases in humans, such as pneumonia, sinusitis, and otitis media. Additionally, NTHi strains are highly associated with exacerbations in patients suffering from chronic obstructive pulmonary disease. Currently, there is no licensed vaccine against NTHi commercially available. Thus, this study investigated the utilization of outer membrane vesicles (OMVs) as a potential vaccine candidate against NTHi infections. We analyzed the immunogenic and protective properties of OMVs derived from various NTHi strains by means of nasopharyngeal immunization and colonization studies with BALB/c mice. The results presented herein demonstrate that an intranasal immunization with NTHi OMVs results in a robust and complex humoral and mucosal immune response. Immunoprecipitation revealed the most important immunogenic proteins, such as the heme utilization protein, protective surface antigen D15, heme binding protein A, and the outer membrane proteins P1, P2, P5 and P6. The induced immune response conferred not only protection against colonization with a homologous NTHi strain, which served as an OMV donor for the immunization mixtures, but also against a heterologous NTHi strain, whose OMVs were not part of the immunization mixtures. These findings indicate that OMVs derived from NTHi strains have a high potential to act as a vaccine against NTHi infections.

Monophosphoryl lipid A induced innate immune responses via TLR4 to enhance clearance of nontypeable Haemophilus influenzae and Moraxella catarrhalis from the nasopharynx in mice

Acute otitis media (AOM) is one of the most common infectious diseases in children. Nontypeable Haemophilus influenzae (NTHi) and Moraxella catarrhalis, Gram-negative bacteria, are considered major pathogens of AOM and respiratory tract infections. In this study, we used monophosphoryl lipid A (MPL) as a Toll-like receptor (TLR4) agonist to induce innate immune responses before challenge with NTHi and M. catarrhalis to enhance bacterial clearance from the nasopharynx. Mice were intranasally administered 40, 10, or 1 μg of MPL and challenged with NTHi and M. catarrhalis 12 and 24 h later. At 6 and 12 h after the bacterial challenge, the mice were killed and nasal washes were collected. The numbers of NTHi, M. catarrhalis, and inflammatory cells were quantitated. Inoculation of MPL produced a significant reduction in the number of bacteria recovered from the nasopharynx at 6 and/or 12 h after the bacterial challenge, when compared with control mice. The effect was dose dependent. MPL inoculation also induced the early accumulation of neutrophils in the nasopharynx after exposure to bacteria. MPL is effective for eliciting clearance of both NTHi and M. catarrhalis from the nasopharynx. These results indicate the possibility of a new strategy against Gram-negative bacterial infection that involves the stimulation of the innate immune system by TLR4 agonists such as MPL.

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.

Protection against nontypeable Haemophilus influenzae challenges by mucosal vaccination with a detoxified lipooligosaccharide conjugate in two chinchilla models

Otitis media (OM) can occur following outset of upper respiratory tract infections. Inhibition of bacterial colonization in nasopharynx (NP) by mucosal vaccination may prevent OM by reducing bacterial invasion of the middle ears (MEs). In this study, 80 chinchillas were intranasally (i.n.) immunized with a detoxified lipooligosaccharide (dLOS)-tetanus toxoid conjugate vaccine of nontypeable Haemophilus influenzae (NTHi) mixed with cholera toxin (CT) or CT alone. All vaccinated animals responded with elevated levels of mucosal and serum anti-LOS antibodies. Two weeks after the last immunization, 40 chinchillas were challenged i.n. with NTHi to evaluate NP colonization and ME infection while the rest of the animals were challenged transbullarly (T.B.) to examine the development of OM. Compared to the control group, the vaccination inhibited not only bacterial colonization in NP and transmission to MEs in the i.n. challenge group but also bacterial colonization in NP and transmission to unchallenged ears in the T.B. challenge group. Though no difference was found in the challenged ears of either group right after the T.B. challenge, an early clearance of NTHi from NP and unchallenged ears as well as less severity of OM in the unchallenged ears were observed in vaccinated animals. Current results along with our previous data indicate that mucosal vaccination is capable of inhibiting NTHi NP colonization and preventing OM occurrence in chinchillas; the i.n. challenge model is preferable for testing the mucosal vaccines while the T.B. challenge model is superior for testing the systemic vaccines.

Intranasal administration of a detoxified endotoxin vaccine protects mice against heterologous Gram-negative bacterial pneumonia

When given passively or elicited actively, antibodies induced by a detoxified Escherichia coli J5 mutant lipopolysaccharide (J5dLPS)-group B meningococcal outer membrane protein (-OMP) vaccine previously protected animals from lethal sepsis. To assess the use of this vaccine for the treatment of Gram-negative bacillary pneumonia, we vaccinated mice, with or without the adjuvant CpG, by intranasal (i.n.) or intraperitoneal (i.p.) routes of administration. Local and systemic IgG levels were 2-3 logs higher following i.p. immunization compared to i.n. However, i.n. immunization elicited both local and systemic IgA, unlike i.p. administration. The addition of CpG to the vaccine, by either route of administration, elicited greater levels of antibody. Intranasal immunization protected mice against lethal heterologous Gram-negative bacillary pneumonia and post-immunization serum and broncho-alveolar lavage fluid mediated enhanced bacterial killing with peritoneal and alveolar macrophages in vitro. We conclude that further studies on the use of J5dLPS-OMP for the prevention of nosocomial pneumonia are warranted.

Mouse models of otitis media

PURPOSE OF REVIEW

Otitis media is one of the most prevalent inflammatory diseases in the pediatric population. The personal and societal costs for otitis media are significant. Problems arising from antibiotic use have led to considerable animal research efforts to better understand the mechanisms of acute otitis media and to develop new strategies for its prevention and treatment.

RECENT FINDINGS

Various animal models induce acute otitis media from a variety of interventions, including direct injection of whole bacteria or their products into the middle ear. The mouse model has begun to emerge as a model for otitis media. The mouse affords many advantages for in-vivo research, including ease of genetic manipulation, availability of numerous inbred and transgenic strains, and an extensively studied immune system. Experimental reagents for cellular and molecular studies are widely available for the mouse. The mouse is an excellent model for investigating the genetics and molecular bases for otitis media due to the extensive understanding of the mouse genome.

SUMMARY

With the increased availability of knockout and transgenic mice, and the large amount of data to indicate that human disease is accurately modeled in the mouse, the mouse model is increasingly becoming a model of choice.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Bactericidal Monoclonal Antibody Against Moraxella catarrhalis Lipooligosaccharide Cross-Reacts with Haemophilus Spp

Monoclonal antibodies (MAbs) against lipooligosaccharide (LOS) determinants after immunization of BALB/c mice with heat inactivated Moraxella catarrhalis serotype A were generated. MAb 219A9 was specific for a common epitope of A, B, and C M. catarrhalis serotypes in ELISA and immunofluorescent test (IFT). In both tests it also cross-reacted with whole bacteria and LPS antigens isolated from non-typeable H. influenzae and H. parainfluenzae strains. IgM antibody clone 219A9 possessed a strong bactericidal effect against the three serotypes in the presence of complement. Our results demonstrate that antibodies directed to a single LOS epitope common for A, B, and C serotype could be highly protective. This suggests that the common determinants are very promising in the development of LOS-based vaccine against M. catarrhalis. The cross-reactions of MAb 219A9 with Haemophilus spp. also show that immunization could result in immune response to epitopes conserved in other important respiratory pathogens.

Kinetics of mouse antibody and lymphocyte responses during intranasal vaccination with a lipooligosaccharide-based conjugate vaccine

We investigated the kinetics of humoral immunity and its related cellular immune responses to intranasal (IN) immunization with a detoxified lipooligosaccharide (dLOS)-tetanus toxoid (TT) conjugate against nontypeable Haemophilus influenzae (NTHi) in mice. IN vaccination with dLOS-TT elicited high titers of LOS-specific IgA in nasal washes and IgG in sera during a course of 4 inoculations while high titers of TT-specific IgA and IgG were found in sera. A significant increase of LOS-specific IgA antibody forming cells (AFCs) was observed in nasopharyngeal-associated lymphoid tissue (NALT) and nasal passages. However, TT induced broad responses with higher numbers of IgA and IgG AFCs found in NALT and nasal passages, less but significant IgA AFCs in cervical lymphoid nodes (CLN), spleen, and lungs. Phenotypic analysis revealed a significant rise of total B220+ B-lymphocytes in NALT and CLN, particularly a rise in IgA+/IgM+ cells in the NALT after the immunization. The latter result was complied with a significant rise of IL-4 but not IFN-gamma positive CD4+ T-lymphocytes in NALT. Analysis of IgG antibody subclasses showed that an IgG1 response to both LOS and TT epitopes dominated in serum when compared to IgG2a. These kinetic antibody patterns and cellular responses may provide useful information regarding to effective mucosal vaccines against NTHi infections.

Intranasal immunisation with conjugate vaccine protects mice from systemic and respiratory tract infection with Pseudomonas aeruginosa

We tested intranasal application of anti-Pseudomonas conjugate vaccine in mice. Comparison of immunisation via the intra-muscular versus intranasal routes showed the induction of equivalent levels of specific serum IgG and IgG subclasses antibodies if cholera toxin was used as an adjuvant. In contrast, secretion of specific mucosal IgA antibodies in the upper respiratory tract was only observed after intranasal immunisation together with adjuvant. Systemic and mucosal immunity was also established via the intranasal route when CpG-containing oligonucleotides were used as adjuvant. The functionality of intranasally induced antibodies was proven in vitro by opsonophagocytosis and in vivo using the burn-wound sepsis and intra-tracheal lung infection models. These results demonstrate the feasibility of intranasal immunisation against P. aeruginosa with conjugate vaccine.

Intranasal immunization with a colloid-formulated bacterial extract induces an acute inflammatory response in the lungs and elicits specific immune responses

Nonspecific stimulation of lung defenses by repeated oral administration of immunomodulators, such as bacterial extracts, has shown potential for the prevention of respiratory tract infections. Here, we show that intranasal (i.n.) immunization with a bacterial extract formulated as a colloid induces an acute inflammatory response in the lungs characterized by increased production of CCL and CXCL chemokines and a major influx of dendritic cells (DCs) and neutrophils, with a higher proportion of DCs showing an activated phenotype (high CD80/CD86 expression). Cytokine levels measured in bronchoalveolar-lavage samples showed a small increase in the production of tumor necrosis factor alpha and similar levels of the other cytokines measured (interleukin 10 [IL-10], IL-12, and gamma interferon [IFN-gamma]) in immunized mice compared with control mice. However, the recall response of primed animals after antigenic challenge induced increased expression of IL-12 and IFN-gamma mRNAs in lung homogenates. Overall, all these effects were not due to the lipopolysaccharide content in the bacterial extract. Furthermore, we found that three i.n. doses administered 2 to 3 weeks apart were enough to elicit long-lasting specific serum immunoglobulin G (IgG) and secretory IgA antibody responses. Assessment of IgG subclasses showed a balanced pattern of IgG1-IgG2a responses. The serum total IgE concentrations were also elevated in immunized mice 2 weeks after the third dose, but they significantly decreased soon afterwards. Our results suggest that simple formulations of bacterial extracts administered i.n. are highly immunogenic, eliciting local and systemic immune responses, and may serve as the basis for cost-effective immunotherapies for the prevention and treatment of respiratory infections.