Cellular immunity to the P6 outer membrane protein of nontypeable Haemophilus influenzae

Identification of human T-cell epitopes and highly immunogenic analog peptides on the non-typeable Haemophilus influenzae P6 outer membrane protein

P6 outer membrane protein is one of the candidates for a vaccine formulation against non-typeable Haemophilus influenzae (NTHi) infection. However, otitis-prone children who have recurrent episodes of acute otitis media due to NTHi fail to respond adequately to P6. An innovative approach to vaccination is therefore required to augment such children's immune response. To develop an effective peptide vaccine, we established P6-specific CD4(+) T-cell lines (TCLs) restricted by the human histocompatibility leukocyte antigen (HLA)-DR9 molecule, and revealed a human T-cell epitope on P6 and its core peptide sequence (p77-85; EYNIALGQR). Furthermore, we found that 3 analog peptides, E77D (the substitution of E at position 77 with D), N79G, and R85K, induced high proliferative responses as well as marked cytokine production when compared to the T-cell epitope peptide. These peptides may be candidates for a peptide vaccine formulation effective against NTHi infections, even in otitis-prone children.

T cell cytokine responses to outer membrane proteins of Haemophilus influenzae and the house dust mite allergens Der p 1 in allergic and non-allergic subjects

BACKGROUND

Haemophilus influenzae are ubiquitous colonizers of the nasopharynx, Little is known about the T cell cytokine responses to the antigens of these bacteria and whether or not the responses may interact with responses to aeroallergen.

OBJECTIVE

To measure the T cell cytokine responses to conserved outer membrane protein antigens of Haemophilus influenzae and to house dust mite allergen of subjects allergic to the house dust mite and of subjects without allergic sensitization.

METHODS

T cell responses were measured by in vitro proliferation and cytokine release from peripheral blood monocytes (PBMC). The allergen used was Der p 1 and outer membrane proteins were recombinant polypeptides representing the OMP6 and D15 antigens.

RESULTS

The PBMC of most subjects had proliferative responses to OMP6 and D15, which were highly correlated. The pattern of cytokine release was Th1 biased with high levels of IFN-gamma and usually little IL-5 or IL-13 although PBMC from a few subjects did release IL-5 independent of allergic status. IL-10 release was readily detected. There was no difference in the anti-OMP cytokine response of PBMC from subjects without any known allergy and the responses of PBMC from subjects who were highly allergic to house dust mite. The responses to the Der p 1 allergen showed the expected Th2 cytokine release.

CONCLUSION

The outer membrane protein antigens of the ubiquitous colonizing bacteria Haemophilus influenzae induce Th1 cytokine responses which are similar for PBMC from non-allergic individuals and subjects with a high degree of allergy to the perennial house dust mite allergen and strong Th2 responses to Der p 1.

Intranasal immunization enhances clearance of nontypeable Haemophilus influenzae and reduces stimulation of tumor necrosis factor alpha production in the murine model of otitis media

Nontypeable Haemophilus influenzae (NTHi) is a major pathogen causing otitis media (OM). One of the outer membrane proteins of NTHi, P6, is a common antigen to all strains and is considered a candidate for mucosal vaccine. We have previously reported that intranasal immunization with P6 and cholera toxin (CT) could induce P6-specific immunoglobulin A (IgA) antibodies in the middle ear. In the present study, we assessed the effect of intranasal immunization for the protection against NTHi-induced OM. Mice were immunized intranasally with P6 and CT as an adjuvant on days 0, 7, and 14. Control mice were given phosphate-buffered saline (PBS) without antigen. One week after the final immunization, a suspension of live NTHi (10(7) CFU) was injected into the tympanic cavity to induce experimental OM. On days 3 and 7 after bacterial challenge, mice were killed and middle ear effusions (MEEs) were collected. All immunized mice showed elevated titers of P6-specific antibodies in MEEs. The rank order of specific antibody included, from highest to lowest levels, IgG, IgA, and IgM. In addition, immunized mice showed enhanced clearance of NTHi from the middle ear and the number of NTHi in MEEs of immunized mice was reduced by 97% on day 3 and by 92% on day 7 after bacterial challenge relative the number in the MEEs of control mice. The protective effect of intranasal immunization on the incidence of NTHi-induced experimental OM was evident on day 7 after challenge. By day 7, the number of MEEs in immunized mice was 64% less than that in control mice and the incidence of NTHi culture-positive MEEs in immunized mice was 56% less than that in control mice. Less stimulation of tumor necrosis factor alpha (TNF-alpha) production in the middle ear was evident on day 3 after challenge. Immunized mice showed lower concentrations of TNF-alpha in MEEs. These results indicate that intranasal immunization affords protection against experimental OM as evidenced by enhanced clearance of NTHi and less stimulation of TNF-alpha production in the middle ear. These findings suggest that a nasal vaccine might be useful for preventing OM.

Induction of specific immunoglobulin A and Th2 immune responses to P6 outer membrane protein of nontypeable Haemophilus influenzae in middle ear mucosa by intranasal immunization

Nontypeable Haemophilus influenzae (NTHI) is a major pathogen of otitis media. One of the outer membrane proteins of NTHI, P6, is an antigen common to all strains and is considered as a candidate for mucosal vaccine. To elucidate the possibility of developing a nasal vaccine against nontypeable Haemophilus influenzae (NTHI) and to investigate mucosal immune responses in the middle ear, mice were immunized intranasally with the P6 outer membrane protein of NTHI, and P6-specific immune responses in the middle ear mucosa were examined. Mice were given with P6 and cholera toxin intranasally as an adjuvant on days 0, 7, and 14 and were killed on day 21. The P6-specific immunoglobulin A (IgA) antibody titer in ear wash was significantly elevated. Mononuclear cells were isolated from middle ear mucosa, and an increase in P6-specific IgA-producing cells was shown with an enzyme-linked immunospot assay. In addition, an increase in memory T cells in middle ear mucosa was detected with flow cytometric analysis after intranasal immunization. Moreover, in vitro stimulation with P6 resulted in proliferation of purified CD4(+) T cells from immunized mice, and these T cells expressed Th2 cytokine mRNA. These results indicate that P6-specific IgA-B-cell immune responses and selected Th2 cytokine expressing Th cells were induced in middle ear mucosa by intranasal immunization. These findings suggest that a nasal vaccine is useful for preventing otitis media with effusion.

Antibody responses to the outer membrane protein P6 of non-typeable Haemophilus influenzae and pneumococcal capsular polysaccharides in otitis-prone children

Acute otitis media (AOM) is a common infectious disease in children. Some children experience recurrent episodes of AOM. Recent investigations demonstrate antigen-specific immunological deficiencies in children prone to AOM. In the present study, the immune responses to non-typeable Haemophilus influenzae (NTHi) and Streptococcus pneumoniae (S. pneumoniae) were further investigated in otitis-prone children and normal children. Forty-eight percent of otitis-prone children exhibited reduced IgG2 levels to S. pneumoniae and 55% exhibited reduced IgG levels to NTHi. These data suggest that otitis proneness appears to be related to numerous immunological derangements. Pathogen-specific antibodies are a reliable measure of otitis proneness.

Cellular immune response of adenoidal and tonsillar lymphocytes to the P6 outer membrane protein of non-typeable Haemophilus influenzae and its relation to otitis media

Cellular immune responses to the P6 outer membrane protein of non-typeable Haemophilus influenzae (NTHi) were determined in vitro by measuring immunoglobulin (Ig) secreting cells and lymphocyte proliferation in adenoidal and tonsillar lymphocytes from 19 children. Preliminary tests showed that P6 did not stimulate naive cells such as cord blood lymphocytes, but did stimulate sensitized cells in adenoids and tonsils. Cellular proliferation was significantly higher in adenoidal lymphocytes than in tonsillar lymphocytes (median: quadratile of stimulation index = 3.7:2.3-5.5 vs. 1.2:1.0-2.1, p < 0.02). A comparison between children with or without otitis media revealed that proliferative responses to P6 of adenoidal lymphocytes from children with otitis media were significantly decreased (2.0:1.8-3.6 vs. 3.7:2.3-5.5, p < 0.04). P6-specific antibody secreting cells were identified in a total of 14 adenoids and the number of cells secreting IgA was decreased in the otitis media group compared to controls (median: quadratile/10(6) cells = 435:359-499 vs. 755:593-1870, p < 0.05). Cultivation with P6 stimulated IgA secretion in children without otitis media, while no response was seen in children with otitis media (median: quadratile/10(6) cells = 1323:915-2410 vs. 2240:1900-2830, p < 0.02). These preliminary data demonstrate that lymphocytes from adenoids and tonsils recognize P6 as a specific antigen and that the adenoid is the more reactive of the two organs. Impaired P6-specific cellular immune responses of adenoids in children with otitis media may explain the recurrent nature of otitis media due to NTHi in the otitis prone population.

Characteristics of the immunological response in the clearance of non-typeable Haemophilus influenzae from the lung

Clearance of non-typeable Haemophilus influenzae (NTHi) from the respiratory tract was investigated, over time, in immune and non-immune rats. A triphasic pattern characterized the clearance of bacteria from the lungs. Mucosal immunization enhanced bacterial clearance from the lungs in each of the three phases compared with clearance from non-immunized animals. Total clearance of bacteria was observed from lung tissue by 12 h in immune animals and 24 h in non-immune animals. Polymorphonuclear leucocytes not only arrived earlier and initially in greater numbers, but disappeared earlier in immune animals (peaking at 8 h post-challenge), compared with non-immune animals (peaking at 12h post-challenge). Systemically derived and locally produced NTHi-specific IgA and IgG correlated with enhanced bacterial clearance during the secondary phase. This model demonstrates that immunized animals up-regulate and resolve inflammatory responses to pulmonary infection more rapidly than the non-immunized controls.

Immune responses of adenoidal lymphocytes specific to Haemophilus influenzae in the nasopharynx

OBJECTIVES

Investigate immune responses of adenoidal lymphocytes against outer-membrane protein P6 purified from nontypeable Haemophilus influenzae (HI). Clarify the role of adenoids in regulating the colonization of HI in the nasopharynx.

STUDY DESIGN

Microbiological and immunological examinations of adenoids obtained from 21 children, 15 boys and five girls, from 1 to 13 years of age (median, 5 y), suffering from adenoidal hypertrophy complicated by otitis media with effusion (OME).

METHODS

The incidence of HI in adenoids was compared with the number of P6-specific immunoglobulin (Ig) A-secreting cells in adenoids, determined by enzyme-linked immunoassay.

RESULTS

Quantitative culture assay showed significant correlation between the numbers of HI in adenoids and those in nasopharyngeal secretions (NS). In children aged 5 years and younger, the numbers of P6-specific IgA-secreting cells in adenoids were significantly correlated with IgA antibody titers in NS (r = 0.68, P < .05). The numbers of P6-specific IgG- and IgA-secreting cells were lower in children aged 6 years and older than in children aged 5 years and younger. Furthermore, the number of P6-specific IgA-secreting cells was significantly increased in HI-negative subjects when compared with HI-positive subjects (P < .05).

CONCLUSIONS

Adenoids play an important role as an effector site of the mucosal immune system in the upper respiratory tract. IgA immune responses in adenoids are responsible for the clearance of HI from the nasopharynx.