Characterization of antigens from nontypable Haemophilus influenzae recognized by human bactericidal antibodies. Role of Haemophilus outer membrane proteins

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.

Phase variation and host immunity against high molecular weight (HMW) adhesins shape population dynamics of nontypeable Haemophilus influenzae within human hosts

Nontypeable Haemophilus influenzae (NTHi) is a bacterium that resides within the human pharynx. Because NTHi is human-restricted, its long-term survival is dependent upon its ability to successfully colonize new hosts. Adherence to host epithelium, mediated by bacterial adhesins, is one of the first steps in NTHi colonization. NTHi express several adhesins, including the high molecular weight (HMW) adhesins that mediate attachment to the respiratory epithelium where they interact with the host immune system to elicit a strong humoral response. hmwA, which encodes the HMW adhesin, undergoes phase variation mediated by 7-base pair tandem repeats located within its promoter region. Repeat number affects both hmwA transcription and HMW-adhesin production such that as the number of repeats increases, adhesin production decreases. Cells expressing large amounts of HMW adhesins may be critical for the establishment and maintenance of NTHi colonization, but they might also incur greater fitness costs when faced with an adhesin-specific antibody-mediated immune response. We hypothesized that the occurrence of large deletion events within the hmwA repeat region allows NTHi cells to maintain adherence in the presence of antibody-mediated immunity. To study this, we developed a mathematical model, incorporating hmwA phase variation and antibody-mediated immunity, to explore the trade-off between bacterial adherence and immune evasion. The model predicts that antibody levels and avidity, catastrophic loss rates, and population carrying capacity all significantly affected numbers of adherent NTHi cells within a host. These results suggest that the occurrence of large, yet rare, deletion events allows for stable maintenance of a small population of adherent cells in spite of HMW adhesin specific antibody-mediated immunity. These adherent subpopulations may be important for sustaining colonization and/or maintaining transmission.

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.

Outer membrane protein P5 is required for resistance of nontypeable Haemophilus influenzae to both the classical and alternative complement pathways

The complement system is an important first line of defense against the human pathogen Haemophilus influenzae. To survive and propagate in vivo, H. influenzae has evolved mechanisms for subverting this host defense, most of which have been shown to involve outer surface structures, including lipooligosaccharide glycans and outer surface proteins. Bacterial defense against complement acts at multiple steps in the pathway by mechanisms that are not fully understood. Here we identify outer membrane protein P5 as an essential factor in serum resistance of both H. influenzae strain Rd and nontypeable H. influenzae (NTHi) clinical isolate NT127. P5 was essential for resistance of Rd and NT127 to complement in pooled human serum. Further investigation determined that P5 expression decreased cell surface binding of IgM, a potent activator of the classical pathway of complement, to both Rd and NT127. Additionally, P5 expression was required for NT127 to bind factor H (fH), an important inhibitor of alternative pathway (AP) activation. Collectively, the results obtained in this work highlight the ability of H. influenzae to utilize a single protein to perform multiple protective functions for evading host immunity.

Anti-superoxide dismutase antibodies are associated with survival in patients with sporadic amyotrophic lateral sclerosis

Our objective was to test the hypothesis that aberrantly modified forms of superoxide dismutase (SOD1) influence the disease course for sporadic amyotrophic lateral sclerosis (SALS). We probed for anti-SOD1 antibodies (IgM and IgG) against both the normal and aberrantly oxidized-SOD1 (SODox) antigens in sera from patients with SALS, subjects diagnosed with other neurological disorders and healthy individuals, and correlated the levels of these antibodies to disease duration and/or severity. Anti-SOD1 antibodies were detected in all cohorts; however, a subset of ∼5-10% of SALS cases exhibited elevated levels of anti-SOD1 antibodies. Those SALS cases with relatively high levels of IgM antibodies against SODox exhibit a longer survival of 6.4 years, compared to subjects lacking these antibodies. By contrast, SALS subjects expressing higher levels of IgG antibodies reactive for the normal WT-SOD1 antigen exhibit a shorter survival of 4.1 years. Anti-SOD1 antibody levels did not correlate with disease severity in either the Alzheimer's or Parkinson's disease cohorts. In conclusion, the association of longer survival with elevated levels of anti-SODox antibodies suggests that these antibodies may be protective. By extension, these data implicate aberrantly modified forms of WT-SOD1 (e.g. oxidized SOD1) in SALS pathogenesis. In contrast, an immune response against the normal WT-SOD1 appears to be disadvantageous in SALS, possibly because the anti-oxidizing activity of normal WT-SOD1 is beneficial to SALS individuals.

The meningococcal vaccine candidate neisserial surface protein A (NspA) binds to factor H and enhances meningococcal resistance to complement

Complement forms an important arm of innate immunity against invasive meningococcal infections. Binding of the alternative complement pathway inhibitor factor H (fH) to fH-binding protein (fHbp) is one mechanism meningococci employ to limit complement activation on the bacterial surface. fHbp is a leading vaccine candidate against group B Neisseria meningitidis. Novel mechanisms that meningococci employ to bind fH could undermine the efficacy of fHbp-based vaccines. We observed that fHbp deletion mutants of some meningococcal strains showed residual fH binding suggesting the presence of a second receptor for fH. Ligand overlay immunoblotting using membrane fractions from one such strain showed that fH bound to a ∼17 kD protein, identified by MALDI-TOF analysis as Neisserial surface protein A (NspA), a meningococcal vaccine candidate whose function has not been defined. Deleting nspA, in the background of fHbp deletion mutants, abrogated fH binding and mAbs against NspA blocked fH binding, confirming NspA as a fH binding molecule on intact bacteria. NspA expression levels vary among strains and expression correlated with the level of fH binding; over-expressing NspA enhanced fH binding to bacteria. Progressive truncation of the heptose (Hep) I chain of lipooligosaccharide (LOS), or sialylation of lacto-N-neotetraose LOS both increased fH binding to NspA-expressing meningococci, while expression of capsule reduced fH binding to the strains tested. Similar to fHbp, binding of NspA to fH was human-specific and occurred through fH domains 6–7. Consistent with its ability to bind fH, deleting NspA increased C3 deposition and resulted in increased complement-dependent killing. Collectively, these data identify a key complement evasion mechanism with important implications for ongoing efforts to develop meningococcal vaccines that employ fHbp as one of its components.

Neisseria meningitidis is an important cause of bacterial meningitis and sepsis worldwide. The complement system is a family of proteins that is critical for innate immune defenses against this pathogen. In order to successfully colonize humans and cause disease, the meningococcus must escape killing by the complement system. In this study we show that meningococci can use one of its surface proteins called Neisserial surface protein A (NspA) to bind to a host complement inhibitory protein called factor H (fH). NspA is a protein vaccine candidate against group B meningococcal disease. Binding of fH limits complement activation on the bacterial surface and enhances the ability of the meningococcus to resist complement-dependent killing. Capsular polysaccharide expression decreases fH binding to NspA, while truncation of the core glycan chain of lipooligosaccharide increases fH binding to meningococcal NspA. Loss of NspA results in enhanced complement activation on the bacterial surface and increased complement-dependent killing of meningococci. Our findings have disclosed a novel function for NspA and sheds further light on how this pathogen evades killing by the complement system.

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.

Systemic humoral immunity to non-typeable Haemophilus influenzae

Non-typeable Haemophilus influenzae (NTHi) is a major cause of respiratory but rarely systemic infection. The host defence to this bacterium has not been well defined in patients with chronic airway infection. The aim of this study was to assess the effect of humoral immunity in host defence to NTHi. Responses were measured in control and bronchiectasis subjects who had recurrent bronchial infection. Antibody and complement-mediated killing was assessed by incubating NTHi with serum and the role of the membrane-attack complex and classical/alternate pathways of complement activation measured. The effect of one strain to induce protective immunity against other strains was assessed. The effect of antibody on granulocyte intracellular killing of NTHi was also measured. The results showed that both healthy control subjects and bronchiectasis patients all had detectable antibody to NTHi of similar titre. Both groups demonstrated effective antibody/complement-mediated killing of different strains of NTHi. This killing was mediated through the membrane-attack complex and the classical pathway of complement activation. Immunization of rabbits with one strain of NTHi resulted in protection from other strains in vitro. Antibody activated granulocytes to kill intracellular bacteria. These findings may explain why NTHi rarely causes systemic disease in patients with chronic respiratory mucosal infection and emphasize the potential importance of cellular immunity against this bacterium.

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

The HMW1/HMW2-like adhesion proteins of nontypeable Haemophilus influenzae (NTHI) are expressed by 75% of NTHI strains. Antibodies directed against these proteins are opsonophagocytic in vitro and are protective in an animal model of infection. The objective of the present study was to determine the opsonophagocytic activity of high-titer anti-HMW1/HMW2 immune sera against both homologous and heterologous NTHI strains. Chinchillas were immunized with purified HMW1/HMW2-like proteins from five prototype NTHI strains. Serum opsonophagocytic activity was monitored in an assay that uses a human promyelocytic cell line, HL-60, as the source of phagocytic cells. Preimmune sera did not demonstrate opsonophagocytic killing of any strains. In contrast, the immune sera demonstrated killing of the five homologous NTHI strains at titers ranging from 1:320 to 1:640. The immune sera also demonstrated killing of eight heterologous NTHI strains that express HMW1/HMW2-like proteins at titers ranging from 0 to 1:640. Killing of heterologous strains sometimes demonstrated a prozone phenomenon. None of the immune sera killed NTHI strains that did not express HMW1/HMW2-like proteins. Adsorption of immune sera with HMW1/HMW2-like proteins purified from either homologous or heterologous NTHI strains eliminated opsonophagocytic killing of homologous strains in most cases. These data demonstrate that antibodies produced following immunization with the HMW1/HMW2-like proteins are opsonophagocytic for both homologous and heterologous NTHI and strongly suggest that common epitopes recognized by functionally active antibodies exist on the HMW1/HMW2-like proteins of unrelated NTHI strains. The results argue for the continued investigation of the HMW1/HMW2-like proteins as potential vaccine candidates for the prevention of NTHI disease.

The meningococcal vaccine candidate GNA1870 binds the complement regulatory protein factor H and enhances serum resistance

Neisseria meningitidis binds factor H (fH), a key regulator of the alternative complement pathway. A approximately 29 kD fH-binding protein expressed in the meningococcal outer membrane was identified by mass spectrometry as GNA1870, a lipoprotein currently under evaluation as a broad-spectrum meningococcal vaccine candidate. GNA1870 was confirmed as the fH ligand on intact bacteria by 1) abrogation of fH binding upon deleting GNA1870, and 2) blocking fH binding by anti-GNA1870 mAbs. fH bound to whole bacteria and purified rGNA1870 representing each of the three variant GNA1870 families. We showed that the amount of fH binding correlated with the level of bacterial GNA1870 expression. High levels of variant 1 GNA1870 expression (either by allelic replacement of gna1870 or by plasmid-driven high-level expression) in strains that otherwise were low-level GNA1870 expressers (and bound low amounts of fH by flow cytometry) restored high levels of fH binding. Diminished fH binding to the GNA1870 deletion mutants was accompanied by enhanced C3 binding and increased killing of the mutants. Conversely, high levels of GNA1870 expression and fH binding enhanced serum resistance. Our findings support the hypothesis that inhibiting the binding of a complement down-regulator protein to the neisserial surface by specific Ab may enhance intrinsic bactericidal activity of the Ab, resulting in two distinct mechanisms of Ab-mediated vaccine efficacy. These data provide further support for inclusion of this molecule in a meningococcal vaccine. To reflect the critical function of this molecule, we suggest calling it fH-binding protein.

Eustachian tube possesses immunological characteristics as a mucosal effector site and responds to P6 outer membrane protein of nontypeable Haemophilus influenzae

The eustachian tube (ET) plays an important role in the pathogenesis of otitis media (OM). To better understand its biology and to develop a nasal vaccine for preventing OM, mucosal lymphocytes in the ET were analyzed, and the ET's immunological function was investigated. Mononuclear cells were isolated from murine ET, and lymphocyte subsets were analyzed by flow cytometry. Antibody-producing cells were determined by enzyme-linked immunospot assay. The expression of cytokine mRNA in ET CD4(+) T cells was determined by RT-PCR. Results in naive mice showed that the ET contained many immunocompetent cells, including a relative large number of IgA-producing cells and Th2 cytokine-expressing T cells. Next, we investigated antigen-specific immune responses in the ET. Mice were immunized intranasally with the P6 outer membrane of nontypeable Haemophilus influenzae (NTHi) and cholera toxin (CT), and P6-specific immune responses in the ET were examined. P6-specific IgA producing cells markedly increased in the ET. Moreover, in vitro stimulation with P6 of purified CD4(+) T cells from immunized mice resulted in the proliferation of CD4(+) T cells that expressed Th2 cytokine mRNA. These results indicate that the ET might be characterized as a mucosal effector site and that antigen-specific IgA and Th2 immune responses could be induced in the ET by intranasal immunization. These findings suggest that the ET might be a key immunological organ in the pathogenesis of OM, and in the development of a nasal vaccine.

Characterization of a peptide vaccine candidate mimicking an oligosaccharide epitope of Neisseria gonorrhoeae and resultant immune responses and function

The 2C7 epitope is a conserved oligosaccharide structure, a part of lipooligosaccharide (LOS) on Neisseria gonorrhoeae, present in 95% of clinical gonococcal isolates. 2C7 may represent a potential candidate for an anti-gonococcal vaccine. To circumvent the limitations of saccharide immunogens in producing long lived immune responses, we identified a peptide that mimics the 2C7 epitope using a random peptide library, characterizing linear and cyclic forms and formulating a multiple antigenic peptide. The multiple antigenic peptide Octa-MAP1 was used for immunization, and elicited >or=4-fold increase in cross-reactive anti-LOS antibodies in 26 of 30 mice (87%). IgG anti-LOS antibody elicited by Octa-MAP1 immunization possessed dose-responsive direct complement (C)-dependent bactericidal activity against gonococcal strains that expressed the 2C7 epitope. These data indicate that a peptide can mimic an oligosaccharide epitope and may form the basis for the development of a vaccine candidate for human immunization against N. gonorrhoeae.

Intranasal immunization with outer membrane protein P6 and cholera toxin induces specific sinus mucosal immunity and enhances sinus clearance of nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is one of the leading pathogens in sinusitis. One of the outer membrane proteins of NTHi, P6, is a common antigen to all strains and is an attractive candidate for a subunit bacterial vaccine. In this study, we characterized normal sinus mucosa (SM) and investigated the potential of intranasal immunization with P6 and cholera toxin (CT) for induction of mucosal protective immunity against NTHi in the maxillary sinuses of rats. Intranasal immunization induced P6-specific sinus mucosal and systemic immunological responses, mainly of the IgA and IgG isotype. The protective effect of intranasal immunization was demonstrated by enhancement of sinus clearance of NTHi. The present study showed that unilateral intranasal immunization has a capacity to induce protective immunity against NTHi in the bilateral maxillary sinuses. Systemic administration of the vaccine did not affect sinus clearance of NTHi. These findings suggest that a nasal vaccine might be useful for preventing sinusitis.

Human antibodies specific for the high-molecular-weight adhesion proteins of nontypeable Haemophilus influenzae mediate opsonophagocytic activity

The HMW1- and HMW2-like adhesion proteins of nontypeable Haemophilus influenzae are expressed by 75% of these strains, and antibodies directed against these proteins are protective in animal models of infection. The purpose of the present study was to define the functional activity of human antibodies specific for these proteins in an in vitro complement-dependent opsonophagocytic assay. Human promyelocytic cell line HL-60 served as the source of phagocytic cells, and a commercial preparation of intravenous immunoglobulin (IVIG) served as the source of human antibodies. High-molecular-weight (HMW) proteins were purified from four prototype nontypeable H. influenzae strains and used to prepare solid-phase affinity columns. IVIG was adsorbed on each column to remove strain-specific anti-HMW antibodies and to allow recovery of affinity-purified anti-HMW antibody fractions. Unadsorbed IVIG killed each of the prototype strains at titers of 1:80 to 1:320. HMW-adsorbed sera demonstrated fourfold decreases in opsonophagocytic titer against the homologous strains compared to unadsorbed IVIG. Affinity-purified anti-HMW antibody preparations demonstrated opsonophagocytic titers of 1:20 to 1:80 against the respective homologous strains and opsonophagocytic titers as high as 1:80 against heterologous strains. None of the affinity-purified anti-HMW antibody preparations was opsonophagocytic for a representative nontypeable H. influenzae strain that did not express HMW1- or HMW2-like proteins. These data demonstrate that human antibodies specific for the HMW1/HMW2-like adhesion proteins of nontypeable H. influenzae are opsonophagocytic and that such antibodies recognize epitopes shared by the HMW proteins of unrelated nontypeable H. influenzae strains. These results argue for continued investigation of the HMW1/HMW2-like proteins as potential vaccine candidates for prevention of disease due to nontypeable H. influenzae.

The Lip lipoprotein from Neisseria gonorrhoeae stimulates cytokine release and NF-kappaB activation in epithelial cells in a Toll-like receptor 2-dependent manner

The human pathogen Neisseria gonorrhoeae produces an array of diseases ranging from urethritis to disseminated gonococcal infections. Early events in the establishment of infection involve interactions between N. gonorrhoeae and the mucosal epithelium, which leads to the local release of inflammatory mediators. Because of this, it is important to identify the bacterial virulence factors and host cell components that contribute to inflammation. Using a series of column chromatography steps, we purified a lipoprotein from N. gonorrhoeae strain F62 called Lip. This outer membrane antigen expresses a conserved epitope known as H.8, which is common to all pathogenic Neisseria species. We found the purified preparation of Lip to be a potent inflammatory mediator capable of inducing the release of the chemokine interleukin (IL)-8 and the cytokine IL-6 by immortalized human endocervical epithelial cells and the production of IL-8 and the activation of the transcription factor NF-kappaB by human embryonic kidney 293 (HEK) cells transfected with toll-like receptor (TLR) 2. Upon removal of Lip by immunoprecipitation, the ability of the H.8/Lip preparation to stimulate NF-kappaB activation was abolished. In addition to TLR2, the activation of NF-kappaB by H.8/Lip in HEK cells was enhanced upon coexpression of TLR1 but not TLR6. These observations provide evidence that Lip is capable of inducing the release of inflammatory mediators from epithelial cells in a TLR2-dependent manner.

Single cell analysis of adenoid CD5+ B cells and their protective contributions to nasopharyngeal immunity

OBJECTIVES

CD5+ B cells are phenotypically and functionally distinct from the conventional (CD5-) B cells, and the function of CD5+ B cells in the upper respiratory tract remains unknown. A previous study showed that immunoglobulin A-producing cells in the adenoid play a protective role in the nasopharynx. In the present study, the contribution of adenoid CD5+ B cells to nasopharyngeal immunity at the single cell level was investigated.

STUDY DESIGN

In vitro laboratory study.

METHODS

Mononuclear cells were isolated from adenoids of children aged 1 to 12 years, and the frequency of CD5+ B cells was determined by flow cytometry. The numbers of cells producing immunoglobulin M, immunoglobulin G, and immunoglobulin A in sorted adenoid CD5+ B cells were determined by enzyme-linked immunospot assay. Further, to characterize adenoid CD5+ B cells, the expression of various surface molecules was analyzed by flow cytometry.

RESULTS

The results showed that adenoids of young children contain a relatively large number of CD5+ B cells, which have a greater capacity for antibody production than do CD5- B cells. CD5+ B cells also differed from CD5- B cells in the expression of interleukin receptors Il-4R, IL-5R, and IL-10R as well as CD27, B7-1, B7-2, Fas, and Bcl-2.

CONCLUSIONS

These findings suggest that adenoid CD5+ B cells contribute to protective immunity by forming a first line of defense in the upper respiratory tract of young children and that they are probably regulated in a manner that differs from that of CD5- B cells.

Variability of outer membrane protein P1 and its evaluation as a vaccine candidate against experimental otitis media due to nontypeable Haemophilus influenzae: an unambiguous, multifaceted approach

Candidate vaccine antigens for preventing otitis media caused by nontypeable Haemophilus influenzae (NTHI) should possess one or more conserved epitopes. We sought to evaluate the candidacy of P1, a surface-expressed outer membrane protein knowing that this antigen is subject to diversifying selection. Therefore, we selected NTHI strains from among >500 phylogenically variant isolates representative of the diversity found in natural populations of H. influenzae. Twenty-three variants of P1 (</=95% similarity) were identified among 42 strains. When chinchillas were immunized with recombinant P1 (rP1) obtained from one of these isolates (BCH-3), all animals developed antibodies specific for rP1. Immunized animals were protected against disease when challenged with BCH-3, but not with an ompP1 mutant of BCH-3 or a strain (BCH-2) possessing a heterologous P1 (91% identity). We conclude that (i) while P1 induces protection against NTHI-mediated otitis media, development of a polyvalent vaccine reflecting the variability of P1 would be necessary to construct an efficacious vaccine and (ii) use of a phylogenically characterized collection of representative isolates in concert with gene sequencing, cloning, gene inactivation, and animal testing offers an efficient, rational, and rigorous strategy for evaluating the potential problems associated with variability of vaccine targets and specificity of related immune responses.

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.

Outer membrane proteins as a carrier for detoxified lipooligosaccharide conjugate vaccines for nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is a common cause of otitis media and respiratory tract infections. Outer membrane proteins (OMP) and lipooligosaccharide (LOS) are major surface antigens of NTHi and potential vaccine candidates. De-O-acylated LOS (dLOS) or oligosaccharide (OS) was coupled to total OMP to form dLOS-OMP and OS-OMP conjugates, while a dLOS-tetanus toxoid (TT) was synthesized for comparison. These conjugates were evaluated in mice and rabbits for immunogenicity. dLOS-OMP elicited a better boostable antibody response against LOS than did dLOS-TT, while OS-OMP was not immunogenic. Formulation of the conjugates with Ribi adjuvant significantly enhanced the immunogenicity of dLOS-OMP and dLOS-TT but not that of OS-OMP. In addition, rabbit antisera elicited by dLOS-OMP but not dLOS-TT (or OMP alone) demonstrated bactericidal activity against 40% of the NTHi strains tested. These results indicate that dLOS is a better derivative of LOS than OS and that OMP is a good carrier for NTHi LOS-based conjugate vaccines.

Enhancement of nasal clearance of nontypeable Haemophilus influenzae by oral immunization with outer membrane proteins

BALB/c mice were orally immunized with liposomes containing outer membrane proteins (OMPs) isolated from nontypeable Haemophilus influenzae (NTHi) and GM-53 as an adjuvant daily for 14 days. Anti-OMP IgA antibody titers in nasal wash, saliva, and fecal extract were significantly increased after the immunization. Although anti-OMP IgM and IgG antibodies were detected in serum, serum IgA antibodies specific to OMPs were not found. Enzyme-linked immunospot assay showed an increased number of OMP-specific IgA-secreting cells in nasal passages, intestinal lamina propria lymphocytes, and the spleen. Following oral immunization, a suspension of live NTHi was injected into the nose; nasal washes were collected 12 h after the inoculation. The number of NTHi in nasal washes was significantly reduced in mice immunized with liposomes containing OMPs and GM-53 compared to that in mice immunized with liposomes containing GM-53 alone. There was a significant negative correlation between the number of NTHi and anti-OMP IgA antibody titers in nasal washes. These findings suggest that antigen-specific IgA responses in the nose can be induced by oral immunization with OMPs and might be associated with the ability to clear NTHi from the nose.

Nontypeable Haemophilus influenzae: pathogenesis and prevention

In this paper, we describe the ability of nontypeable Haemophilus influenzae (NTHi) to coexist with the human host and the devastating results associated with disruption of the delicate state of balanced pathogenesis, resulting in both acute and chronic respiratory tract infections. It has been seen that the strains of NTHi causing disease show a marked genetic and phenotypic diversity but that changes in the lipooligosaccharide (LOS) and protein size and antigenicity in chronically infected individuals indicate that individual strains of NTHi can remain and adapt themselves to avoid expulsion from their infective niche. The lack of reliance of NTHi on a single mechanism of attachment and its ability to interact with the host with rapid responses to its environment confirmed the success of this organism as both a colonizer and a pathogen. In vitro experiments on cell and organ cultures, combined with otitis media and pulmonary models in chinchillas, rats, and mice, have allowed investigations into individual interactions between NTHi and the mammalian host. The host-organism interaction appears to be a two-way process, with NTHi using cell surface structures to directly interact with the mammalian host and using secreted proteins and LOS to change the mammalian host in order to pave the way for colonization and invasion. Many experiments have also noted that immune system evasion through antigenic variation, secretion of enzymes and epithelial cell invasion allowed NTHi to survive for longer periods despite a specific immune response being mounted to infection. Several outer membrane proteins and LOS derivatives are discussed in relation to their efficacy in preventing pulmonary infections and otitis media in animals. General host responses with respect to age, genetic makeup, and vaccine delivery routes are considered, and a mucosal vaccine strategy is suggested.

Nasopharyngeal colonization with nontypeable Haemophilus influenzae in chinchillas

Colonization of the nasopharynx by a middle ear pathogen is the first step in the development of otitis media in humans. The establishment of an animal model of nasopharyngeal colonization would therefore be of great utility in assessing the potential protective ability of candidate vaccine antigens (especially adhesins) against otitis media. A chinchilla nasopharyngeal colonization model for nontypeable Haemophilus influenzae (NTHI) was developed with antibiotic-resistant strains. This model does not require coinfection with a virus. There was no significant difference in the efficiency of NTHI colonization between adult (1- to 2-year-old) and young (2- to 3-month-old) animals. However, the incidence of middle ear infection following nasopharyngeal colonization was significantly higher in young animals (83 to 89%) than in adult chinchillas (10 to 30%). Chinchillas that had recovered either from a previous middle ear infection caused by NTHI or from an infection by intranasal inoculation with NTHI were completely protected against nasopharyngeal colonization with a homologous strain and were found to be the best positive controls in protection studies. Systemic immunization of chinchillas with inactivated whole-cell preparations significantly protected animals not only against homologous NTHI colonization but also partially against heterologous NTHI infection. In all protected animals, significant serum anti-P6 and anti-HMW antibody responses were observed. The outer membrane P6 and high-molecular-weight (HMW) proteins appear to be promising candidate vaccine antigens to prevent nasopharyngeal colonization and middle ear infection caused by NTHI.

The acylated form of protein D of Haemophilus influenzae is more immunogenic than the nonacylated form and elicits an adjuvant effect when it is used as a carrier conjugated to polyribosyl ribitol phosphate

The nonacylated form of protein D (PDm) of Haemophilus influenzae has been shown to induce the production of antibodies that are bactericidal to homologous and heterologous nontypeable H. influenzae (NTHi) strains. In this study, immunization of rats with lipoprotein D (LPD) induced higher levels of anti-protein D immunoglobulin G and A serum antibodies than immunization with PDm, and the bactericidal activities of sera from LPD-immunized rats were greater than those of sera from PDm-immunized rats. Immunization with LPD or PDm did not prevent the development of acute otitis media (AOM) when rats were challenged with 10(4) CFU of an NTHi strain. However, on the eighth day of bacterial challenge, 50% (5 of 10) of LPD-immunized rats had recovered from otitis media and 30% (3 of 10) had negative middle ear cultures, whereas only 30% (3 of 10) of PDm-immunized rats had recovered, though none was culture positive. Immunization with an inactivated homologous bacterial strain elicited 70% protection (i.e., 7 of 10 rats) in the rat otitis media model. LPD and PDm were also conjugated to the H. influenzae type b (Hib) capsular polysaccharide, polyribosyl ribitol phosphate (PRP), to test protein D-conjugated PRP vaccine's potential for protection against Hib infection. When two LPD-conjugated and two PDm-conjugated PRP vaccines, each containing a different protein concentration, and a tetanus toxoid-conjugated vaccine (ACT-HIB) were tested in the experimental model of rat otitis induced with a Hib strain (Minn A), both of the LPD-conjugated and one of the PDm-conjugated vaccines induced significant protection from AOM, the level of protection being highest in animals given the vaccine with the highest LPD content. Sera from these rats also manifested the highest anti-PRP and anti-LPD antibody levels and the highest bactericidal activities against a Hib strain and an NTHi strain.

Immunoglobulin G Subclass Response to Major outer Membrane Proteins of Nontypable Haemophilus Influenzae in Children with Acute Otitis Media

Children with acute otitis media as the result of nontypable Haemophilus influenzae often develop serum bactericidal and/or opsonic IgG antibodies to this organism during convalescence. Outer membrane proteins appear to be the principal targets for such antibodies. In this study we characterized the IgG subclass responses to major outer membrane proteins of nontypable H. influenzae in otitis-prone children in whom this organism had colonized. Three of the major outer membrane proteins (P2, P5, and P6) were isolated from the homologous nontypable H. influenzae strain recovered from the middle ear at the time of acute infection. Sera were obtained during the acute phase and at 1 and 6 months thereafter. The outer membrane proteins, which were isolated by preparative sodium dodecylsulfate-polyacrylamide gel electrophoresis, were used as test antigens in a quantitative IgG subclass enzyme immunoassay. The results of this analysis indicate that the temporal characteristics and distribution of IgG subclass antibodies were found to differ for each of the outer membrane proteins. Moreover, substantial variation between patients was observed with respect to both temporal characteristics and subclass distribution of the IgG response to the three outer membrane proteins. Significantly, sera from two of three otitis-prone subjects contained detectable levels of IgG antibody to the conserved P6 outer membrane protein at the time of acute infection, with serum from one subject also containing detectable levels of lgG3 antibody to this same protein. Nevertheless, the organism persisted in the middle ears of these patients. The results of this study indicate that otitis-prone children manifest a highly variable IgG subclass response to both conserved (P6) and variable (P2) outer membrane proteins of nontypable H. influenzae. Further study is required to ascertain whether these IgG subclass antibodies are biologically efficacious and whether otitis-prone children possess the immunologic maturity to respond to nontypable H. influenzae outer membrane protein-based vaccines in a predictable manner.

Effect of amplification of the Cap b locus on complement-mediated bacteriolysis and opsonization of type b Haemophilus influenzae

Amplification of the Cap b locus of Haemophilus influenzae occurs frequently in clinical isolates and has been proposed to be a mechanism by which this organism evades host defense. To determine if amplification of this locus affected complement fixation, in vitro studies to determine complement-mediated bacteriolysis and complement-mediated opsonization of an isogenic set of organisms containing 2, 3, and 4 copies of the Cap b locus were performed. Organisms containing 4 copies of the Cap b locus were significantly more resistant to antibody-dependent, classical complement pathway-directed bacteriolysis than were organisms containing 2 copies. Organisms containing 3 copies of this locus exhibited intermediate susceptibility to lysis. Complement-mediated opsonization of these organisms was assessed by determining the degree of binding of bacteria to murine or human macrophages or to nonphagocytic cells transfected with the genes for human Mac-1, the complement receptor type 3. In all three assay systems, organisms containing 4 copies of the Cap b locus bound less well than did organisms containing 2 copies of this locus. Consistent with their decreased susceptibility to lysis and opsonization, organisms with 4 copies of the Cap b locus fixed less C3 than did organisms containing 2 copies. These data demonstrate that amplification of the Cap b locus is associated with decreased susceptibility to complement-mediated lysis and decreased complement-mediated opsonization and suggest that amplification is used by these pathogens to increase their resistance to complement-dependent host defense mechanisms [correction of mecanisms].

Biological activity of serum antibodies to a nonacylated form of lipoprotein D of Haemophilus influenzae

Protein D, a surface-exposed 42-kDa membrane lipoprotein, is well conserved among both type b and nontypeable Haemophilus influenzae strains, and it is considered a vaccine against H. influenzae infections. Here, we report the large-scale purification of a nonacylated form of protein D (PDm) from the periplasmic space of Escherichia coli overexpressing PDm. Screening of human sera for levels of antibodies to PDm demonstrated that the immunoglobulin G (IgG) antibody level is above background levels in infants less than 6 months of age. Following a drop to background values in the age group 6 months to 1 year, IgG antibody levels start to increase, together with IgA antibody levels, after 1 year of age. The first appearance of serum IgM antibodies is in 6-month- to 1-year-old infants whose IgG antibody levels have dropped to the postnatal background level. Affinity-purified antibodies from humans and from PDm-immunized rats detected epitopes of protein D which are normally exposed on the bacterial surface. Affinity-isolated human anti-PDm antibodies eluted in acidic buffer were not bactericidal against H. influenzae. Loss of bactericidal activity may occur in this buffer, as was demonstrated in pooled human sera with high bactericidal activity after incubation in the same buffer. Hyperimmunization of rats with PDm induced high levels of serum IgG and IgA antibodies against PDm and significant bactericidal activity against homologous and heterologous H. influenzae strains.

Identification of surface-exposed B-cell epitopes on high molecular-weight adhesion proteins of nontypeable Haemophilus influenzae

We previously reported that two surface-exposed high-molecular-weight proteins, HMW1 and HMW2, expressed by a prototypic strain of nontypeable Haemophilus influenzae (NTHI) mediate attachment to human epithelial cells. These proteins are members of a family of highly immunogenic proteins common to most nontypeable Haemophilus strains. We also reported that immunization with an HMW1-HMW2 mixture modified the course of disease in an animal model of otitis media, suggesting the potential usefulness of these proteins as NTHI vaccine components. Identification of surface-accessible B-cell epitopes could be important to efforts to develop recombinant or synthetic peptide vaccines based upon these high-molecular-weight proteins. Thus, the purpose of the present study was to identify surface-accessible epitopes on the HMW1 and HMW2 proteins by using monoclonal antibodies (MAbs) and to determine the prevalence of these epitopes among the high-molecular-weight proteins expressed by heterologous nontypeable Haemophilus strains. MAbs were generated by immunizing mice with high-molecular-weight proteins purified from prototype strains and were screened by immunoelectron microscopy (IEM) for the ability to recognize surface epitopes. Two MAbs, designated AD6 and 10C5, that recognized surface epitopes by IEM were recovered. In order to map the epitopes recognized by these two MAbs, we constructed a set of HMW1 and HMW2 recombinant fusion proteins using the pGEMEX vectors and examined the reactivity of the MAbs with these fusion proteins. MAb AD6 recognized an epitope in both HMW1 and HMW2 which mapped to the last 75 amino acids at the carboxy termini of the two proteins. When examined for reactivity with heterologous strains, MAb AD6 recognized high-molecular-weight proteins in 75% of 125 unrelated nontypeable Haemophilus strains and, in addition, reacted with three of three such strains when examined by IEM. MAb 10C5 recognized an epitope that mapped to a 155-amino-acid segment near the carboxy terminus of HMW1. This epitope was adjacent to but distinct from the AD6 epitope and was absent from HMW2. The 10C5 epitope was expressed by 40% of the AD6 reactive strains. Identification of shared surface-exposed epitopes on the high-molecular-weight adhesion proteins suggests the possibility of developing recombinant or synthetic peptide-based vaccines protective against disease caused by the majority of NTHI strains.

Immunization with high-molecular-weight adhesion proteins of nontypeable Haemophilus influenzae modifies experimental otitis media in chinchillas

Prevention of nontypeable Haemophilus influenzae otitis media by vaccination is an important health care goal. Proteins important in bacterial adherence deserve consideration as potential vaccine candidates. Two colleagues and I previously identified a family of immunogenic high-molecular-weight proteins important in adherence of nontypeable H. influenzae to human epithelial cells (J.W. St. Geme III, S. Falkow, and S.J. Barenkamp, Proc. Natl. Acad. Sci. USA, 90:2875-2879, 1993). In the work described here, I determined whether immunization with two such adherence proteins, HMW1 and HMW2, purified from prototype nontypeable Haemophilus strain 12, would modify the course of experimental otitis media caused by the homologous strain. Chinchillas received three monthly subcutaneous injections with 40 microgram of an HMW1/HMW2 protein mixture in Freud's adjuvant. One month after the last injection, animals were challenged by intrabullar inoculation with 300 CFU of nontypeable H. influenzae 12. Infection developed in five of five control animals versus 5 of 10 immunized animals (P = 0.08, Fisher exact, one-tailed). Among infected animals, bacterial counts in middle ear fluid specimens 7 days postchallenge were significantly greater in control animals than in immunized animals (P = 0.014, Mann-Whitney U test). Serum antibody titers following immunization were comparable in uninfected and infected animals. However, infection in immunized animals was uniformly associated with the appearance of bacteria downregulated in expression of the high-molecular-weight proteins, suggesting bacterial selection in response to immunologic pressure. Although protection following immunization was incomplete, these data suggest that the high-molecular-weight adhesion proteins are potentially important protective antigens which might represent one component of a multicomponent nontypeable Haemophilus vaccine.

Immune selection for antigenic drift of major outer membrane protein P2 of Haemophilus influenzae during persistence in subcutaneous tissue cages in rabbits

During persistence of nonencapsulated Haemophilus influenzae in the respiratory tracts of patients with chronic bronchitis, the major outer membrane proteins (MOMPs) P2 and P5 show antigenic drift. The hypothesis that appearance of antigenic variants is the consequence of antibody-dependent selection was tested in a rabbit model. Persistence of H. influenzae d1 was achieved in subcutaneous tissue cages for up to 948 days. During persistence in the rabbits, similar changes in MOMP P2 of H. influenzae occurred, as observed in isolates from chronic bronchitis patients. In rabbits vaccinated with strain d3 and in nonvaccinated rabbits, antigenic drift occurred later than in rabbits vaccinated with strain d1. High titers of antibodies against H. influenzae were measured in tissue cage fluid and serum. Vaccination of the rabbits with H. influenzae d1 or d3, an antigenic variant of strain d1, resulted neither in eradication of H. influenzae d1 nor in increased antibody titers in serum and tissue cage fluid. The sera of nonvaccinated rabbits during persistence had no strain d1-specific bactericidal activity in the presence of complement. Vaccination with H. influenzae d1 induced serum bactericidal activity against strain d1 in the presence of complement. However, a variant of strain d1 appearing in the tissue cages was not killed by this serum bactericidal activity. We conclude that immunological pressure leads to the selection of MOMP variants of H. influenzae and that these variants escape the antibody-mediated strain-specific bactericidal activity against H. influenzae.

Progress towards a vaccine for nontypable Haemophilus influenzae

Nontypable Haemophilus influenzae is a common cause of human disease and is associated with significant morbidity and considerable societal cost. At present, measures to prevent nontypable H. influenzae disease are limited to prophylactic antibiotics and, on occasion, exogenous antibody preparations. However, because these interventions are often inadequate, there is interest in developing an effective vaccine. Given the marked diversity among epidemiologically unrelated strains and the frequent strain specificity of the immune response to infection, efforts have focused on identifying bacterial antigens that are highly conserved and capable of stimulating protective antibody. With the recent identification of several such antigens, attention must now turn toward selecting the appropriate combination of these molecules and determining the optimal strategy for their presentation to the immune system. The ultimate goal is to induce broad-based and long-lasting protection.

Mapping of a surface-exposed, conformational epitope of the P6 protein of Haemophilus influenzae

P6 is an outer membrane protein of Haemophilus influenzae that is antigenically conserved and considered a candidate component of future H. influenzae vaccines. P6 contains a surface-exposed epitope recognized by monoclonal antibody (MAb) 3B9. This epitope has been shown to be distinct from that recognized by the P6-specific MAbs 7F3 and 4G4 in a competitive inhibition enzyme-linked immunosorbent assay (ELISA). MAb 3B9 did not bind to synthetic P6-specific sequential and overlapping hexameric peptides. Five peptides made to correspond to P6 sequences with high probabilities of surface exposure did not inhibit binding of MAb 3B9 to P6. An antiserum to one of the peptides, designated SP66, inhibited binding of MAb 3B9 to P6. A rabbit antiserum to P6 bound to sequential hexameric peptides, Gly-87AsnThrAspGluArgGlyThr-94, which were in the SP66 region of P6. This antiserum inhibited the binding of P6 to MAb 3B9 in a competitive inhibition ELISA. P6 mutations with His and Ala substitutions at residues Thr-88 and Asn-89 still bound MAb 3B9. MAb 3B9 reacted with Escherichia coli OmpA and Salmonella typhimurium OmpA. Sequence comparisons of P6 with these proteins indicated that the residue in the SP66 region responsible for binding is either Gly-87, Asp-90, or Gly-93. Mercaptoethanol reduction abolished MAb 3B9 binding to E. coli OmpA and S. typhimurium OmpA. In these proteins, immediately downstream of the second cysteine, there is an ArgArg dipeptide which is identical to and aligns with Arg-147Arg-148 in P6. This dipeptide has a high probability of surface exposure in P6. Mutagenesis of the Arg-147Arg-148 to an AlaAla dipeptide in P6 abolished binding of MAb 3B9, demonstrating that it was either a portion of the epitope or important in the protein folding necessary for expression of this epitope. This study demonstrates that MAb 3B9 recognizes a conserved conformational determinant on the surface of H. influenzae that is composed of two discontinuous regions of P6.

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

Cellular immunity to nontypeable Haemophilus influenzae in a population of 10 healthy, immune adults was determined by measuring lymphocyte blast transformation and antibody secretion in response to the P6 outer membrane protein. P6 (200 microliters/ml) induced lymphocyte blast transformation that peaked on day 10 of incubation. The peak induction of antibody-secreting cells occurred on day 8 of incubation. In comparison with the response to tetanus toxoid stimulation, the peak lymphocyte blast transformation response to P6 was reduced (mean counts per minute +/- standard error of the mean [SEM], 3,457 +/- 503 versus 9,414 +/- 1,464; P = 0.0051) and delayed (mean days +/- SEM, 10.3 +/- 0.4 versus 8.4 +/- 0.5; P = 0.0169); however, P6 was a better stimulus of antibody secretion from lymphocytes, particularly antibody of the immunoglobulin M (IgM) class (mean peak numbers of antibody-secreting cells per 10(5) peripheral blood mononuclear cells +/- SEM: IgG, 85 +/- 29 versus 42 +/- 16 [P = 0.0469]; IgM, 81 +/- 20 versus 25 +/- 7 [P = 0.0125]; IgA, 24 +/- 8 versus 16 +/- 6 [P = 0.0526]). Thus, lymphocytes from immune individuals recognize P6 of nontypeable H. influenzae as an immunogen. These data provide a basis for future studies with otitis-prone children who fail to develop a normal antibody response to P6 antigen (N. Yamanaka and H. Faden, J. Pediatr. 122:212-218, 1993).

Protection against non-typable Haemophilus influenzae following sensitization of gut associated lymphoid tissue: role of specific antibody and phagocytes

Rats intestinally immunized with whole killed non-typable Haemophilus influenzae clear this organism from the lungs faster than non-immunized rats. This study investigated the role of antibody and phagocytes in the clearance mechanism. First, dose-response experiments demonstrated that while lowering the dose of non-typable H. influenzae reduced the level of detectable specific antibody in bronchial washings, the ability to accelerate bacterial clearance persisted to much lower doses. Second, specificity experiments showed that intestinal immunization with non-typable H. influenzae cross-protected against Pseudomonas aeruginosa, even though antibodies were not absorbed out of serum by incubation with P. aeruginosa. Third, serum antibody was shown to be bactericidal for non-typable H. influenzae in the presence of complement (P < 0.05), while bronchial washings antibody was not. The bactericidal effect of the serum was abrogated by the addition of bronchial washings. Fourth, an ELISA quenching assay demonstrated that neutrophils from intestinally immunized rats were able to phagocytose more bacteria in a given time period (P < 0.05) than unimmunized rats and rats immunized by other routes. In the fifth experiment, the chemotactic response of neutrophils to casein was shown to be significantly depressed by the addition of bronchial washings obtained from immunized rats (P < 0.01). It is proposed that specific antibody in bronchial washings does not have a direct role in opsonizing bacteria for killing or phagocytosis, but instead has an anti-inflammatory effect. Non-specific effectors such as neutrophils driven by specific immune cells are a likely means of clearance of bacteria following intestinal immunization and acute challenge.

Mapping of bactericidal epitopes on the P2 porin protein of nontypeable Haemophilus influenzae

The P2 porin protein is the major outer membrane protein of nontypeable Haemophilus influenzae and is a potential target of a protective immune response. Nine monoclonal antibodies (MAbs) to P2 were developed by immunizing mice with nontypeable H. influenzae whole organisms. Each MAb reacted exclusively with the homologous strain in a whole-cell immunodot assay demonstrating exquisite strain specificity. All nine MAbs recognized abundantly expressed surface-exposed epitopes on the intact bacterium by immunofluorescence and immunoelectron microscopy. Each MAb was bactericidal to the homologous strain in an in vitro complement-mediated killing assay. Immunoblot assay of cyanogen bromide cleavage products of purified P2 indicated that MAb 5F2 recognized the 10-kDa fragment, and the other eight MAbs recognized the 32-kDa fragment. Competitive ELISAs confirmed that 5F2 recognized an epitope that is different from the other eight MAbs. To further localize epitopes, MAbs 5F2 and 6G3 were studied in protein footprinting by using reversed-phase high-performance liquid chromatography. Three potential epitope-containing peptides which were reactive in an enzyme-linked immunosorbent assay with both 5F2 and 6G3 were isolated. These peptides were identified by N-terminal amino acid sequence and localized to loops 5 and 8 of the proposed model for P2. Fusion proteins consisting of glutathione S-transferase fused with variable-length peptides from loops 5 and 8 were expressed in the pGEX-2T vector. Immunoblot assay of fusion peptides of loops 5 and 8 confirmed that 5F2 recognized an epitope within residues 338 to 354 of loop 8; 6G3 and the remaining MAbs recognized an epitope within residues 213 to 229 of loop 5. These studies indicate that nontypeable H. influenzae contains bactericidal epitopes which have been mapped to two different surface-exposed loops of the P2 molecule. These potentially protective epitopes are strain specific and abundantly expressed on the surface of the intact bacterium.

Opsonic antibodies to outer membrane protein P2 of nonencapsulated Haemophilus influenza are strain specific

The ability of monoclonal antibodies (MAbs) specific for variable and conserved epitopes of outer membrane protein (OMP) P2 (b,c) of nonencapsulated Haemophilus influenza to promote opsonophagocytosis of this bacterium by human polymorphonuclear leucocytes (PMNs) was determined by flow cytometry. MAbs rendering PMNs fluorescent because of association with fluorescein isothiocyanate-labelled bacteria were defined as stimulating opsonophagocytosis. Opsonophagocytosis was dependent on the presence of both antibodies and complement. Of the 14 MAbs directed to the variable parts of OMP P2 (L. van Alphen, P. Eijk, L. Geelen-van den Broek, and J. Dankert, Infect. Immun. 59:247-252, 1991), 9 stimulated opsonophagocytosis. Four of the five nonopsonophagocytic MAbs that were immunoglobulin G1 were unable to cause complement activation. The MAbs promoting opsonophagocytosis included MAbs specific for one or more OMP P2 antigenic variants of H. influenzae strains isolated from patients with chronic bronchitis during persistent infection. MAbs cross-reacting in enzyme-linked immunosorbent assays with nonrelated H. influenzae did not promote opsonophagocytosis of strains from other patients. Opsonophagocytosis was not observed in the presence of three MAbs reacting with OMP P2 epitopes common in H. influenzae. These results indicate that OMP P2-dependent opsonophagocytosis of nonencapsulated H. influenzae is strictly strain specific.

Antigenic drift of non-encapsulated Haemophilus influenzae major outer membrane protein P2 in patients with chronic bronchitis is caused by point mutations

The sequence of the gene encoding major outer membrane protein (MOMP) P2 of antigenic variants of non-encapsulated Haemophilus influenzae isolated from persistently infected chronic bronchitis patients was analysed. Antigenic drift was shown to result from single base changes in the P2 gene, all generating amino acid changes in the surface-exposed loops of MOMP P2, predominantly in loop 6. Similar single base changes were observed in H. influenzae persistently present in a subcutaneous cage implanted in rabbits, as well as in a spontaneous H. influenzae mutant that had survived MOMP P2 specific monoclonal-antibody-dependent bactericidal killing in vitro. We hypothesize that accumulation of point mutations under the selection pressure of immunity is a mechanism of antigenic drift of a surface-exposed protein during persistent H. influenzae infection.

Antibody response to outer membrane protein of nontypeable Haemophilus influenzae in otitis-prone children

One of the major outer membrane proteins of nontypeable Haemophilus influenzae, P6, is highly conserved among strains, serves as a target for bactericidal antibody, and has been proposed as a possible vaccine candidate. The serum antibody response to P6 was studied in otitis-prone and normal children by an enzyme-linked immunosorbent assay. Of 20 otitis-prone children, 12 (60%) had a serum IgG antibody response to P6 after otitis media; however, the mean acute antibody level for the group, 4.6 micrograms/ml, was not significantly different from the convalescent level, 5.4 micrograms/ml. Anti-P6 antibody levels were also measured longitudinally for 10 to 25 months in 30 otitis-prone and 13 healthy children. Antibody levels increased sevenfold in the normal group compared with less than three-fold for the otitis-prone group and were significantly higher in the normal children after the age of 18 months (p < 0.05). Finally, otitis-prone children who had two or more episodes of otitis media with nontypeable H. influenzae did not have an anamnestic antibody response to P6. The failure to recognize P6 as a specific immunogen may account for recurrent infections. Moreover, the data suggest that otitis-prone children may not respond adequately to a vaccine containing P6.

Cloning, expression, and DNA sequence analysis of genes encoding nontypeable Haemophilus influenzae high-molecular-weight surface-exposed proteins related to filamentous hemagglutinin of Bordetella pertussis

A group of high-molecular-weight surface-exposed proteins of nontypeable Haemophilus influenzae are major targets of human serum antibody (S. J. Barenkamp and F. F. Bodor, Pediatr. Infect. Dis. J. 9:333-337, 1990). To further characterize these proteins, we cloned and sequenced genes encoding two related high-molecular-weight proteins from a prototype nontypeable Haemophilus strain. The gene encoding a 120-kDa Haemophilus protein consisted of a 4.4-kbp open reading frame, and the gene encoding a 125-kDa protein consisted of a 4.6-kbp open reading frame. The first 1,259 bp of the two genes were identical. Thereafter, the sequences began to diverge, but overall they were 80% identical, and the derived amino acid sequences showed 70% identity. A protein sequence homology search demonstrated similarity between the derived amino acid sequences of both cloned genes and the derived amino acid sequence of the gene encoding filamentous hemagglutinin, a surface protein produced by the gram-negative pathogen Bordetella pertussis. Antiserum raised against a recombinant protein encoded by the 4.6-kbp open reading frame recognized both the 120- and the 125-kDa proteins in the prototype strain as well as antigenically related high-molecular-weight proteins in 75% of a collection of 125 epidemiologically unrelated nontypeable H. influenzae strains. The antiserum directed against the recombinant protein also recognized purified filamentous hemagglutinin. A murine monoclonal antibody to filamentous hemagglutinin recognized both the 120-kDa and the 125-kDa protein in the prototype strain as well as proteins identical to those recognized by the recombinant-protein antiserum in 35% of the nontypeable H. influenzae strain collection. Thus, we have identified and partially characterized a group of highly immunogenic surface-exposed proteins of nontypeable H. influenzae which are related to the filamentous hemagglutinin of B. pertussis.

Complement component 3 binding to Haemophilus influenzae type b in the presence of anticapsular and anti-outer membrane antibodies

Antibodies directed against the capsular polysaccharide (polyribosyl ribitol phosphate [PRP]) or the outer membrane proteins (OMP) of Haemophilus influenzae type b (Hib) promote bactericidal activity, complement 3 (C3) binding, and ingestion by phagocytic cells. To assess the relative contribution of anti-OMP to host defense against Hib, we compared the opsonic activities of anti-PRP and anti-OMP as reflected by the amounts of C3 bound to the bacterial surface. Immunoglobulin G (IgG) fractions containing either anti-PRP or anti-OMP were incubated with Hib in the presence of a C5-deficient complement source. C3, total IgG, and IgG subclasses bound to the bacteria were quantified by enzyme-linked immunosorbent assay. The maximum amount of C3 which could be bound to Hib was greater in the presence of anti-PRP than in the presence of anti-OMP. Also, except at low IgG concentrations, the rate of increase in bound C3 as a function of increasing IgG concentration was greater for anti-PRP than for anti-OMP. Hib-bound anti-OMP consisted primarily of IgG1 and IgG3, whereas bound anti-PRP was primarily IgG1 and IgG2. Thus, the potential for C3 binding to Hib is greater in the presence of anti-PRP than in the presence of anti-OMP, probably because of the larger number of binding sites available to the former. Nonetheless, OMP appear to provide important targets for opsonic antibody and would be logical components of a PRP-conjugate vaccine or may be efficacious as vaccines against nontypeable H. influenzae.

IgG antibody response of localized juvenile periodontitis patients to the 29 kilodalton outer membrane protein of Actinobacillus actinomycetemcomitans

Levels of serum IgG antibody to the 29 kilodalton outer membrane protein of A. actinomycetemcomitans Y4 in sera of periodontally healthy subjects and localized juvenile periodontitis patients were determined using an enzyme-linked immunosorbent assay (ELISA). The 29 kDa protein was isolated by solubilization of an octylglucoside-NaCl insoluble fraction by incubation at ambient temperature in 20 mM sodium phosphate, pH 7.5, containing 1% sodium dodecyl sulfate. The isolated protein migrated on SDS-polyacrylamide gels with an apparent molecular mass of 29 kDa following incubation in sample buffer at ambient temperature. However, the protein migrated with an apparent molecular mass of 34 kDa following incubation in sample buffer at 100 degrees C for 10 minutes. Geometric mean IgG antibody titers to the 29 kDa protein were significantly higher in sera from LJP subjects than in sera obtained from periodontally healthy subjects. Twenty-two of 35 LJP sera (63%) had antibody titers greater than 2 standard deviations from the mean titer of the periodontally healthy group. Among LJP subjects, elevated antibody titers to the 29 kDa protein were found primarily in subjects greater than or equal to 18 years of age, with the highest titers seen in patients 18 to 21 years of age. The results of this study indicate that the humoral response of LJP subjects to A. actinomycetemcomitans includes the production of IgG antibodies which recognize the major outer membrane proteins of this organism.

Otitis media in children: local immune response to nontypeable Haemophilus influenzae

Twenty children experienced 30 episodes of otitis media with effusion due to nontypeable (NT) Haemophilus influenzae in the first 2 years of life. The local and systemic immune responses to homologous strains of NT H. influenzae were determined by an immunodot assay. Strain-specific immunoglobulin G (IgG) antibody predominated in the middle ear fluid (MEF). It was detected in 91% of the children, compared with IgM in 48% (P less than 0.005), IgA in 52% (P less than 0.005), and secretory IgA in 18% (P less than 0.005). The titer (log2) of NT H. influenzae-specific IgG antibody (mean +/- standard error, 8.2 +/- 0.1) exceeded the titers of IgM (3.4 +/- 0.1), IgA (3.7 +/- 0.1), and secretory IgA (1.2 +/- 0.3). NT H. influenzae-specific antibody was detected exclusively in MEFs of individuals who possessed homologous serum antibody. Although antibody titers in MEF declined over time, serum antibody titers remained stable. These data suggest that immunity to NT H. influenzae in the middle ear, in part, reflects systemic immunity. Whereas local antibody disappears after resolution of the infection, systemic antibody persists.

Immunological responsiveness of chinchillas to outer membrane and isolated fimbrial proteins of nontypeable Haemophilus influenzae

Thin, nonhemagglutinating fimbriae have been demonstrated on 100% of the clinical isolates of nontypeable Haemophilus influenzae recovered from children with chronic otitis media tested in this laboratory (L. O. Bakaletz, B.M. Tallan, T.M. Hoepf, T.F. DeMaria, H.G. Birck, and D.J. Lim, Infect. Immun. 56:331-335, 1988). Chinchillas with induced otitis media responded to this surface-located antigen of both the infecting and a heterologous strain. Antibodies were found in both serum and middle ear fluids.

Isolation of the outer membrane of Branhamella catarrhalis

The emergence of Branhamella catarrhalis as an important human pathogen has stimulated interest in investigations of the outer membrane (OM) of the bacterium. In this study, the OM of B. catarrhalis was isolated and partially characterized. Radiolabelled cells were lysed and fractionated by isopycnic centrifugation in a continuous sucrose gradient. Five fractions were identified. Fraction A consisted of OM fragments of varying density. Fractions B and C were OM of a discrete density containing some cytoplasmic membrane. Fraction D was cytoplasmic membrane and Fraction E contained smaller less dense fragments of cytoplasmic membrane. The protein composition of the Branhamella OM is typical for that of Gram-negative bacteria in that approximately 10 to 20 proteins were present with six to eight of these proteins predominating. Having isolated and partially characterized the OM by sucrose density centrifugation, five simpler techniques for isolating OM were employed and the preparations compared to OM isolated on the gradient. Techniques that are based on differential detergent solubility of OM and cytoplasmic membrane were ineffective in isolating OM of B. catarrhalis. By contrast, techniques that involved collection of OM vesicles were successful in isolating OM of B. catarrhalis. Collection of vesicles from broth culture supernatants and EDTA-heat-induced vesicles were identified as convenient and reliable methods for isolating OM. Isolating and partially characterizing the OM of B. catarrhalis represents an initial step in a systematic study of outer membrane antigens of the bacterium.

Nearest neighbor analysis of outer membrane proteins of nontypeable Haemophilus influenzae

The arrangement of outer membrane proteins on the surface of nontypeable Haemophilus influenzae was investigated with cleavable and noncleavable bis-imidate cross-linking agents. Whole organisms were subjected to cross-linking agents, and oligomers of proteins were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two-dimensional gel electrophoresis, and immunoblot assay, using monoclonal antibodies to outer membrane proteins. The major outer membrane protein (P2) formed dimers and trimers detected by all three methods. Oligomers of other outer membrane proteins were not detected. These data indicate that P2 exists as a trimer on the outer membrane and suggest that other outer membrane proteins exist as monomers on the outer membrane.

Human bactericidal antibody response to outer membrane protein P2 of nontypeable Haemophilus influenzae

The human bactericidal antibody response to the major outer membrane protein, P2, of nontypeable Haemophilus influenzae was studied. P2 was isolated from two strains of nontypeable H. influenzae and coupled to affinity columns. Pooled normal human serum was subjected to affinity chromatography with the P2 columns and a control column. Reducing the titer of antibody to P2 resulted in reduced bactericidal activity of that serum for the organism. Immunopurified antibody to P2 from human serum was bactericidal for the homologous strain. The extent to which these bactericidal determinants on P2 are conserved among strains was investigated. Immunopurified antibodies to P2 of two epidemiologically unrelated isolates were bactericidal for four of six strains tested. We conclude that P2 is a target for human bactericidal antibody and that some of these determinants that are recognized by human bactericidal antibody are conserved among strains of nontypeable H. influenzae.

Purification and analysis with monoclonal antibodies of P2, the major outer membrane protein of nontypable Haemophilus influenzae

The protein P2 comprises a large proportion of the outer membrane of nontypable Haemophilus influenzae and functions as a porin. In view of the importance of the protein as a surface antigen, the present study was designed to purify and analyze P2 with particular emphasis on detection of antigenic determinants expressed on the bacterial surface and identification of bactericidal targets on P2. The P2 protein was purified by using detergent solubility, anion-exchange chromatography, and gel-filtration chromatography sequentially. Two monoclonal antibodies to P2 were developed. One antibody (2E6) recognized a determinant expressed on the bacterial surface, whereas the other antibody (3F3) recognized an internal epitope. The surface-exposed 2E6 determinant was present on 12% of strains from a nationwide collection. P2 is a bactericidal target for antibody 2E6. Cyanogen bromide cleavage of P2 resulted in two fragments, as in type b strains. Both monoclonal antibodies recognized epitopes on the larger fragment. These observations have potentially important implications regarding the development of vaccines to prevent H. influenzae infections and the development of a serotyping system for epidemiologic studies.

Immune enhancement of pulmonary clearance of nontypable Haemophilus influenzae

BALB/c mice systemically immunized by intraperitoneal injection with whole, viable cells of two different strains of nontypable Haemophilus influenzae (NTHI) exhibited a markedly enhanced ability to clear the homologous strain of NTHI from the lower respiratory tract. Immunization did not influence the number of phagocytic cells recovered by bronchoalveolar lavage from mice before or after intrapulmonary challenge with NTHI. Immunization also induced the synthesis of relatively large quantities of NTHI-directed antibodies which were detectable in both the bloodstream and the alveolar spaces of the lung. Radioimmunoprecipitation and Western blot (immunoblot) analyses indicated that these antibodies were directed against both the proteins and lipooligosaccharide (LOS) in the NTHI outer membrane. Bactericidal and opsonophagocytic assays determined that the NTHI-directed antibodies in the serum were functional and able to kill or opsonize the homologous NTHI strain. Mice immunized with an NTHI major outer membrane protein-LOS complex also had an increased ability to effect pulmonary clearance of NTHI. Serum and bronchoalveolar lavage fluid collected from these animals immunized with the outer membrane protein-LOS complex contained relatively high levels of antibodies to both of these antigens. The serum from these animals also possessed bactericidal and opsonic activity against the homologous NTHI strain. These results indicate that systemic immunization can enhance the ability of experimental animals to clear NTHI from the lower respiratory tract and suggest that immunoprophylaxis of NTHI pulmonary disease may be feasible.