Antigenic heterogeneity of lipid A of Haemophilus influenzae

The Immunostimulatory Capacity of Nontypeable Haemophilus influenzae Lipooligosaccharide

Background

We have recently found that lipooligosaccharide (LOS) isolated from encapsulated strains of Haemophilus influenzae (H. influenzae) has strong adjuvant, but diminished pro-inflammatory ability as compared to Escherichia coli lipopolysaccharide (LPS). In this study, we aimed to determine the immunostimulatory capacity of nontypeable/ non-encapsulated H. influenzae (NTHi) LOS by comparing the effect of killed bacteria with LOS isolated from the same strain.

Methods

Following stimulation of human monocytic THP-1 cells with killed NTHi strain 375, or with the corresponding amount of LOS, we studied the protein and gene expression of immunostimulatory and antigen-presenting molecules, cytokines, and innate immune receptors.

Results

Stimulation with LOS resulted in lower expression of adhesion (CD54, CD58) as well as costimulatory molecules (CD40, CD86), but in higher expression of antigen-presenting molecules (HLA-DR and HLA-ABC) compared to killed NTHi, whereas killed bacteria induced higher release of both TNF-α and IL-10. The results indicate that while LOS of NTHi has decreased capacity to induce pro-inflammatory responses compared to E. coli LPS or killed NTHi, this LOS has the potential to facilitate antigen presentation.

Conclusions

Considering the important role of NTHi as a respiratory pathogen, and its currently increasing significance in the etiology of invasive infections, LOS deserves further attention as a vaccine antigen, which also has potent adjuvant properties.

Acylation of the lipooligosaccharide of Haemophilus influenzae and colonization: an htrB mutation diminishes the colonization of human airway epithelial cells

Haemophilus influenzae is a commensal and opportunistic pathogen of the human airways. A number of surface molecules contribute to colonization of the airways by H. influenzae, such as adhesins, including structures found in the lipooligosaccharide (LOS). A human bronchiolar xenograft model was employed to investigate the host-bacterial interactions involved in the colonization of the airway by H. influenzae. Differential display was used to identify H. influenzae mRNA that reflect genes which were preferentially expressed in the xenograft compared to growth. Eleven mRNA fragments had consistent increased expression when the bacteria grew in xenografts. On sequencing these fragments, eight open reading frames were identified. Three of these had no match in the NCBI or the TIGR database, while an additional three were homologous to genes involved in heme or iron acquisition and utilization: two of the mRNAs encoded proteins homologous to enzymes involved in LOS biosynthesis: a heptosyl transferase (rfaF) involved in the synthesis of the LOS core and a ketodeoxyoctonate phosphate-dependent acyltransferase (htrB) that performs one of the late acylation reactions in lipid A synthesis. Inoculation of human bronchiolar xenografts revealed a significant reduction in colonization capacity by htrB mutants. In vitro, htrB mutants elicited lesser degrees of cytoskeletal rearrangement and less stimulation of host cell signaling with 16HBE14o(-) cells and decreased intracellular survival. These results implicate acylation of H. influenzae lipid A as playing a key role in the organisms' colonization of the normal airway.

Novel cytoplasmic proteins of nontypeable Haemophilus influenzae up-regulate human MUC5AC mucin transcription via a positive p38 mitogen-activated protein kinase pathway and a negative phosphoinositide 3-kinase-Akt pathway

Nontypeable Haemophilus influenzae (NTHi) is an important human pathogen that causes chronic otitis media with effusion (COME) in children and exacerbation of chronic obstructive pulmonary disease (COPD) in adults. Mucin overproduction, a hallmark of both diseases, has been shown to directly cause conductive hearing loss in COME and airway obstruction in COPD. The molecular mechanisms underlying mucin overproduction in NTHi infections still remain unclear. Here, we show that NTHi strongly up-regulates MUC5AC mucin transcription only after bacterial cell disruption. Maximal up-regulation is induced by heat-stable bacterial cytoplasmic proteins, whereas NTHi surface membrane proteins induce only moderate MUC5AC transcription. These results demonstrate an important role for cytoplasmic molecules from lysed bacteria in the pathogenesis of NTHi infections, and may well explain why many patients still have persistent symptoms such as middle ear effusion in COME after intensive antibiotic treatment. Furthermore, our results indicate that activation of p38 mitogen-activated protein kinase is required for NTHi-induced MUC5AC transcription, whereas activation of phosphoinositide 3-kinase-Akt pathway leads to down-regulation of NTHi-induced MUC5AC transcription via a negative cross-talk with p38 mitogen-activated protein kinase pathway. These studies may bring new insights into molecular pathogenesis of NTHi infections and lead to novel therapeutic intervention for COME and COPD.

Fine tangled pili expressed by Haemophilus ducreyi are a novel class of pili

Haemophilus ducreyi synthesizes fine, tangled pili composed predominantly of a protein whose apparent molecular weight is 24,000 (24K). A hybridoma, 2D8, produced a monoclonal antibody (MAb) that bound to a 24K protein in H. ducreyi strains isolated from diverse geographic locations. A lambda gt11 H. ducreyi library was screened with MAb 2D8. A 3.5-kb chromosomal insert from one reactive plaque was amplified and ligated into the pCRII vector. The recombinant plasmid, designated pHD24, expressed a 24K protein in Escherichia coli INV alpha F that bound MAb 2D8. The coding sequence of the 24K gene was localized by exonuclease III digestion. The insert contained a 570-bp open reading frame, designated ftpA (fine, tangled pili). Translation of ftpA predicted a polypeptide with a molecular weight of 21.1K. The predicted N-terminal amino acid sequence of the polypeptide encoded by ftpA was identical to the N-terminal amino acid sequence of purified pilin and lacked a cleavable signal sequence. Primer extension analysis of ftpA confirmed the lack of a leader peptide. The predicted amino acid sequence lacked homology to known pilin sequences but shared homology with the sequences of E. coli Dps and Treponema pallidum antigen TpF1 or 4D, proteins which associate to form ordered rings. An isogenic pilin mutant, H. ducreyi 35000ftpA::mTn3(Cm), was constructed by shuttle mutagenesis and did not contain pili when examined by electron microscopy. We conclude that H. ducreyi synthesizes fine, tangled pili that are composed of a unique major subunit, which may be exported by a signal sequence independent mechanism.

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.

The major outer membrane protein of Haemophilus ducreyi is a member of the OmpA family of proteins

Haemophilus ducreyi contains a major outer membrane protein (MOMP) whose apparent molecular weight is 39,000 to 42,000 for all strains tested. Two monoclonal antibodies (MAbs), designated 9D12 and 2C7, bound to the MOMP for all strains of H. ducreyi tested. As reported previously, MAb 9D12 was H. ducreyi specific (E. J. Hansen and T. A. Loftus, Infect. Immun. 44:196-198, 1984). MAb 2C7 bound to all members of the family Pasteurellaceae tested, suggesting that the MAbs bound to distinct epitopes on the MOMP. The MOMP was purified by extraction of whole cells with Zwittergent and ion-exchange chromatography. A peak eluted from a cation-exchange column contained three bands. All three species bound both MAbs, and the fraction yielded a single N-terminal amino acid sequence, suggesting that the bands represented different conformations of the MOMP. The MOMP was heat modifiable, contained two cysteine residues, and was cationic at pH 8.0, features not usually associated with classical porin proteins. The N-terminal amino acid sequence and total amino acid content of the MOMP were homologous to the OmpA proteins of members of the family Enterobacteriaceae and the OmpA-like protein of Actinobacillus actinomycetemcomitans. An OmpA-specific polyclonal serum bound to the MOMP, and MAb 2C7 bound to Haemophilus influenzae protein 5, an OmpA-like protein, indicating that the MOMP was antigenically related to OmpA. These data indicated that the most abundant protein in the outer membrane of H. ducreyi was not a classical porin and belonged to the OmpA family of proteins.

Characterization of an antigenically conserved heat-modifiable major outer membrane protein of Branhamella catarrhalis

Branhamella catarrhalis is a common cause of otitis media in children and of respiratory infections in adults with chronic bronchitis. Little is known about the antigenic structure of the outer membrane proteins (OMPs). In this study, two murine monoclonal antibodies, 7D6 and 5E8, were developed and used to characterize the major heat-modifiable OMP (OMP C/D) of B. catarrhalis. Immunoblot assays indicated that OMP C/D is heat modifiable, having a molecular mass of 55 kDa at room temperature and a mass of 60 kDa when heated under reducing conditions. Expression of the epitopes is independent of growth phase and growth media. Both epitopes are present in 51 of 51 strains of B. catarrhalis tested and are highly specific for Branhamella strains, being absent from a variety of other gram-negative species. Antibody 5E8 recognizes an epitope which is expressed on the surface of the intact bacterium. We conclude that OMP C/D is a major, heat-modifiable OMP antigen that expresses at least one stable, conserved epitope on the surface of B. catarrhalis. Future studies should focus on the role of OMP C/D in pathogenesis and on its potential role as a vaccine antigen.

Characterization of an 18,000-molecular-weight outer membrane protein of Haemophilus ducreyi that contains a conserved surface-exposed epitope

Identification of antigenically conserved surface components of Haemophilus ducreyi may facilitate the development of reagents to diagnose and prevent chancroid. A hybridoma derived from a mouse immunized with nontypeable Haemophilus influenzae produced a monoclonal antibody (MAb), designated 3B9, that bound to 35 of 35 H. ducreyi strains isolated from diverse geographic regions. The MAb 3B9 bound to a non-heat-modifiable H. ducreyi outer membrane protein (OMP) whose apparent molecular weight was 18,000 (the 18K OMP), and the 3B9 epitope did not phase vary at a rate of greater than 10(-3) in H. ducreyi. In immunoelectron microscopy, the 3B9 epitope was surface exposed, and there was intrastrain and interstrain variability in the amount of 3B9 labelling of whole cells. The MAb 3B9 cross-reacted with many species of the family Pasteurellaceae and bound to the 16.6K peptidoglycan-associated lipoprotein (P6 or PAL) of H. influenzae. Unlike P6, the 18K OMP did not copurify with peptidoglycan. In Western blots (immunoblots), five of seven serum samples obtained from patients with chancroid and four of five serum samples obtained from patients with other genital ulcer diseases at the time of presentation contained antibodies that bound to the 18K OMP. In a competition enzyme-linked immunosorbent assay, four of these serum samples inhibited the binding of 3B9 to H. ducreyi by more than 50%. We conclude that members of Pasteurellaceae expressed a conserved epitope on OMPs that sometimes had different physical characteristics. Patients with chancroid usually have antibodies to the 18K OMP and the 3B9 epitope that may have resulted from infection with H. ducreyi or previous exposure to other Haemophilus or Actinobacillus sp. strains.

Cloning and expression in Escherichia coli of a Haemophilus influenzae type b lipooligosaccharide synthesis gene(s) that encodes a 2-keto-3-deoxyoctulosonic acid epitope

The composition of lipooligosaccharide (LOS) can modify the virulence of Haemophilus influenzae type b (Hib). A genomic library of Hib strain A2 was constructed in the lambda bacteriophage EMBL3. Twenty-six phage clones expressed a Hib LOS oligosaccharide epitope in Escherichia coli that was detected by the monoclonal antibody (MAb) 6E4. None of the clones bound a polyclonal sera specific for Hib A2 LOS or an anti-H. influenzae lipid A MAb. One clone, designated EMBLOS-1, assembled an oligosaccharide with an apparent molecular weight of 1,400 (the 1.4K oligosaccharide) on a 4.1K lipopolysaccharide (LPS) species in E. coli LE392 and produced a novel 5.5K LPS that bound 6E4. Binding of 6E4 to the 5.5K EMBLOS-1 LPS band was abolished by treatment with sodium metaperiodate but was not affected by digestion with proteinase K, confirming the carbohydrate nature of the epitope. The EMBLOS-1 Haemophilus insert hybridized to similar restriction fragments in type b and nontypeable strains regardless of whether they expressed the 6E4 epitope. The 6E4 epitope did not undergo phase variation in Hib strain A2 at a frequency of greater than 10(-3). The oligosaccharide of the Salmonella minnesota Re mutant and 2-keto-3-deoxyoctulosonic acid (KDO) inhibited binding of 6E4 to Hib A2 LOS. We conclude that a gene(s) encoding an enzyme(s) that assembles a stable Hib LOS epitope containing KDO is conserved in H. influenzae and that the cloned Hib LOS synthesis gene products assemble a Hib LOS epitope on an E. coli K-12 LPS core.

Lipooligosaccharide epitopes shared among gram-negative non-enteric mucosal pathogens

The non-enteric Gram-negative human pathogens, B. catarrhalis, H. ducreyi, H. influenzae, N. gonorrhoeae and N. meningitidis, do not have repeating O-antigens as part of their principle surface glycolipid, the lipooligosaccharide (LOS). Because they have similar LOS structures, we studied the conservation of LOS oligosaccharide epitopes among these organisms. Twenty-one monoclonal antibodies (mAbs) generated by immunizing mice with H. influenzae, N. gonorrhoeae and N. meningitidis were studied for cross reactivity. Five mAbs generated against non-typable H. influenzae were the only strain-specific antibodies. Ten mAbs reacted to LOS epitope(s) common to a genera or species, and six mAbs bound to epitope(s) on the LOS of strains from different genera. Some cross reactive mAbs bound to LOS bands of similar molecular weights, while others bound to bands of varying molecular weights. mAb 3F11, whose epitope mimics a human blood-group antigen, bound to a 4.8 kDa LOS band in N. gonorrhoeae and H. ducreyi, two pathogens that infect genital epithelium. mAb 3D9, whose epitope consists of 2-keto-3-deoxyoctulosonic acid (KDO), reacted with different LOS bands in N. gonorrhoeae, H. influenzae and some R mutants of S. minnesota. A 14 kb restriction fragment containing lipooligosaccharide synthesis genes responsible for the assembly of the 3D9 epitope in H. influenzae hybridized to all H. influenzae strains tested but did not hybridize to gonococcal and S. minnesota strains that expressed this epitope. These studies demonstrate that conserved LOS epitope(s) exist among different species and genera of non-enteric human pathogens and that different genetic mechanisms may have evolved in these pathogens to assemble some of these conserved epitopes.

Increased resolution of lipopolysaccharides and lipooligosaccharides utilizing tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis

We utilized the recently described tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (TSDS-PAGE) system to study the lipooligosaccharides (LOS) and lipopolysaccharides (LPS) of gram negative bacteria. TSDS-PAGE resulted in a high degree of resolution of LOS and LPS in the 'mini-gel' format. TSDS-PAGE resulted in the LOS and LPS migrating as a function of their Mr during electrophoresis and allowed estimation of Mr from a protein standard. Several species of LOS were analyzed. The newly described procedure allowed a more rapid and accurate analysis of LOS and the core region of LPS.

Antigenic evidence for simultaneous expression of two different lipooligosaccharides by some strains of Haemophilus influenzae type b

Isolates of Haemophilus influenzae type b (Hib) can be divided into three antigenic groups based on their reactivities with a set of two monoclonal antibodies (MAbs) directed against epitopes in the oligosaccharide region of Hib lipooligosaccharide (LOS) (P. A. Gulig, C. C. Patrick, L. Hermanstorfer, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 55:513-520, 1987). Approximately 24% of Hib strains react with both of these LOS-specific MAbs. Immunoprecipitation experiments involving several of these strains indicated that the epitopes recognized by these MAbs resided in two different LOS molecules, both of which were synthesized by these particular Hib strains. In addition, Western blot (immunoblot) analysis of proteinase K-treated cell extracts of these strains that had been subjected to sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis revealed two different LOS staining patterns when they were probed independently with the two MAbs. Colony blot radioimmunoassay of hundreds of colonies of one of these Hib strains showed that each colony bound both MAbs. Immune electron microscopy confirmed that individual cells of this same Hib strain expressed both types of LOS molecule at the same time. An antibody accessibility radioimmunoassay was used to show that different Hib strains of this type varied in the relative amounts of each of the two MAbs that they could bind to their cell surfaces. These findings indicate that some Hib strains can synthesize two antigenically distinct LOS molecules simultaneously.

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.

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.

Cloning and sequencing of Haemophilus influenzae outer membrane protein P6

P6, a 16,600-dalton protein present in the outer membranes of both typeable and nontypeable strains, may be an important antigen in immunity to Haemophilus influenzae. The gene encoding P6 of a nontypeable strain of H. influenzae was cloned by using bacteriophage lambda gt11. Four recombinant phages were detected by screening plaques with monoclonal antibodies and a polyclonal antiserum. One recombinant phage, clone O, produced a full-length gene product which was expressed at a high yield. The DNA insert contained within this phage was cloned into the plasmid vector pUC18 to create the recombinant plasmid pBUD1. An Escherichia coli transformant containing this plasmid produced a protein which had an apparent molecular weight identical to that of H. influenzae P6, as determined by Western blot (immunoblot) analyses. Expression of the P6 polypeptide by both clone 0 and the transformant was independent of induction of the lac operon by isopropyl-beta-D-thiogalactopyranoside, suggesting that transcription was from the promoter of the P6 gene. Immunoelectron microscopy using a monoclonal antibody with specificity for a P6 surface epitope detected the presence of P6 on the surface of the transformant. The insert in pBUD1 was cut down in size to approximately 800 base pairs. The resultant plasmid, pBUD5, also coded for a full-length gene product. DNA sequence analysis revealed that the P6 gene contains transcriptional and translational sequences resembling those recognized in E. coli and a signal sequence characteristic of procaryotic membrane proteins. In addition, the carboxy terminus of this signal sequence shares homology with a common sequence found in bacterial lipoproteins, suggesting that P6 is a lipoprotein. Posttranslational proteolytic cleavage of the signal sequence would result in a protein composed of 134 amino acids.

Antigenic characterization of the oligosaccharide portion of the lipooligosaccharide of nontypable Haemophilus influenzae

Monoclonal antibodies (MAbs) directed against epitopes in the oligosaccharide portion of the lipooligosaccharide (LOS) of nontypable Haemophilus influenzae (NTHI) were used to characterize the LOS of this pathogen. Western blot (immunoblot) analysis with four LOS-specific MAbs and proteinase K-derived LOS preparations from 69 NTHI strains allowed the classification of these strains into nine LOS antigenic groups. The use of these MAbs in a more sensitive colony blot radioimmunoassay system together with these same NTHI strains identified 14 LOS antigenic groups. Extensive cross-reactivity was detected between the LOS epitopes of these NTHI strains and the LOS of H. influenzae type b. The epitopes recognized by these MAbs were not accessible to antibody on the surface of every strain. These LOS epitopes were also not stably expressed by NTHI growing in vitro; the observed frequency of LOS antigen variation ranged from 1 to 24% when large numbers of colonies of NTHI strains were screened for reactivity with the LOS-directed MAbs in the colony blot radioimmunoassay. This LOS antigenic variation was sometimes associated with alterations in the profile of the LOS molecule as resolved by dodecyl sulfate-polyacrylamide gradient gel electrophoresis followed by staining with silver. These data indicate that considerable antigenic diversity exists among NTHI strains with regard to the oligosaccharide epitopes in their LOS molecules.

Expression of a cloned lipopolysaccharide antigen from Neisseria gonorrhoeae on the surface of Escherichia coli K-12

A gonococcal gene bank maintained in Escherichia coli K-12 was screened by colony immunoblotting, and a transformant expressing a surface antigen reactive to anti-gonococcal outer membrane antiserum was isolated. The isolate carried a recombinant plasmid, pTME6, consisting of approximately 9 kilobases of Neisseria gonorrhoeae DNA inserted into the BamHI site of pBR322. Surface labeling of E. coli HB101(pTME6) confirmed that the antigen was expressed on the E. coli cell surface. The antigenic material was resistant to proteinase K digestion and sensitive to periodate oxidation, indicating that the material was carbohydrate. Purified lipopolysaccharide (LPS) from HB101(pTME6) produced a unique band on silver-stained polyacrylamide gels that contained immunoreactive material as seen on Western blots of LPS samples. Only two of three E. coli LPS mutant strains carrying pTME6 reacted with the antigonococcal antiserum, suggesting that a certain E. coli core structure is necessary for antigen expression. We conclude that pTME6 contains one or more gonococcal genes encoding an LPS core biosynthetic enzyme(s) which can modify E. coli core LPS to produce a gonococcuslike epitope(s).

Antigenic diversity of lipooligosaccharides of nontypable Haemophilus influenzae

The lipooligosaccharides (LOS) of nontypable Haemophilus influenzae are an antigenically heterogeneous group of macromolecules. Immunodiffusion and enzyme-linked immunosorbent assay inhibition studies with phenol-water-extracted LOS and absorbed antisera specific for the oligosaccharide portion of the LOS identified six LOS strain-specific antigens. To facilitate screening large numbers of strains to search for LOS antigenic heterogeneity, a system utilizing proteinase K whole cell digests in Western blots was developed. Seventy-two nontypable H. influenzae LOS extracts were analyzed in this Western blot assay. Thirty-seven of these extracts could be segregated into 10 antigenically distinct LOS groups based on immunologic recognition by one or more of the rabbit antisera. Thirty-five of the strains did not contain these LOS antigens. These results demonstrate that antigenic differences exist among the LOS of nontypable H. influenzae strains, and this heterogeneity has the potential to be used to establish an LOS-based serogrouping system.

Conservation of epitopes in the oligosaccharide portion of the lipooligosaccharide of Haemophilus influenzae type b

The antigenic characteristics of the lipooligosaccharide (LOS) of Haemophilus influenzae type b (Hib) were examined in strains obtained over an extended period of time. These Hib strains were isolated from patients with systemic Hib disease in Dallas, Tex., over a 20-year period and in New York City between 1941 and 1956. The antigenic characteristics of the LOS of these Hib strains were examined by using a set of four murine monoclonal antibodies directed against epitopes present in the oligosaccharide portion of the LOS molecule. The same basic set of LOS antigenic determinants that is expressed by recent Hib isolates was also found to be present in this collection of Hib strains spanning a 40-year period. Some variation with time was detected in the distribution of the systemic disease isolates among four Hib LOS antigenic groups; however, only 2 of 188 Hib isolates failed to react with a set of two LOS-specific monoclonal antibodies. Therefore, little variation has occurred among Hib strains with regard to the LOS epitopes defined by these monoclonal antibodies over a considerable period of time.

Antigenic characterization of the P6 protein of nontypable Haemophilus influenzae

The purpose of this study was to characterize the degree of antigenic heterogeneity or conservation of a 16,600-dalton outer membrane protein (P6) among strains of nontypable Haemophilus influenzae. Immunization of rabbits with P6 isolated from individual strains resulted in antibody to P6 of all 25 strains tested. The titers of antibody in the sera were similar among the strains. Whole organisms of two strains were used to immunize rabbits, and antibodies were produced to P6 of all strains tested. Monoclonal antibodies developed to P6 from mice immunized with whole cells of three different strains recognized determinants on P6 of all 25 strains tested. Finally, pooled normal human serum contained antibodies to P6 of all 25 strains assayed. These studies indicate that P6 is a highly conserved antigen on the outer membrane of nontypable H. influenzae.

Identification of a 16,600-dalton outer membrane protein on nontypeable Haemophilus influenzae as a target for human serum bactericidal antibody

A 16,600-D outer membrane protein is present in all strains of Haemophilus influenzae and antibodies to this protein are present in human serum. This study was designed to assess the role of this outer membrane protein (P6) in nontypeable H. influenzae as a target for human serum bactericidal antibody. P6 was isolated and coupled to an affinity column. Depleting normal human serum of antibodies to P6 by affinity chromatography resulted in reduced bactericidal activity of that serum for nontypeable H. influenzae. Immunopurified antibodies to P6 from human serum were bactericidal. Finally, preincubation of bacteria with a monoclonal antibody that recognizes a surface epitope on P6, inhibited human serum bactericidal killing. Taken together, these experiments establish that P6 is a target for human bactericidal antibodies. This observation provides evidence that P6 plays a potentially important role in human immunity to infection by nontypeable H. influenzae.

Antigenic heterogeneity of outer membrane proteins of nontypable Haemophilus influenzae is a basis for a serotyping system

A serotyping system for nontypable Haemophilus influenzae (NTHI) was developed by using isolated outer membrane protein (OMP) preparations and rabbit antisera. OMPs of 23 strains were isolated by molecular sieve chromatography of outer membranes in 1.5% sodium deoxycholate buffer. These OMP preparations were relatively free of lipopolysaccharide as determined by silver staining of sodium dodecyl sulfate gels and by dot assay with a monoclonal antibody which is specific for the lipid A of H. influenzae. Three antisera raised to whole organisms were used to serotype 21 of 23 strains with a kinetic enzyme-linked immunosorbent assay. Digestion of OMP preparations with proteinase K removed greater than 90% of the antigenic reactivity, indicating that the system is based on OMP antigens. Marked antigenic heterogeneity of OMPs exists among strains of NTHI. By determining the pattern of serological reactivity of OMPs with the three antisera, isolates were divided into groups based on antigenic differences. Six serotypes were identified. This OMP serotyping system is based on multiple antigenic determinants. Future studies will focus on identifying serotype-specific epitopes to further refine this serological classification scheme for NTHI.