Sequence variation in the hpd gene of nonencapsulated Haemophilus influenzae isolated from patients with chronic bronchitis

The molecular diversity of protein D of nonencapsulated Haemophilus influenzae strains isolated from persistently infected patients with chronic bronchitis was studied by sequencing the hpd gene of four independently obtained isolates. The nucleotide (nt) sequences of the hpd genes of two strains were identical. The other two hpd sequences showed nt substitutions which were mostly synonymous. As a consequence the deduced amino acid (aa) sequences differed from the consensus sequence only by a few aa. No changes in the hpd genes were observed among the four variants of the four strains persisting in chronic bronchitis patients for 9, 11, 8 and 3 months, respectively, although variation in their major outer membrane proteins P2 and P5 occurred. We conclude that the hpd gene is conserved during chronic infections of nonencapsulated H. influenzae.     

Identification of a second family of high-molecular-weight adhesion proteins expressed by non-typable Haemophilus influenzae

We previously reported that two surface-exposed high-molecular-weight proteins, HMW1 and HMW2, expressed by a prototypic strain of non-typable Haemophilus influenzae (NTHI), mediate attachment to human epithelial cells. These proteins are members of a family of highly immunogenic proteins common to 70–75% of NTHI strains. NTHI strains that lack HMW1/ HMW2-like proteins remain capable of efficient attachment to cultured human epithelial cells, suggesting the existence of additional adhesion molecules. We reasoned that characterization of high-molecular-weight immunogenic proteins from an HMW1/HMW2-deficient strain might identify additional adhesion proteins. A genomic library was prepared in λEMBL3 with chromosomal DNA from non-typable Haemophilus strain 11, a strain that lacks HMW1/HMW2-like proteins. The library was screened immunologically with convalescent serum from a child naturally infected with strain 11, and phage clones expressing high-molecular-weight recombinant proteins were identified by Western blot analysis. One clone was identified that expressed a protein with an apparent molecular mass greater than 200 kDa. Transformation of non-adherent Escherichia coli strain DH5α with plasmids containing the genetic locus encoding this protein gave rise to E. colitransformants that adhered avidly to Chang conjunctival cells. Subcloning and mutagenesis studies localized the DNA conferring the adherence phenotype to a 4.8 kbp fragment, and nucleotide sequence analysis further localized the gene encoding the adhesion protein to a 3.3 kbp open reading frame predicted to encode a protein of 114kDa. The gene was designated hia for Haemophilus influenzae adhesin. Southern analysis revealed an hia homologue in 13 of 15 HMW1/HMW2-deficient non-typable H. influenzae strains. In contrast, the hia gene was not present in any of 23 non-typable H. influenzae strains which expressed HMW1/HMW2-like proteins. Identification of this second family of high-molecular-weight adhesion proteins suggests the possibility of developing vaccines based upon a combination of HMW1/HMW2-like proteins and Hia-like proteins which would be protective against disease caused by most or all non-typable H. influenzae     

A novel chimeric MOMP antigen expressed in Escherichia coli, Arabidopsis thaliana, and Daucus carota as a potential Chlamydia trachomatis vaccine candidate

The major outer membrane protein (MOMP) of Chlamydia trachomatis is a highly antigenic and hydrophobic transmembrane protein. Our attempts to express the full-length protein in a soluble form in Escherichia coli and in transgenic plants failed. A chimeric gene construct of C. trachomatis serovar E MOMP was designed in order to increase solubility of the MOMP protein but with retained antigenicity. The designed construct was successfully expressed in E. coli, in Arabidopsis thaliana, and in Daucus carota. The chimeric MOMP expressed in and purified from E. coli was used as antigen for production of antibodies in rabbits. The anti-chimeric MOMP antibodies recognized the corresponding protein in both E. coli and in transgenic plants, as well as in inactivated C. trachomatis elementary bodies. Transgenic Arabidopsis and carrots were characterized for the number of MOMP chimeric genetic inserts and for protein expression. Stable integration of the transgene and the corresponding protein expression were demonstrated in Arabidopsis plants over at least six generations. Transgenic carrots showed a high level of expression of the chimeric MOMP – up to 3% of TSP.     

Phylogenetic relationships of Campylobacter jejuni based on porA sequences

Campylobacter porins are the dominant major outer membrane protein (MOMP) of these bacteria. They are composed of hypervariable, surface-exposed, peptide loops and membrane-embedded, conserved peptide regions. Porins are functionally important and may also be useful for molecular subtyping methods but have not yet been well characterized. We therefore sequenced the porA gene from 39 Campylobacter isolates, including multilocus sequence type (MLST) reference strains, isolates from patients with the Guillain-Barré syndrome, other clinical isolates, and serotyping reference strains. These were compared with additional sequences available from GenBank. Three distinct porA lineages were observed after phylogenetic analysis. Both Campylobacter coli and Campylobacter jejuni were found with group 3 porA sequences, and this was the only group showing any evidence of recombination among porA genes. There was no recombination between porA genes from C. jejuni groups 1 and 2, suggesting there may be functional constraints on changes at this locus. Most of the amino acid differences among the three groups were present in surface-exposed loops, and dissimilar substitutions were found when groups 1 and 2 MOMP were compared. Different MOMP sequence groups may have different biological or antigenic properties, which in turn may be associated with survival in different environments, host adaptation, or virulence.     

The 100 kDa haem:haemopexin-binding protein of Haemophilus Influenzae: structure and localization

All Haemophilus influenzae strains have an absolute requirement for exogenously supplied haem for aerobic growth. A majority of strains of H. influenzae type b (Hib) produce a 100 kDa protein which binds haem: haemopexin complexes. This 100 kDa haem:haemopexin binding protein, designated HxuA, was originally detected on the Hib cell surface. Monoclonal antibody (mAb)-based analyses revealed that the HxuA protein was also present in soluble form in Hib culture supernatants. This soluble HxuA protein exhibited haem:haemopexin-binding activity in a direct binding assay. Nucleotide sequence analysis of the hxuA gene from Hib strain DL42, together with N-terminal amino acid analysis of HxuA protein purified from Hib culture supernatant, revealed that this protein was synthesized as a 101 kDa precursor with a leader peptide that was removed to yield a 99kDa protein. Southern blot analysis of chromosomal DNA from four Hib and four non-typeable H. influenzae (NTHI) strains detected the presence of a single band in each strain that hybridized a Hib hxuA gene probe. Subsequent analysis of these NTHI strains showed that all four strains released into culture supernatant a haem:haemopexin-binding protein that migrated in SDS-PAGE at a rate similar or identical to that of the Hib HxuA protein. A Hib hxuA mutant was used to screen an NTHI genomic DNA library and an NTHI gene was cloned that complemented the mutation in this Hib strain. Nucleotide sequence analysis of this NTHI gene revealed that it encoded a protein with 87% identity to the Hib HxuA protein. The expression of HxuA by both Hib and NTHI strains indicates that this particular haem acquisition system is conserved among H. influenzae strains.     

Mapping the Laminin Receptor Binding Domains of Neisseria meningitidis PorA and Haemophilus influenzae OmpP2

Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae are major bacterial agents of meningitis. They each bind the 37/67-kDa laminin receptor (LamR) via the surface protein adhesins: meningococcal PilQ and PorA, H. influenzae OmpP2 and pneumococcal CbpA. We have previously reported that a surface-exposed loop of the R2 domain of CbpA mediates LamR-binding. Here we have identified the LamR-binding regions of PorA and OmpP2. Using truncated recombinant proteins we show that binding is dependent on amino acids 171–240 and 91–99 of PorA and OmpP2, respectively, which are predicted to localize to the fourth and second surface-exposed loops, respectively, of these proteins. Synthetic peptides corresponding to the loops bound LamR and could block LamR-binding to bacterial ligands in a dose dependant manner. Meningococci expressing PorA lacking the apex of loop 4 and H. influenzae expressing OmpP2 lacking the apex of loop 2 showed significantly reduced LamR binding. Since both loops are hyper-variable, our data may suggest a molecular basis for the range of LamR-binding capabilities previously reported among different meningococcal and H. influenzae strains.     

Diversity of Chlamydia trachomatis major outer membrane protein genes.

Genomic DNA libraries were constructed for Chlamydia trachomatis serovars B and C by using BamHI fragments, and recombinants that contained the major outer membrane protein (omp1) gene for each serovar were identified and sequenced. Comparisons between these gene sequences and the gene from serovar L2 demonstrated fewer base pair differences between serovars L2 and B than between L2 and C; this finding is consistent with the serologic and antigenic relationships among these serovars. The translated amino acid sequence for the major outer membrane proteins (MOMPs) contained the same number of amino acids for serovars L2 and B, whereas the serovar C MOMP contained three additional amino acids. The antigenic diversity of the chlamydial MOMP was reflected in four sequence-variable domains, and two of these domains were candidates for the putative type-specific antigenic determinant. The molecular basis of omp1 gene diversity among C. trachomatis serovars was observed to be clustered nucleotide substitutions for closely related serovars and insertions or deletions for distantly related serovars.     

Cloning and Characterization of a 22 kDa Outer-Membrane Protein (Omp22) from Helicobacter pylori

Helicobacter pylori is a causative agent of gastritis and peptic ulceration in humans. As the first step towards development of a vaccine against H. pylori infection, we have attempted to identify protective antigens. A potential target of vaccine development would be a H. pylori specific protein, which is surface-exposed and highly antigenic. We identified a 22 kDa outer-membrane protein (Omp22) from H. pylori, which was highly immunoreactive. By screening a H. pylori genomic DNA library with rabbit anti-H. pylori outer-membrane protein antibodies, the omp22 gene was cloned and 1.4 kb of the nucleotide sequence was determined. One open reading frame, encoding a 179-residue polypeptide, was identified and the amino acid sequence deduced showed homology with peptidoglycan-associated lipoproteins. The sequence was conserved among other H. pylori strains. Omp22 protein is expressed as a precursor polypeptide of 179 residues and undergoes lipid modification and cleavage of an 18 amino acid signal peptide to yield a mature protein. Omp22 protein in H. pylori as well as recombinant Omp22 protein expressed in E. coli was localized into the outer membrane and exposed on the cell surface. Omp22 may have the potential as a target antigen for the development of a H. pylori vaccine.     

Antigenic relationship betweenHaemophilus influenzae andHaemophilus isolated from porcine pleuropneumonia

Comparative double immunodiffusion techniques were used to study capsular and O antigenic relationships betweenHaemophilus influenzae types a-fandH. pleuropneumoniae types 1–5 and a strain (202) closely related toH. pleuropneumoniae. Culture fluids or culture supernatants were used as antigens and rabbit antisera were produced against cell suspensions of the strains tested. A reaction of identity was obtained between the capsular precipitate ofH. influenzae c and a precipitate formed by strain 202, when developed with anti-H. influenzae c serum or the serum produced against strain 202. Mutual cross-absorption of capsular antibodies was also demonstrable. No other capsular or O antigenic cross-reactivity was demonstrable between the strains tested.     

Molecular and genetic characterization of superoxide dismutase in Haemophilus influenzae type b

Oxygen free radicals present a serious potential threat to microbial survival, through their ability to inflict Indiscriminate damage on proteins and DNA. Superoxide dismutase (SOD, EC 1.15.1.1), among other oxygen-metabolizing enzymes, is essential to prevent these toxic molecules from accumulating in the bacterial cytosol during aerobic metabolism. The gene sodA, encoding manganese-containing SOD ([Mn]-SOD), has been cloned from a virulent strain of Haemophilus influenzae type b using degenerate oligonucleotides encoding regions of the gene conserved across different bacterial species. The gene product has been identified as [Mn]-SOD by its similarity at key amino acid residues to known examples of the enzyme, by expression of enzymatically active protein from cloned DNA expressed in Escherichia coli, and by demonstration that an in-frame deletion in the gene abolishes this activity. In contrast to the situation in E. coli, this [Mn]-SOD is the only active SOD detected in H. influenzae. In further contrast to E. coli, [Mn]-SOD gene expression in H. influenzae has been found to be only partially repressed under anaerobic conditions. When expressed in E. coli the gene is regulated by Fur and Fnr, and the promoter region, identified experimentally, has been found to contain nucleotide sequence motifs similar to the Fur- and Fnr-binding sequences of E. coli, suggesting the involvement of analogues of these aerobiosis- responsive activators in H. influenzae gene expression.     

Multiplex quantitative PCR for detection of lower respiratory tract infection and meningitis caused by <Emphasis Type="Italic">Streptococcus pneumoniae</Emphasis>, <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> and <Emphasis Type="Italic">Neisseria meningitidis</Emphasis>

Background  

Streptococcus pneumoniae and Haemophilus influenzae cause pneumonia and as Neisseria meningitidis they are important agents of meningitis. Although several PCR methods have been described for these bacteria the specificity is an underestimated problem. Here we present a quantitative multiplex real-time PCR (qmPCR) for detection of S. pneumoniae (9802 gene fragment), H. influenzae (omp P6 gene) and N. meningitidis (ctrA gene). The method was evaluated on bronchoalveolar lavage (BAL) samples from 156 adults with lower respiratory tract infection (LRTI) and 31 controls, and on 87 cerebrospinal fluid (CSF) samples from meningitis patients.     

Tandem repeats of the tetramer 5'-CAAT-3'present in lic2A are required for phase variation but not lipopolysaccharide biosynthesis in Haemophilus influenzae

A novel lipopolysaccharide (LPS) biosynthesis gene, lic2B, which is required for the biosynthesis of a phase-variable LPS structure expressed by Haemo philus influenzae RM7004 is described. The product of this gene is homologous to Lic2A and the recently described LPS biosynthetic enzymes, LgtB from Neis seria gonorrhoea and LgtE from Neisseria meningitidis, and LpsA from Pasteurella haemolytica. Of this family of enzymes only Lic2A contains the repetitive tetrapeptide motif (SINQ)ⁿ encoded by multiple tandem repeats of 5′-CAAT-3′. This observation suggested that (SINQ)ⁿ might not be a prerequisite for the catalytic activity of this protein. To address this hypothesis, we deleted the 5′-CAAT-3’repeats from lic2A so that the protein encoded by the modified gene was analogous to Lic2B. This mutation had no apparent effect on the overall apparent molecular weight of LPS as judged by Tricine-SDS-PAGE and did not affect ability to react with monoclonal antibody 4C4. It was therefore concluded that (SINQ)ⁿ is not a prerequisite for the enzymatic function of Lic2A and that the 5′-CAAT-3’repeats in lic2A function solely as a mechan ism for generating phase variation. This observation suggested that wide variation in the number of 5’-CAAT-3’repeats might be tolerated in lic2A, and this was confirmed by surveying the number of 5′-CAAT-3’repeats in a range of different H. influenzae strains. The predicted secondary structure of (SINQ)ⁿ indicates that it forms a highly flexible random coiled structure, which is unlikely to impede formation of the domains that may be required for catalytic activity. This characteristic is also a feature of repetitive tetrapeptides encoded by other tetrameric repeats located within coding sequences present on the chromosome of H. influenzae Rd.     

Patterns of predicted T-cell epitopes associated with antigenic drift in influenza H3N2 hemagglutinin

Antigenic drift allowing escape from neutralizing antibodies is an important feature of transmission and survival of influenza viruses in host populations. Antigenic drift has been studied in particular detail for influenza A H3N2 and well defined antigenic clusters of this virus documented. We examine how host immunogenetics contributes to determination of the antibody spectrum, and hence the immune pressure bringing about antigenic drift. Using uTOPE™ bioinformatics analysis of predicted MHC binding, based on amino acid physical property principal components, we examined the binding affinity of all 9-mer and 15-mer peptides within the hemagglutinin 1 (HA1) of 447 H3N2 virus isolates to 35 MHC-I and 14 MHC-II alleles. We provide a comprehensive map of predicted MHC-I and MHC-II binding affinity for a broad array of HLA alleles for the H3N2 influenza HA1 protein. Each HLA allele exhibited a characteristic predicted binding pattern. Cluster analysis for each HLA allele shows that patterns based on predicted MHC binding mirror those described based on antibody binding. A single amino acid mutation or position displacement can result in a marked difference in MHC binding and hence potential T-helper function. We assessed the impact of individual amino acid changes in HA1 sequences between 10 virus isolates from 1968–2002, representative of antigenic clusters, to understand the changes in MHC binding over time. Gain and loss of predicted high affinity MHC-II binding sites with cluster transitions were documented. Predicted high affinity MHC-II binding sites were adjacent to antibody binding sites. We conclude that host MHC diversity may have a major determinant role in the antigenic drift of influenza A H3N2.     

Binding of human factor H to outer membrane protein P5 of non‐typeable Haemophilus influenzae contributes to complement resistance

Non‐typeable Haemophilus influenzae is an opportunistic pathogen of the human upper respiratory tract and is often found to cause inflammatory diseases that include sinusitis, otitis media and exacerbations of chronic obstructive pulmonary disease. To persist in the inflammatory milieu during infection, non‐typeable H. influenzae must resist the antimicrobial activity of the human complement system. Here, we used Tn‐seq to identify genes important for resistance to complement‐mediated killing. This screen identified outer membrane protein P5 in evasion of the alternative pathway of complement activation. Outer membrane protein P5 was shown to bind human complement regulatory protein factor H directly, thereby, preventing complement factor C3 deposition on the surface of the bacterium. Furthermore, we show that amino acid variation within surface‐exposed regions within outer membrane P5 affected the level of factor H binding between individual strains.     

Mechanism of antigenic drift in influenza virus. Amino acid sequence changes in an antigenically active region of Hong Kong (H3N2) influenza virus hemagglutinin

During antigenic drift in influenza viruses, changes in antigenicity are associated with changes in amino acid sequence of the large hemagglutinin polypeptide, HA1. In ten variants of Hong Kong (H3N2) influenza virus selected with monoclonal antibodies, the proline residue at position 143 in HA1 changed to serine, threonine, leucine or histidine. In other variants, asparagine 133 changed to lysine, glycine 144 to aspartic acid and serine 145 to lysine. All these changes are possible by single base changes in the RNA except the last, which requires a double base change. Residues 142 to 146 also changed in field strains of Hong Kong influenza isolated between 1968 and 1977 (Laver et al., 1980). The single amino acid sequence changes in HA1 of the monoclonal variants were detected by comparing the compositions of the soluble tryptic peptides from the variants with the known sequences of these peptides from wild-type virus. Two insoluble tryptic peptides, comprising residues 110 to 140 and 230 to 255 in the HA1 molecule, were not examined and we do not know if additional changes occurred in these regions.In order to determine whether sequential changes at the same position occurred during antigenic drift, antibody prepared against the new antigenic site on the variants in which proline 143 changed to histidine or threonine was used to select second generation variants of these variants. In the first case, the glycine residue (144) next to the histidine changed to aspartic acid, and in the second, the threonine residue at position 143 reverted to proline and the virus regained the antigenicity of wild-type.Although monoclonal antibodies revealed dramatic antigenic differences between the variants and wild-type virus, only those variants with changes at position 144 of glycine to aspartic acid or at position 145 of serine to lysine could be distinguished from wild-type virus using heterogeneous rabbit or ferret antisera. The other variants, including those which showed sequence changes in widely separated positions of HA1, could not be distinguished from wild-type with heterogeneous antisera.These findings suggest that sequence changes in the region comprising residues 142 to 146 of HA1 affect an important antigenic site on the hemagglutinin molecule, but how these changes affect the antigenic properties, or whether this region actually forms part of the antigenic site is not known.     

Assessing Antigenic Drift of Seasonal Influenza A(H3N2) and A(H1N1)pdm09 Viruses

Under selective pressure from the host immune system, antigenic epitopes of influenza virus hemagglutinin (HA) have continually evolved to escape antibody recognition, termed antigenic drift. We analyzed the genomes of influenza A(H3N2) and A(H1N1)pdm09 virus strains circulating in Thailand between 2010 and 2014 and assessed how well the yearly vaccine strains recommended for the southern hemisphere matched them. We amplified and sequenced the HA gene of 120 A(H3N2) and 81 A(H1N1)pdm09 influenza virus samples obtained from respiratory specimens and calculated the perfect-match vaccine efficacy using the p _epitope model, which quantitated the antigenic drift in the dominant epitope of HA. Phylogenetic analysis of the A(H3N2) HA1 genes classified most strains into genetic clades 1, 3A, 3B, and 3C. The A(H3N2) strains from the 2013 and 2014 seasons showed very low to moderate vaccine efficacy and demonstrated antigenic drift from epitopes C and A to epitope B. Meanwhile, most A(H1N1)pdm09 strains from the 2012–2014 seasons belonged to genetic clades 6A, 6B, and 6C and displayed the dominant epitope mutations at epitopes B and E. Finally, the vaccine efficacy for A(H1N1)pdm09 (79.6–93.4%) was generally higher than that of A(H3N2). These findings further confirmed the accelerating antigenic drift of the circulating influenza A(H3N2) in recent years.     

Antigenic drift in influenza virus H3 hemagglutinin from 1968 to 1980: multiple evolutionary pathways and sequential amino acid changes at key antigenic sites

Surveys of the antigenic properties of a wide range of variants of the H3N2 (Hong Kong) influenza virus subtype have revealed complex patterns of variants cocirculating during each of the main epidemic eras of the subtype. We determined hemagglutinin (HA) gene sequences for 14 isolates chosen to give the wildest possible spread of variant types. The addition of these data to existing HA gene sequence information for other variants provides a comprehensive picture of HA gene evolution during antigenic drift among H3N2 subtype viruses. The data reveal the existence of multiple evolutionary pathways during at least one period of development of the subtype and strikingly demonstrate that amino acid changes are limited to a small number of locations on the HA molecule during antigenic drift. The occurrence of sequential amino acid changes at key positions within these variable regions suggests that the HA structure has remained constant during subtype evolution so that only limited possibilities remain for further antigenic drift among H3N2 viruses.     

A Haemophilus influenzae IgA protease-like protein promotes intimate interaction with human epithelial cells

Haemophilus influenzae represents a common cause of human disease and an important source of morbidity and mortality. Disease caused by this organism begins with colonization of the upper respiratory tract. Several studies indicate that H. influenzae is capable of binding to and entering cultured human cells, properties which are potentially of relevance to the process of colonization. In the present study, we isolated an H. influenzae gene designated hap, which is associated with the capacity for In vitro attachment and entry. Analysis of the derived amino acid sequence of hap demonstrated significant homology with the serine-type lgA1 proteases expressed by H. influenzae and Neisseria gonorrhoeae. It is notable that the hap product shares the catalytic domain of the lgA1 proteases and appears to be processed and secreted in an analogous manner. We speculate that the hap gene product is an important determinant of colonization, perhaps enabling the organism to evade the local immune response and thereby persist within the respiratory tract.     

An Application of Outer Membrane Protein P6-Specific Enzyme-Linked Immunosorbent Assay for Detection of Haemophilus influenzae in Middle Ear Fluids and Nasopharyngeal Secretions

An enzyme-linked immunosorbent assay specific to outer membrane protein P6 (P6-ELISA) was applied for detecting Haemophilus influenzae in middle ear fluids (MEFs) from acute otitis media (AOM) patients and in nasopharyngeal secretions (NPSs) from acute rhinosinusitis patients. P6-ELISA had a sensitivity of 83.3% for MEFs and 71.5% for NPSs and a specificity of 85.6% for MEFs and 92.5% for NPSs, respectively. Real-time PCR exhibited significant differences in the number of ompP1 gene copies among samples determined by P6-ELISA to be positive and negative for H. influenzae. However, because the P6-ELISA test has the reactivity in Haemophilus species include two commensals H. haemolyticus and H. parainfluenzae, it is thus a weak method in order to detect only NTHi correctly. Consequently, diagnosis using the P6-ELISA should be based on an overall evaluation, including the results of other related examinations and clinical symptoms to prevent misleading conclusions in clinical setting.     

Overexpression and surface localization of the Chlamydia trachomatis major outer membrane protein in Escherichia coli

The Chlamydia trachomatis major outer membrane protein (MOMP) is the quantitatively predominant surface protein which has important functional, structural and antigenic properties. We have cloned and overexpressed the MOMP in Escherichia coli. The MOMP is surface exposed in C. trachomatis and capable of eliciting protective antibodies in infected hosts, and therefore has potential as a candidate vaccine to prevent infection with this significant human pathogen. The recombinant MOMP clone, L2rMOMP, contained the entire MOMP gene including the encoded leader sequence. Large quantities of chlamydial MOMP were expressed, some of which was processed and translocated to the E. coli surface. Surface localization of the MOMP was demonstrated by the binding of anti-MOMP monoclonal antibodies to the surface of the induced clone, and was visualized by fluorescence and electron microscopy. The induction of MOMP expression had a rapidly lethal effect on the L2rMOMP E. coli clone. Although no genetic system exists for Chlamydia, development of a stable, inducible E. coli clone which overexpresses the chlamydial MOMP permits a study of the biological properties of the MOMP, including the contribution of the MOMP variable segments to the topographical interactions which determine the antigenic structure responsible for human immune response.