Although the pathologic consequences of C. trachomatis genital infection are well-established, the mechanism(s) that result in chlamydia-induced tissue damage are not fully understood. We have reviewed in vitro, animal, and human data related to the pathogenesis of chlamydial disease in an effort to better understand how reproductive sequelae result from C. trachomatis infection. Abundant in vitro data suggest the inflammatory response to chlamydiae is initiated and sustained by actively infected non-immune host epithelial cells. The mouse model indicates a critical role for chlamydia-activation of the innate immune receptor, toll-like receptor 2 (TLR2), and subsequent inflammatory cell influx and activation which contributes to the development of chronic genital tract tissue damage. Data from recent vaccine studies in the murine model and from human immunoepidemiologic studies support a role for chlamydia-specific CD4 Th1-IFN-γ-producing cells in protection from infection and disease. However, limited evidence obtained using animal models of repeated infection indicates that while the adaptive T cell response is a key mechanism involved in controlling or eliminating infection, it may have a double-edged nature, and contribute to tissue damage. Important immunologic questions include whether anamnestic CD4 T cell responses drive disease rather than protect against disease, and the role of specific immune cells and inflammatory mediators in the induction of tissue damage with primary and repeated infections. Continued study of the complex molecular and cellular interactions between chlamydiae and their host, and large-scale prospective immunoepidemiologic and immunopathologic studies are needed to address gaps in our understanding of pathogenesis, which thwart development of optimally effective control programs including vaccine development.

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The major outer membrane protein (MOMP) of Haemophilus ducreyi is an OmpA homolog that migrates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels as three species with apparent molecular weights ranging from 37,000 to 43,000. Monoclonal antibodies directed against this macromolecule were used to identify recombinant clones containing fragments of the gene encoding this protein. Nucleotide sequence analysis of these fragments confirmed that the MOMP encoded by the intact gene (momp) was a member of the OmpA family of outer membrane proteins. Construction of an isogenic H. ducreyi mutant unable to express the MOMP led to the discovery of a second outer membrane protein which migrated at the same rate on SDS-PAGE gels as the MOMP. N-terminal amino acid sequence analysis of this second protein revealed that its N terminus was nearly identical to that of the MOMP and also had homology with members of the OmpA family. Nucleotide sequence analysis of the region downstream from the momp gene revealed the presence of a partial open reading frame encoding a predicted OmpA-like protein. A modification of anchored PCR technology was used to obtain the nucleotide sequence of this downstream gene which was shown to encode a second OmpA homolog (OmpA2). The N-terminal amino acid sequence of OmpA2 was identical to that of the OmpA-like protein detected in the momp mutant. The H. ducreyi MOMP and OmpA2 proteins, which comigrated on SDS-PAGE gels and which were encoded by the tandem arranged momp and ompA2 genes, were 72% identical.

Nontypeable Haemophilus influenzae (NTHI) is an important cause of lower respiratory tract infections in patients with chronic obstructive pulmonary disease. Recent findings suggest that the major outer membrane protein P2 should be reconsidered as a vaccine candidate for NTHI. A P2-based vaccine would require a relative degree of sequence stability of the gene encoding P2 (ompP2) during colonization. To characterize the sequence stability of ompP2 during colonization of the human respiratory tract, ompP2 genes from 13 sets of isolates that persisted in patients with chronic obstructive pulmonary disease (mean colonization, 7 months) were sequenced. In 9 sets of isolates, ompP2 did not change. Sequence changes were noted in 4 sets of isolates. Most of these changes occurred within areas of repetitive DNA, suggesting that this type of DNA has a role in antigenic variation of P2. The sequence of ompP2 is relatively stable during persistence of NTHI in the human host.

Haemophilus ducreyi expresses an 18,000-molecular-weight outer membrane protein that contains a conserved surface-exposed epitope recognized by monoclonal antibody 3B9. Monoclonal antibody 3B9 cross-reacts with proteins of similar molecular weight found in many Haemophilus sp. strains, including P6, a candidate vaccine for Haemophilus influenzae. The gene encoding the 18,000-molecular-weight outer membrane protein was identified by screening a gt11 genomic library with 3B9. The coding sequence of the gene was localized to a 471-bp open reading frame, designated pal (peptidoglycan-associated lipoprotein). Translation of pal predicted a mature polypeptide with a molecular weight of 15,000 that had extensive homology with P6 and Escherichia coli PAL. The predicted signal peptide had features characteristic of a prokaryotic lipoprotein, and processing of PAL was sensitive to globomycin in H. ducreyi. The sequences encoding mature H. ducreyi PAL were subcloned into the vector pRSET B and expressed as a polyhistidine-containing fusion protein that bound 3B9. In Western blot (immunoblot) analysis, serum samples obtained from healthy subjects and patients with chancroid or other genital ulcer diseases contained antibodies to purified PAL. Antibodies that bound to PAL were removed by absorption with a lysate of Haemophilus sp. antigens, suggesting that patients with chancroid do not develop an H. ducreyi-specific antibody response to PAL.

Outer membrane protein E (OMP E) is a 50-kDa protein of Moraxella catarrhalis which possesses several characteristics indicating that the protein will be an effective vaccine antigen. To study the antigenic structure of OMP E, eight monoclonal antibodies were developed and characterized. Three of the antibodies recognized epitopes which are present on the bacterial surface. Fusion peptides corresponding to overlapping regions of OMP E were constructed, and immunoblot assays were performed to localize the areas of the molecule bound by the monoclonal antibodies. These studies identified a surface-exposed epitope in the region of amino acids 80 through 180. To further study the protein, two mutants which lack OMP E were constructed. In bactericidal assays, the mutants were more readily killed by normal human serum compared to the isogenic parent strains. These results indicate that OMP E is involved in the expression of serum resistance of M. catarrhalis.Moraxella catarrhalis is an important human respiratory tract pathogen (6,8,9,21,22). It is the third most common cause of otitis media, accounting for 15 to 20% of all episodes based on cultures of middle ear fluid obtained by tympanocentesis (13,29). M. catarrhalis also causes lower respiratory tract infections, often called exacerbations, in adults with chronic obstructive pulmonary disease (COPD) (23,25). It is difficult to state precisely the etiology of exacerbations in individual patients; however, one study estimated that approximately 30% are caused by M. catarrhalis (33). Nosocomial outbreaks of respiratory tract infections caused by M. catarrhalis have been recognized since the mid-1980s (18, 20, 26-28). Many of these outbreaks of infections have occurred in respiratory units where the presence of a susceptible population with underlying lung disease contributed to the clusters.In view of the importance of M. catarrhalis as a human pathogen, there is interest in developing a vaccine to prevent these infections. Two populations would benefit most from such a vaccine. Infants would be immunized in an effort to prevent otitis media, with particular emphasis on preventing recurrent otitis media in otitis-prone children. The second population that would benefit from such a vaccine is adults with COPD.Outer membrane protein E (OMP E) is a 50-kDa heatmodifiable outer membrane protein (OMP) which has characteristics that indicate that it may be an effective vaccine antigen (2, 3). The protein is abundantly expressed on the bacterial surface as demonstrated by immunofluorescence assays and flow cytometry with monoclonal antibodies (MAbs) (3). OMP E is highly conserved among strains of M. catarrhalis (2, 3). These two features of OMP E suggest that inducing an immune response to the protein may result in protection from infection.The present study was undertaken to further characterize the antigenic structure of OMP E. MAbs were developed and characterized. The regions of the OMP E molecule bound by the MAbs were identified, and two mutants which are defective in...

An adult with chronic obstructive pulmonary disease was monitored prospectively for 2 years. Nontypeable Haemophilus influenzae was isolated from sputum cultures at 22 of 23 monthly clinic visits. Analysis of the isolates, by pulsed-field gel electrophoresis (PFGE), revealed that the patient was colonized by 3 different strains during the 2-year period. The gene encoding outer-membrane protein (OMP) P2, ompP2, was amplified from sputum samples and selected strains obtained from this patient. Analysis of the ompP2 sequences, in combination with the PFGE patterns, indicated that ompP2 horizontal transfer between 2 strains occurred in the respiratory tract, between clinic visits 13 and 14. Observation of ompP2 horizontal transfer in the human respiratory tract has important implications for both the understanding of ompP2 diversity among strains and the future design of OMP P2-based vaccines.

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