Per Mygind

Molecular biology of Chlamydia pneumoniae surface proteins and their role in immunopathogenicity

BACKGROUND The association of Chlamydia pneumoniae with the development of atherosclerosis is based on serology and on detection of C pneumoniae-specific DNA by polymerase chain reaction in the atheromas. METHODS AND RESULTS Because the humoral immune response frequently recognizes epitopes present on the surface of the bacteria, we analyzed what components are present on the C pneumoniae surface. We identified a family of proteins, the GGAI or Omp4-15 proteins, of which at least 3 are present on the surface of C pneumoniae. We immunized rabbits with recombinant GGAI proteins and used these antibodies in immunofluorescence microscopy of experimentally infected mice. In lung sections, a massive infiltration with polymorph nuclear neutrophil cells was observed. In the bronchial epithelial cells, C pneumoniae inclusions were seen. Evidence was found of differential expression of the GGAI proteins. CONCLUSIONS On the basis of surface localization, differential expression, and the fact that the proteins are recognized by the human humoral immune response, we speculate whether these proteins, in addition to the lipopolysaccharides, are of importance for the immunopathogenesis of C pneumoniae.

DETECTION OF CHLAMYDIA TRACHOMATIS SPECIFIC ANTIBODIES IN HUMAN SERA BY RECOMBINANT MAJOR OUTER-MEMBRANE PROTEIN POLYANTIGENS

This study was performed to generate and evaluate recombinant antigens for use in a species-specific Chlamydia trachomatis immunoassay. In a molecular genetic approach, fragments of the C. trachomatis major outer-membrane protein (MOMP) were produced as fusion proteins to create three different constructs encompassing the variable domains I, II and IV of selected C. trachomatis serovars. The recombinant MOMP polyantigens were affinity-purified and used in an enzyme-linked immunosorbent assay. Antibody detection was evaluated with 103 patient sera and the results were compared with titres obtained in the micro-immunofluorescence test. The results showed that the generated MOMP polyantigens detected the presence of C. trachomatis-specific human antibodies with little cross-reaction to C. pneumoniae-specific antibodies. When compared to the micro-immunofluorescence assay the MOMP polyantigen detected the presence of anti-C. trachomatis IgG antibodies with a sensitivity of 80% and a specificity of 91%.

Molecular biology and serodiagnostics of Chlamydia pneumoniae — potential way to a vaccine

In Chlamydia, the obligate intracellular human pathogen with a unique biphasic life cycle, surface structures are of importance for induction of uptake in host cells, for protection of Chlamydiae at the extracellular stage, and as immunogens to which the host’s humoral immune response is directed. In contrast to C. trachomatis, in which a major immunogen is the surface-localized major outer membrane protein (MOMP) [1], this protein is non-immunogenic in C. pneumoniae infections [2]. C. pneumoniae causes upper respiratory tract infections [3], pneumonia, and is suspected to playa role in the development of atherosclerosis [4, 5]. Proteins that contain only conformational epitopes cover the surface of C. pneumoniae [6]. We have previously characterized a gene family of at least four members that encodes surface-localized proteins [7, 8]. We obtained the clones by screening an expression library with an antibody (pAbdOmc) generated against purified, SDS-denatured C. pneumoniae outer membrane complex (Omc) proteins [9], hereby obtaining antibodies to linear epitopes that in native Omc were nonimmunogenic [7]. By using antibodies generated to both linear and conformational epitopes of various parts of the recombinant proteins, we showed (i) that the proteins were the 97–99 kDa Omc proteins not present in C. trachomatis Omc [6]; (ii) that the 97-99 kDa proteins migrated as 73 kDa in unheated samples for SDSPAGE; (iii) that these proteins were the major immunogens in experimentally infected mice; and (iv) that the proteins were present on the surface of C. pneumoniae [7].