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].