Identification and evaluation of a combination of chlamydial antigens to support the diagnosis of severe and invasive Chlamydia trachomatis infections.

Chlamydia trachomatis is the most common sexually transmitted organism in industrialized countries. Nucleic acid amplification testing, using non-invasively collected specimens, is considered to be the method of choice for diagnosis of chlamydial infections of the urethra and the lower genital tract. Serological testing has the potential to circumvent the problem of specimen sampling in invasive C. trachomatis infections of the upper genital tract. However, only a few defined chlamydial antigens have been used in a standardized diagnostic assay format. In this study, we used serological two-dimensional proteomic analysis to broaden the spectrum of diagnostically relevant C. trachomatis proteins. The genes encoding an assortment of already known chlamydial antigens, as well as immunogenic proteins that have not been described before, were cloned, and the recombinant proteins were purified in order to compare their diagnostic usefulness in parallel with a newly developed line immunoassay. With 189 sera collected from patients with and without C. trachomatis infection, recombinant major outer membrane protein (MOMP), chlamydial protease-like activity factor (CPAF), outer membrane protein 2 (OMP2), translocated actin-recruiting protein, and polymorphic membrane protein D (PmpD) showed the highest level of diagnostic sensitivity and specificity. In patients suffering from ascending and invasive C. trachomatis infections, such as pelvic inflammatory disease and lymphogranuloma venereum, the sensitivity reached with these proteins ranged between 71% (PmpD) and 94% (OMP2), and the specificity ranged between 82% (PmpD) and 100% (MOMP and OMP2). Recombinant thio-specific antioxidant peroxidase, ribosomal protein S1 (RpsA) and hypothetical protein 17 showed lower sensitivity but comparably high specificity, ranging from 94% to 100%. The novel line immunoassay based on defined recombinant antigens has promise for improved serodiagnosis in severe and invasive C. trachomatis infections.