Interactions of antisera to different Chlamydia and Chlamydophila species with the ribosomal protein RPS27a correlate with impaired protein synthesis in a human choroid plexus papilloma cell line

Chlamydia trachomatis (CT) and the Chlamydophila species (CS) Chlamydophila pneumoniae (CPn), and Chlamydophila psittaci (CPs) are suggested to induce autoantibodies causative of several human autoimmune disorders like rheumatoid arthritis and systemic lupus erythematosus (SLE). The aim of the present study was therefore to identify cellular protein interaction partners with antisera to CT (α-CT) or CS (α-CS) and to identify functional consequences of such interaction in vitro. As detected with a commercial first trimester human prenatal brain multiprotein array (hEXselect, Engine, Germany), the most frequent interaction partner with both α-CT and α-CS was the ribosomal small subunit protein RPS27a. This could be confirmed by Western blot analysis with a recombinant RPS27a sample. In addition, immunocytochemistry with both antisera in the human choroid plexus papilloma cell line HIBCPP revealed a granular cytoplasmic staining, and Western blot analysis with whole-cell protein samples of HIBCPP cells revealed both antisera to label protein bands of different molecular weights and intensity. By 2D Western blot analysis and mass spectrometry, one of the protein spots interacting with α-CT could be identified as the RPS27a. Finally, two different methods for the detection of protein synthesis activity, the SUnSET technique and an HPG fluorescence assay revealed both antisera to cause reduced translational activity in HIBCPP cells. Together with previous findings of RPS27a as an autoimmune target in a mouse model of systemic lupus erythematosus (SLE), these results suggest that infections with CT and/or CS could induce SLE-associated immune modifications. However, direct evidence for a pathogenic role of these interactions for SLE demands further investigations.