Toll-like receptor 4 improves replication of Chlamydia trachomatis serovar D in the uroepithelial T24/83 cell line

Chlamydia trachomatis infection remains mostly symptomless but can cause tissue modulating processes like hydrosalpinx, pelvic inflammatory disorder or lead to infertility. Uroepithelium is the point of entry for the chlamydial infection. In order to identify the immune signaling cascades activated by Chlamydia, compared to polyI:C or LPS, we infected T24/83 human uroepithelial cell line with C. trachomatis serovar D. Here we used microarray analysis and quantitative Real Time PCR, and observed an induction in the mRNA transcription of inflammatory genes such as il-1β, il-6 and tnf-α. However, the ELISA showed, that the corresponding cytokines were not secreted upon infection. T24/83 cells secrete the mentioned cytokines after a stimulation with polyI:C or LPS which are ligands for Toll-like receptor (TLR) 3 and 4, respectively. Thus, the pattern of the gene induction is different compared to infection with C. trachomatis. Additionally, we identified a set of genes like matrix metallopeptidase 1 and 3 and histatin 1, which were most induced upon C. trachomatis infection. It was reported, that TLR3 and TLR4 play an important role in the host pathogen interaction. Therefore we wanted to identify the role of TLR3 and TLR4 in T24/83 cells using CRISPR/Cas9 knock-outs. Unexpectedly we could show that in TLR4KO cells C. trachomatis serovar D replicate less well than in the wildtype. Whereas TLR3KO cells showed no difference in chlamydial replication compared to the wild type host cells. Hence, we assume that chlamydia can use TLR4 as a supporter for its own growth.