TLR2 and chlamydia trachomatis infectious disease: To further confirm the importance of IFNγ in the host immune defense towards C. trachomatis, the response of untreated synovial cells to chlamydial infection appeared to be mediated only by the increased expression of pattern recognition receptors TLR2 and TLR3, followed by the activation of IRF9 and the expression of ISG56 and GBP1, whereas TLR4 and the pathway cGAS/STING were not engaged.