TLR4 and chlamydia infectious disease: Furthermore, Chlamydia infection-induced CHOP expression was independent of TLR4 signalling (Fig. 5F) as blocking TLR4 signalling with the TLR4 blocking antibody, resulted in increased CHOP expression in response to C. trachomatis suggesting that induction of the ISR occurs independently of LPS and TLR4 and is therefore distinct to the activation of IRE1α and PKR.