Mechanisms used by Chlamydia to subvert host innate immune responses include blocking transcription factor NF-kB activation directly through the proteolysis of the p65/RelA OTX015 mw subunit of NF-kB [54]. Virulence associated genes of Chlamydia have also recently been reported to be transcriptionally regulated by the Pgp4 protein encoded by the highly conserved 7.5kB cryptic plasmid of C. trachomatis [55]. These genes include pgp3 that encodes a protein to which immune responses are elicited in patients with C. trachomatis infection (see Table 1). Chlamydia also inhibit IFN-g-inducible major histocompatibility complex

(MHC) class II expression [56], down-regulate MHC class I heavy chain (HC) presentation

[57], and in human endocervical cells this is mediated by direct and indirect (soluble) factors [58]. The multiple potential mechanisms used by Chlamydia dampen immune responses have recently PLX3397 research buy been well summarized [50]. The consequent development of chlamydial disease following genital tract infections in humans is multifactorial and involves not only chlamydial factors such as virulence via different C. trachomatis strains but also host and environmental factors. For example, a recent prospective study of African-American women with clinically suspected mild to moderate cases of PID showed that gene polymorphisms in several innate immune receptors (including Toll-like receptors [TLR] 1 and 4) were associated with increased genital tract C. trachomatis infections [59]. The female genital tract is also a unique mucosal site in that it is influenced by fluctuating hormone levels and the polymicrobial environment. Hormone changes directly affect cell type and indirectly affect both the innate and adaptive immune responses to chlamydial genital

infections [60]. Changes in bacterial flora and genital tract inflammation are both suggested cofactors for persistence of Chlamydia at this site and affect vaginal pH, which may be associated with the risk of acquiring C. trachomatis infection [61] and [62]. The reproductive tract microbiome, sex hormones and immune responses are challenges for development of vaccines against genital tract pathogens unless and are discussed in detail in a paper in the current issue [63]. While animal models are useful and convenient, they must provide data about vaccination that will eventually be transferrable to the human situation. In the case of chlamydial STIs, the mouse model is the most widely used model for infection, pathogenesis and vaccine studies. Primary genital tract infections of female mice with elementary bodies of the mouse-adapted Chlamydia muridarum strain are enough to cause tubal dilatation since a consistent observation is the development of hydrosalpinx shortly (1–2 days) after initial chlamydial infection in this model [64].