Chlamydial plasmid-encoded protein pORF5 induces production of IL-1β and IL-18 via NALP3 inflammasome activation and p38 MAPK pathway

The pathogenesis of Chlamydia-induced inflammation is poorly understood. pORF5 is the only secreted protein encoded by Chlamydial plasmid. This study aims to investigate the effects of pORF5 on the production of interleukin-1 beta (IL-1 beta) and interleukin-18 (IL-18) and the underlying mechanisms of these effects. THP-1 (a human acute monocytic leukemia cell line) cells were stimulated by pORF5 with or without pretreatment with Natch domain, Leucine-rich repeat and PYD-containing protein 3 (NALP3) siRNA, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) siRNA, cysteine aspartate-specific protease-1 (caspase-1) specific inhibitor and p38 mitogen-activated protein kinase (p38 MAPK) inhibitor. IL-1 beta, IL-18 and caspase-1 expression was detected through both ELISA and qRT-PCR. NALP3 and ASC expression was detected by qRT-PCR. The expression of caspase-1 and phosphorylated-p38 MAPK was detected by western blot analysis. pORF5 induced IL-1 beta, IL-18, caspase-1 and NALP3 inflammasome expression in THP-1 cells. Caspase-1 inhibitor significantly reduced pORF5-induced IL-1 beta and IL-18 expression. The siRNAs for NALP3 inflammasome significantly reduced pORF5-induced IL-1 beta, IL-18 and caspase-1 expression. Furthermore, p38 MAPK inhibitor significantly reduced pORF5-induced IL-1 beta, IL-18, caspase-1 and NALP3 inflammasome expression. pORF5 could induce production of IL-1 beta and IL-18 via NALP3 inflammasome activation and p38MAPK pathway. pORF5 protein might play an important role in Chlamydia pathogenesis. This study provides a new insight into the molecular pathogenesis of Chlamydial diseases.