IDO1 and infection: The genes whose expression was most strongly associated with TP were MZB1, MMP9, CXCL5, PDGFB, TGFB1, IL17A, S100A4, IL8, S100A7, SPARCL1, and IDO1. In order to investigate whether individuals prone to TP (TP was detected at any time point) responded differently to C. trachomatis infection than individuals not prone to TP (in whom TP was never detected throughout the study duration), random effects linear regression models were repeated and included an interaction term between infection and whether any TP was detected.