Differential cytokine expression in Chlamydophila psittaci genotype A-, B- or D-infected chicken macrophages after exposure to Escherichia coli O2:K1 LPS

Chlamydophila (Cp.) psittaci and avian pathogenic Escherichia (E.) coli infections contribute to the respiratory disease complex observed in turkeys. Secondary infection with E. coli exacerbates Cp. psittaci pathogenicity and augments E. coli excretion. The innate immune response initiated by both pathogens in their avian host is unknown. We therefore determined the cytokine responses following Cp. psittaci infection and E. coli superinfection of avian monocytes/macrophages by examining gene transcripts of IL-1?, IL-6, CXCLi2 (IL-8), CXCLi1 (K60), IL-10, IL-12?/?, IL-18, TGF-?4 and CCLi2 at 4 h post-inoculation with different Cp. psittaci strains or 4 h post-treatment with avian E. coli LPS of Cp. psittaci pre-infected HD11 cells. Cp. psittaci strains used were 84/55 and 92/1293 (highly virulent), CP3 (low virulent) and 84/2334 (phylogenetically intermediate between Cp. psittaci and Chlamydophila abortus). At 4 h post chlamydial infection, an increased expression of IL-1? and IL-6 as well as CXCLi2, CXCLi1 and CCLi2 was observed compared to levels in uninfected HD11 controls. This effect was less pronounced for the milder CP3 strain. The pro-inflammatory response of Cp. psittaci infected cells to E. coli LPS was significantly lowered compared to uninfected controls, especially when the cells were pre-infected with highly virulent Cp. psittaci strains. In both experiments, exceptionally high IL-10 and no TGF-?4 responses were observed, and we propose that this could induce macrophage deactivation and NF-?B suppression. Consequently, pro-inflammatory and Th1-promoting responses to both the primary Cp. psittaci infection and E. coli would be inhibited, thus explaining the observed aggravated in vivo pathology.