Affiliation:
1. Department of Microbiology and Immunology, Uniformed Services University, Bethesda, Maryland, USA
2. Henry Jackson Foundation for the Advancement of Military Medicine, Bethesda, Maryland, USA
Abstract
ABSTRACT
Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA (gDNA). Previous bioinformatic studies have demonstrated that the genome of the human pathogen
Chlamydia trachomatis
contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here, we present our evaluation of the stimulatory potential of
C. trachomatis
gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. Utilizing reporter cell lines, we demonstrate that purified gDNA from
C. trachomatis
can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while
C. trachomatis
is capable of signaling through hTLR9 and mTLR9 during live infections in HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion, exacerbated by the inhibition of lipooligosaccharide biosynthesis, and is significantly altered during the induction of aberrance/persistence. Our observations support the hypothesis that chlamydial gDNA is released during the conversion between the pathogen’s replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly. Given that
C. trachomatis
inclusions do not co-localize with TLR9-containing vacuoles in the pro-monocytic cell line U937, our findings also hint that chlamydial gDNA is capable of egress from the inclusion, and traffics to TLR9-containing vacuoles via an as yet unknown pathway.
Funder
DOD | Uniformed Services University of the Health Sciences
HHS | NIH | National Institute of General Medical Sciences
Publisher
American Society for Microbiology