Chlamydia trachomatis restricts signaling through NOD2 until late in the pathogen's developmental cycle

Area of Science:

• Infectious diseases
• Microbiology
• Immunology

Background:

• Pathogenic chlamydiae limit peptidoglycan (PG) to the division septum, a strategy potentially reducing recognition by innate immune receptors like nucleotide-binding oligomerization domain-containing proteins (NOD1 and NOD2).
• Chlamydia trachomatis infection activates NOD1 signaling early (8-12 hours), coinciding with the transition to replicative forms.

Purpose of the Study:

• To investigate the temporal activation of NOD2 signaling during Chlamydia infection.
• To explore the mechanisms and implications of Chlamydia-induced NOD2 signaling in host-pathogen interactions.

Main Methods:

• Utilized HEK293 reporter cell lines expressing human or murine NOD2 receptors to assess Chlamydia-induced signaling.
• Investigated the role of the chlamydial amidase enzyme (AmiA_CT) and inhibitors of PG/LPS biosynthesis on NOD2 signaling.
• Examined the impact of NOD2 ligand pre-treatment on chlamydial inclusion size.

Main Results:

• Chlamydia-induced NOD2 signaling occurs later in the pathogen's developmental cycle compared to NOD1 signaling.
• NOD2 signaling is modulated by disrupting AmiA_CT or inducing lysis of reticulate bodies (RB) via PG/LPS biosynthesis inhibitors.
• Pre-treatment with NOD2-stimulatory ligands reduced chlamydial inclusion size.

Conclusions:

• Chlamydia-induced NOD2 signaling likely results from RB lytic events during the reticulate body to elementary body (RB to EB) transition.
• Chlamydia may preferentially degrade its PG during development to minimize NOD2 ligand generation, potentially at the expense of increased NOD1 signaling.
• Understanding these immune evasion strategies is crucial for developing effective therapeutic interventions against chlamydial infections.