Intracellular pathogen targeting by IL32 elicits cell-autonomous immunity

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Interferon-γ (IFNγ) protects against intracellular pathogens, but downstream defense mechanisms and pathogen evasion strategies remain incompletely understood.
• Host cell defense against vacuolar pathogens like Chlamydia and Encephalitozoon requires elucidation of specific immune surveillance pathways.

Purpose of the Study:

• To identify and characterize a novel immune surveillance and effector circuit involving Interleukin-32 (IL32) against intracellular pathogens.
• To understand the molecular mechanisms by which IL32 targets pathogens and how pathogens evade IL32-mediated defenses.

Main Methods:

• Quantitative proteomics and CRISPR screening identified components of the cysteine/Arg N-degron pathway involved in IL32 modification.
• Forward genetics screen in Chlamydia trachomatis identified pathogen-specific evasion factors.
• Investigated the recruitment of autophagy machinery to pathogen-containing vacuoles.

Main Results:

• Discovered that IL32 targets and restricts diverse vacuolar pathogens, including Chlamydia and Encephalitozoon.
• Uncovered that oxidation-dependent arginylation of IL32 via the N-degron pathway recruits autophagy to pathogen vacuoles.
• Identified Chlamydia's secreted virulence factor IncS as an evasion mechanism that blocks IL32 targeting and prevents xenophagy.

Conclusions:

• Established an IL32-dependent intracellular sensing mechanism linking IFNγ signaling to N-degron-mediated xenophagy.
• Revealed a broadly relevant axis of human host-pathogen conflict involving IL32-mediated defense and pathogen evasion.
• The findings provide insights into host defense against intracellular bacteria and microsporidia.