Intracellular bacteria recognition contributes to maximal interleukin (IL)-12 production by IL-10-deficient...

Area of Science:

• Immunology
• Gastroenterology
• Microbiology

Background:

• Interleukin-12 (IL-12) is crucial for T helper cell type 1 immunity and inflammatory diseases.
• In Interleukin-10 knock-out (IL-10 KO) mice, IL-12 triggers intestinal inflammation, with macrophages producing abundant IL-12 in response to commensal bacteria.
• Intact bacteria are more potent inducers of macrophage IL-12 production than their components, suggesting a role for intracellular recognition mechanisms.

Purpose of the Study:

• To investigate the role of intracellular recognition mechanisms in IL-12 induction.
• To elucidate the signaling pathways involved in excessive IL-12 production by macrophages in IL-10 KO mice stimulated with enteric bacteria.

Main Methods:

• Utilized IL-10 KO mouse bone marrow-derived (BM) macrophages stimulated with Escherichia coli.
• Assessed IL-12p70 production, phagocytosis inhibition (cytochalasin D), protein synthesis inhibition (cycloheximide), and signal transducer and activator of transcription 1 (STAT1) activation.
• Analyzed induction of Interferon regulatory factors-1 and -8 (IRF-1, IRF-8).

Main Results:

• Escherichia coli stimulation induced significantly higher IL-12p70 production in IL-10 KO BM macrophages compared to LPS + Interferon (IFN)-γ.
• Phagocytosis and de novo protein synthesis were essential for IL-12 production, as shown by inhibition with cytochalasin D and cycloheximide.
• STAT1 activation and induction of IRF-1 and IRF-8, downstream of STAT1, were mediated by phagocytosis, even in the absence of detectable IFN-γ.

Conclusions:

• Enteric bacteria stimulate excessive IL-12p70 production in IL-10 KO BM macrophages through phagocytosis-dependent signaling.
• STAT1 signaling plays a critical role in this process, independent of IFN-γ, highlighting non-canonical pathways in IL-12 hyper-production.
• These findings shed light on mechanisms underlying intestinal inflammation in IL-10 deficient models.