Gut microbial dysbiosis activates the classical complement pathway in a short-term morphine treatment model

Area of Science:

• Immunology
• Microbiology
• Gastroenterology

Background:

• Intestinal homeostasis relies on antibodies and a microbiome-dependent complement system.
• Morphine rapidly induces gut microbial dysbiosis, favoring pathogenic bacteria over commensals.

Purpose of the Study:

• To investigate early immune responses in the gut following short-term morphine administration.
• To elucidate the role of the microbiome in morphine-induced immune activation.

Main Methods:

• Utilized a murine model of short-term morphine treatment.
• Analyzed gene expression of classical complement pathway components.
• Quantified complement proteins (C1q, C3) and antibodies (IgM, IgG) in ileal luminal content.
• Assessed neutrophil infiltration and activation.
• Investigated microbiome dependence by comparing results with and without microbial depletion.

Main Results:

• Morphine treatment upregulated classical complement pathway genes within 24 hours.
• Increased levels of complement proteins C1q and C3, and complement-activating antibodies IgM and IgG were observed in the ileum.
• These increases were dependent on the microbiome; microbial depletion prevented them.
• Neutrophil infiltration and activation occurred concurrently with microbial dysbiosis.

Conclusions:

• Demonstrates rapid, microbiome-dependent recruitment of complement system components to the intestine during morphine-induced dysbiosis.
• Highlights the classical complement system's activation as a protective host response against microbial dysbiosis.
• Confirms the intricate relationship between the gut microbiome and the intestinal complement system.