Guinea pig neutrophil-macrophage interactions during infection with Mycobacterium tuberculosis

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Mycobacterium tuberculosis (M. tuberculosis) infection poses a significant global health challenge.
• Understanding early host immune responses is crucial for developing effective treatments.
• Neutrophils and macrophages are key immune cells involved in combating bacterial infections.

Purpose of the Study:

• To investigate the role of recombinant guinea pig IL-8 (CXCL8) in neutrophil activation during M. tuberculosis infection.
• To explore the subsequent activation of alveolar macrophages (AM) and their interaction with infected neutrophils.
• To determine the impact of neutrophil-macrophage interactions on intracellular mycobacterial growth.

Main Methods:

• Utilized a Transwell insert culture system for contact-independent co-culture of neutrophils and alveolar macrophages.
• Exposed neutrophils to recombinant guinea pig IL-8 (rgpIL-8) and infected them with M. tuberculosis.
• Measured mRNA expression of IL-1β and TNF-α in AM and assessed neutrophil apoptosis and its effect on AM.

Main Results:

• rgpIL-8-treated, M. tuberculosis-infected neutrophils induced IL-1β and TNF-α mRNA expression in AM.
• TNF-α produced by infected neutrophils was critical for AM activation, while IL-8 had no direct effect.
• M. tuberculosis-infected neutrophils underwent apoptosis, and their phagocytosis by AM upregulated TNF-α and IL-1β mRNA.
• AM that ingested infected, apoptotic neutrophils exhibited suppressed intracellular M. tuberculosis growth.

Conclusions:

• Neutrophil activation by rgpIL-8 contributes to early host defense against M. tuberculosis.
• TNF-α signaling from infected neutrophils plays a vital role in activating alveolar macrophages.
• Neutrophil-macrophage interactions, particularly involving apoptotic neutrophils, are important for controlling M. tuberculosis infection and reducing bacterial burden.