Lung epithelium and myeloid cells cooperate to clear acute pneumococcal infection

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Streptococcus pneumoniae causes severe infections, particularly in immunocompromised individuals.
• Toll-like receptor (TLR) signaling, mediated by myeloid differentiation factor 88 (MyD88), is vital for immune responses against S. pneumoniae.
• The specific cell types requiring MyD88 for effective immunity remain unclear due to its ubiquitous expression.

Purpose of the Study:

• To investigate the necessity of MyD88 signaling in distinct lung-resident cell populations for protective immunity against S. pneumoniae.
• To elucidate the roles of myeloid and epithelial cell-specific MyD88 signaling in host defense.

Main Methods:

• Utilized novel conditional knockin mouse models to specifically ablate MyD88 signaling in defined cell types.
• Assessed immune responses, including cytokine production, antimicrobial peptide release, neutrophil recruitment, and bacterial clearance, following S. pneumoniae infection.

Main Results:

• MyD88 signaling in lysozyme M (LysM)- and CD11c-expressing myeloid cells is critical for initiating protective immunity.
• MyD88 signaling in pulmonary epithelial cells also plays a vital role in host defense against S. pneumoniae.
• Compartment-specific MyD88 signaling synergistically enhances inflammatory cytokine and antimicrobial peptide production, promoting neutrophil recruitment and bacterial clearance.

Conclusions:

• MyD88 signaling is required in both myeloid and epithelial cells within the lung for effective control of S. pneumoniae infections.
• This study reveals a novel synergistic requirement for compartment-specific MyD88 signaling in orchestrating a protective immune response against pneumococcal pneumonia.