Toll-like receptor 9 acts at an early stage in host defence against pneumococcal infection

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Toll-like receptor 9 (TLR9) recognizes prokaryotic DNA and triggers inflammatory responses.
• Previous studies indicated TLR9-deficient mice are more susceptible to viral, but not bacterial infections.

Purpose of the Study:

• To investigate the role of TLR9 in bacterial respiratory tract infections, specifically with Streptococcus pneumoniae.
• To determine if TLR9 deficiency impacts susceptibility to pneumococcal pneumonia.

Main Methods:

• Intranasal challenge studies using Streptococcus pneumoniae in TLR9-deficient mice.
• Assessment of susceptibility in mice deficient in other Toll-like receptors (TLR1, TLR2, TLR4, TLR6) or IL-1R/IL-18R.
• Evaluation of macrophage phagocytic activity and bacterial killing in vitro.

Main Results:

• TLR9-deficient mice exhibited increased susceptibility to Streptococcus pneumoniae respiratory infection.
• TLR9 deficiency impaired early-stage lung infection control before circulating immune cell infiltration.
• Macrophages lacking TLR9 or MyD88 showed reduced pneumococcal uptake and killing capacity.

Conclusions:

• TLR9 plays a critical protective role in the early stages of Streptococcus pneumoniae lung infection.
• TLR9-dependent activation of resident macrophage phagocytosis is essential for early bacterial clearance in the lower respiratory tract.