CD14 facilitates invasive respiratory tract infection by Streptococcus pneumoniae

Area of Science:

• Immunology
• Microbiology
• Respiratory Medicine

Background:

• CD14 (cluster of differentiation 14) is a pattern recognition receptor crucial for recognizing bacterial ligands, particularly lipopolysaccharide in Gram-negative infections.
• Its role in host defense against Gram-positive bacterial infections, like Streptococcus pneumoniae, remains incompletely understood.

Purpose of the Study:

• To investigate the specific role of CD14 in the pathogenesis of Gram-positive bacterial pneumonia caused by Streptococcus pneumoniae.
• To determine if CD14 contributes to the development of invasive pneumococcal disease.

Main Methods:

• Utilized CD14 knockout (KO) and wild-type (WT) mice models for intranasal infection with Streptococcus pneumoniae.
• Assessed outcomes including lethality, bacterial load in lung homogenates and bronchoalveolar lavage fluid, blood cultures, and lung inflammation markers (histopathology, cytokines, chemokines).
• Administered recombinant soluble CD14 to KO mice to evaluate its sufficiency in restoring susceptibility.

Main Results:

• CD14 KO mice exhibited significantly reduced lethality and a >10-fold lower bacterial load in lung homogenates compared to WT mice.
• WT mice developed bacteremia and systemic infection, while CD14 KO mice did not, indicating CD14's role in systemic spread.
• Lung inflammation was attenuated in CD14 KO mice.
• Reintroduction of soluble CD14 into KO mice restored susceptibility to S. pneumoniae, leading to increased bacterial load and bacteremia.

Conclusions:

• Soluble CD14 in the bronchoalveolar space is essential for Streptococcus pneumoniae to establish invasive respiratory tract infections.
• CD14 acts as a critical factor enabling pneumococcal bacteria to cause invasive disease, highlighting it as a potential therapeutic target.