Lung-resident memory B cells protect against bacterial pneumonia

Area of Science:

• Immunology
• Pulmonary Medicine
• Microbiology

Background:

• Lung-resident memory B cells (BRM cells) are known after influenza infections but their role in immunity against other pathogens is unclear.
• The functional significance of BRM cells in lung immunity requires further investigation.
• Understanding BRM cell presence and function is key to developing new strategies against respiratory infections.

Purpose of the Study:

• To determine if BRM cells are elicited by Streptococcus pneumoniae, a common respiratory pathogen.
• To investigate the presence of BRM cells in human lungs.
• To assess the importance of BRM cells in defending against pneumococcal pneumonia.

Main Methods:

• Mice were infected with S. pneumoniae and lungs were analyzed for B cell populations post-recovery.
• B cells from mouse and human lungs were characterized for resident memory phenotypes and surface markers (CD69, PD-L2, CD80, CD73).
• In vivo depletion of PD-L2+ B cells in mice was performed to evaluate their role in bacterial clearance and antibody production.

Main Results:

• Mouse lungs after pneumococcal infection contained plasma cells and noncirculating memory B cells with resident memory markers, but not organized tertiary lymphoid organs.
• Human lungs also exhibited B cells with a resident memory phenotype.
• Depletion of PD-L2+ B cells, including BRM cells, in mice led to reduced bacterial clearance and lower levels of pneumococcus-reactive antibodies in the lungs.

Conclusions:

• Lung-resident memory B cells are a common feature of pathogen-experienced lungs, elicited by pneumococcal infections.
• These BRM cells play a significant role in pulmonary antibacterial immunity.
• The findings highlight BRM cells as a critical component of the lung's immune defense against bacterial pathogens.