PD-1 suppresses protective immunity to Streptococcus pneumoniae through a B cell-intrinsic mechanism

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• The programmed cell death 1 (PD-1) and its ligands (PD-L) pathway is a key regulator of immune responses.
• Its role in bacterial infections, particularly extracellular bacterial infections, remains largely unexplored.

Purpose of the Study:

• To investigate the role of the PD-1:PD-L pathway in host defense against Streptococcus pneumoniae infection.
• To determine if targeting PD-1 can enhance protective immunity against pneumococcal infections.

Main Methods:

• Utilized PD-1 knockout mice and PD-1 blocking antibodies in a mouse model of Streptococcus pneumoniae infection.
• Assessed B cell proliferation, isotype switching, and IgG production in response to pneumococcal antigens.
• Investigated the B cell-intrinsic role of PD-1 expression.

Main Results:

• Disruption of PD-1:PD-L interactions significantly increased survival against lethal S. pneumoniae infection.
• Enhanced survival was associated with increased proliferation, isotype switching, and IgG production by B cells specific for pneumococcal capsule.
• PD-1 was found to be induced on B cells and suppressed IgG production and protection in a B cell-intrinsic manner.

Conclusions:

• B cell-expressed PD-1 plays a critical role in regulating host defense against Streptococcus pneumoniae.
• The PD-1:PD-L pathway, particularly through B7-H1 and B7-DC, suppresses protective IgG responses to pneumococcal infection.
• Targeting B cell-intrinsic PD-1 represents a potential strategy for enhancing immunity against encapsulated bacteria.