Staphylococcus aureus-induced plasmacytoid dendritic cell activation is based on an IgG-mediated memory response

Area of Science:

• Immunology
• Microbiology
• Cellular Biology

Background:

• Type I interferons (IFNs) are crucial for antimicrobial defense, enhancing immune responses.
• Plasmacytoid dendritic cells (pDCs) are primary producers of Type I IFN and key innate immune cells.
• Limited knowledge exists on pDC activation by extracellular bacteria.

Purpose of the Study:

• To investigate the mechanism of human pDC activation by Staphylococcus aureus.
• To identify specific bacterial components and host factors involved in pDC response.
• To characterize the nature of pDC activation by extracellular bacteria.

Main Methods:

• Stimulation of human pDCs with Staphylococcus aureus.
• Assessment of IFN-alpha secretion.
• Investigation of the roles of Toll-like receptors (TLRs), bacterial virulence factors, antibodies, and uptake mechanisms.

Main Results:

• Staphylococcus aureus triggers IFN-alpha secretion from human pDCs independently of TLR2.
• The response is specific to coagulase-positive staphylococci and mediated by Ag-specific IgG and CD32.
• Bacterial nucleic acids engaging TLR7/9 after CD32-mediated uptake are implicated.
• Inhibitory DNA oligonucleotides and chloroquine block S. aureus-induced pDC activation.

Conclusions:

• pDC activation by S. aureus is an antigen-specific, antibody-dependent memory response.
• This contrasts with the non-selective TLR2-dependent activation seen in most innate immune cells.
• The findings highlight a unique mechanism of pDC engagement by extracellular bacteria.