Protease inhibitors decrease IgG shedding from Staphylococcus aureus, increasing complement activation and...

Area of Science:

• Immunology
• Microbiology
• Biochemistry

Background:

• Staphylococcus aureus is a significant human pathogen.
• Humoral immunity, involving antibodies (IgG) and complement, is crucial for controlling S. aureus infections.
• S. aureus employs mechanisms to evade host defenses.

Purpose of the Study:

• To investigate the hypothesis that S. aureus cleaves surface-bound IgG, thereby inhibiting opsonophagocytosis.
• To identify the staphylococcal proteases responsible for IgG cleavage.
• To determine if preventing IgG cleavage enhances complement deposition and neutrophil-mediated phagocytosis.

Main Methods:

• Coating S. aureus with purified human IgG.
• Assaying for cleaved IgG fragments using ELISA and Western blot.
• Utilizing protease inhibitors (broad-spectrum, serine, cysteine, metalloprotease) to assess their effect on IgG cleavage.
• Measuring complement C3 fragment deposition, neutrophil association, and phagocytosis.

Main Results:

• S. aureus efficiently shed surface-bound IgG in vitro.
• Broad-spectrum protease inhibitors blocked IgG cleavage, implicating staphylococcal proteases.
• Serine and cysteine protease inhibitors reduced IgG cleavage, while metalloprotease inhibitors had no effect.
• Inhibiting IgG cleavage increased complement C3 fragment deposition and enhanced neutrophil association and phagocytosis.

Conclusions:

• Staphylococcus aureus utilizes proteases to cleave bound IgG, a mechanism for evading humoral immune defenses.
• Blocking this IgG cleavage enhances complement deposition and promotes neutrophil phagocytosis, suggesting a therapeutic target.