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Stimulation of the intracellular killing of Staphylococcus aureus by monocytes: regulation by immunoglobulin G and
Abstract:
The intracellular killing of Staphylococcus aureus by human monocytes requires continuous stimulation by extracellular serum factors interacting with the cells via membrane binding sites. At least 75% of the intracellular killing in the presence of fresh serum was accounted for by the combined stimulatory activities of IgG, C3/C3b, and B/Bb. C3b is a more potent stimulator than C3, and Bb stimulates the killing to the same degree as B. The stimulation of intracellular killing by C3 and C3b occurs by interaction of the stable binding site of this molecule with the C3b receptor in the monocyte membrane. The stimulation of intracellular killing by B and Bb is most probably mediated via a binding site on these proteins interacting with a receptor site in the monocyte membrane. Both complement receptors, i.e., for C3b and B, are pronase sensitive. However, only the C3b receptor can be inhibited by (Fab')2 fragments of anti-C3 receptor antibodies, indicating that the binding sites for C3/C3b and B/bb are different.
Insights
Human monocytes kill Staphylococcus aureus with help from serum factors like IgG and complement proteins (C3/C3b, B/Bb). These factors bind to monocyte receptors, stimulating bacterial killing.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human monocytes are crucial for intracellular killing of Staphylococcus aureus.
- This process relies on stimulation by extracellular serum factors binding to monocyte membrane sites.
Purpose of the Study:
- To identify and characterize the serum factors and their receptors involved in monocyte-mediated intracellular killing of S. aureus.
- To elucidate the mechanisms of stimulation and receptor interactions.
Main Methods:
- Monocyte cell cultures
- Serum factor stimulation assays
- Pronase sensitivity assays
- Inhibition assays using anti-C3 receptor antibodies and (Fab')2 fragments
Main Results:
- IgG, C3/C3b, and B/Bb together account for over 75% of intracellular killing stimulation.
- C3b is a more potent stimulator than C3; Bb stimulates killing similarly to B.
- Stimulation by C3/C3b involves binding to the C3b receptor, while B/Bb likely interact with a distinct receptor.
- Both complement receptors are pronase sensitive, but only the C3b receptor is inhibited by anti-C3 receptor antibodies.
Conclusions:
- Multiple serum factors, including IgG and complement components (C3/C3b, B/Bb), are essential for effective S. aureus intracellular killing by monocytes.
- Distinct membrane receptors mediate the stimulatory effects of C3/C3b and B/Bb on monocyte bactericidal activity.
- Understanding these interactions is key to developing strategies against S. aureus infections.