Why does Staphylococcus aureus use Protein A to bind IgG antibodies?

• A. To prevent opsonization and phagocytosis by immune cells
• B. To increase antibody-mediated neutralization of toxins
• C. To enhance complement activation and promote inflammation
• D. To facilitate direct lysis of host cells

Answer: (A)

Verified step by step guidance

1. Understand the role of Protein A in Staphylococcus aureus: Protein A is a surface protein that binds to the Fc region of IgG antibodies.
2. Recall the structure of an antibody: IgG antibodies have two main regions - the Fab region that binds antigens, and the Fc region that interacts with immune cells.
3. Recognize that by binding the Fc region of IgG, Protein A disrupts the normal orientation of antibodies on the bacterial surface, preventing immune cells from recognizing and binding to the bacteria effectively.
4. This interference inhibits opsonization, a process where antibodies mark pathogens for phagocytosis by immune cells such as macrophages and neutrophils.
5. Therefore, Protein A helps Staphylococcus aureus evade the immune system by preventing opsonization and subsequent phagocytosis, enhancing bacterial survival.