In opsonization with IgG, why would it be important that IgG react with the antigen BEFORE a phagocytic cell recognizes the antibody molecule?

• A. If the IgG is bound to the phagocyte before opsonization, it would most likely be ingested by the phagocyte before it could bind to a pathogen.
• B. Binding of IgG by phagocytes would block the antigen binding sites on the IgG molecules, preventing them from binding to the microbes.
• C. Binding of IgG by phagocytes changes the conformation of the antibody's antigen binding site making it less effective at binding the correct foreign antigen.
• D. Binding of an antibody by phagocytes results in immediate release of damaging hydrolytic enzymes to the outside of the cell which would destroy all remaining antibodies.

Answer: (A)

Verified step by step guidance

1. Understand the role of IgG in opsonization: IgG is an antibody that binds to antigens on the surface of pathogens, marking them for destruction by phagocytes.
2. Recognize the importance of sequence: IgG must bind to the antigen before the phagocyte can recognize and bind to the IgG. This sequence ensures that the pathogen is effectively marked for phagocytosis.
3. Consider the consequences of premature binding: If IgG binds to the phagocyte before it binds to the antigen, the phagocyte may ingest the IgG without it being attached to a pathogen, thus failing to target the pathogen.
4. Analyze the impact on antigen binding sites: Binding of IgG to phagocytes before antigen binding can block the antigen binding sites, preventing IgG from attaching to the pathogen.
5. Evaluate the structural changes: Binding of IgG to phagocytes can alter the conformation of the antibody's antigen binding site, reducing its ability to bind to the correct antigen and potentially leading to the release of damaging enzymes.