Opsonins function by coating pathogens to promote phagocytosis. Which molecules act as opsonins?

Opsonins function by coating pathogens to promote phagocytosis. Which molecules act as opsonins?

• A. IgG and C3b
• B. C3a and C5a
• C. IgA and IgM
• D. IgE and C4b

Answer: (A)

Opsonization marks pathogens for phagocytosis, providing a handle for phagocytes to grab onto and engulf the invader. The best-known opsonins are IgG antibodies and the C3b fragment of complement. IgG coats microbes via its antigen-binding region and then is recognized by Fc gamma receptors on macrophages and neutrophils, which stimulates phagocytosis. C3b binds to the surface of the microbe as part of the complement cascade and is recognized by complement receptors (such as CR1) on phagocytes, also promoting engulfment. The inflammatory peptides C3a and C5a drive inflammation rather than tagging pathogens for uptake. IgA and IgM have roles in immune defense, but IgG is the primary antibody that acts as an opsonin for phagocytosis in this context, with C3b providing the complement-mediated opsonization mechanism.

Opsonization marks pathogens for phagocytosis, providing a handle for phagocytes to grab onto and engulf the invader. The best-known opsonins are IgG antibodies and the C3b fragment of complement. IgG coats microbes via its antigen-binding region and then is recognized by Fc gamma receptors on macrophages and neutrophils, which stimulates phagocytosis. C3b binds to the surface of the microbe as part of the complement cascade and is recognized by complement receptors (such as CR1) on phagocytes, also promoting engulfment. The inflammatory peptides C3a and C5a drive inflammation rather than tagging pathogens for uptake. IgA and IgM have roles in immune defense, but IgG is the primary antibody that acts as an opsonin for phagocytosis in this context, with C3b providing the complement-mediated opsonization mechanism.