Question

Opsonin is

• A. C3a
• B. C3b
• C. C5a
• D. C6

Answer 1

The Correct Option is B

Opsonins are molecules that enhance phagocytosis by marking an antigen for an immune response, usually by coating the surface of the pathogen. This process aids the immune system in identifying and attacking foreign invaders.

In the context of the complement system, C3b functions as a powerful opsonin. Once a pathogen is coated with C3b, phagocytes such as macrophages and neutrophils can more readily identify, bind to, and ingest the pathogen. This process is a crucial part of the immune response, facilitating the clearance of pathogens from the body.

Let's briefly analyze the given options:

• C3a: This is an anaphylatoxin that aids in inflammation and immune response but does not have opsonic properties.
• C3b: This is an opsonin, playing a crucial role in tagging pathogens for phagocytosis.
• C5a: Similar to C3a, this is also an anaphylatoxin but not an opsonin.
• C6: Part of the membrane attack complex, C6 is not involved in opsonization.

Therefore, the correct answer is C3b.