Which of the following components can act as an opsonin?
A) C1q
B) C3b
C) C4a
D) C5b

Question

Quizplus · Accepted Answer

C3b and C4b can both act as opsonins, binding directly to the surface of the microbe to enhance phagocytosis. Phagocytes have complement receptors on the cell surface that bind to C3b or C4b for a tighter bond prior to phagocytosis. C1q is the first component of the classical pathway and binds to antibodies on the surface of a pathogen, but does not enhance phagocytosis. C4a and the other smaller components from cleavage of inactive components act as chemoattractants, but not as opsonins. C5b serves as the anchor to begin formation of the MAC pore complex, and does not function as an opsonin.

Which of the Following Components Can Act as an Opsonin