IMMUNOLOGY

IMMUNOGLOBULINS

COMPLEMENT SYSTEM

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Which complement protein initiates phagocytosis by binding to CR1 on macrophages?
A
C3a
B
C3b
C
C5a
D
C5b
Explanation: 

Detailed explanation-1: -CR1 binds C3b and C4b, thereby mediating phagocytosis by neutrophils and monocytes. RBC CR1 is important in the processing of immune complexes, binding them for transport to the liver and spleen for removal from the circulation.

Detailed explanation-2: -The C5a complement system can be activated through three pathways: classical (CP), lectin (LP), and alternative (AP). CP begins with antibody-mediated activation of C1 complex, which leads to formation of the C4bC2a complex, the C3 convertase.

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