If the following are placed in the order of occurrence, which would be the third step?
a. Activation of C5 through C9
b. Cell lysis
c. Antigen–antibody reaction
d. Activation of C3
e. Activation of C2 through C4

검증된 단계별 안내

Identify the sequence of events in the classical complement pathway, which is triggered by the antigen–antibody reaction.

Recognize that the first step is the antigen–antibody reaction (option c), where antibodies bind to antigens to initiate the complement cascade.

Next, understand that activation of complement components C2 through C4 (option e) follows, forming the C3 convertase enzyme complex.

Then, the activation of C3 (option d) occurs, which is a critical amplification step in the pathway.

After C3 activation, the terminal components C5 through C9 (option a) are activated, leading to the formation of the membrane attack complex and resulting in cell lysis (option b).

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주요 개념

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Complement System Activation Pathway

The complement system is a series of proteins that enhance immune responses. Activation begins with antigen–antibody complexes triggering a cascade involving complement proteins C1 through C9, leading to pathogen elimination.

Role of Complement Components C2, C3, C4, and C5-C9

Complement proteins C2, C3, and C4 are activated early in the cascade to form complexes that amplify the response. Activation of C5 through C9 forms the membrane attack complex (MAC), which directly causes cell lysis.

Sequence of Events in Complement-Mediated Cell Lysis

The sequence starts with antigen–antibody reaction, followed by activation of early complement proteins (C2-C4), then C3 activation, leading to activation of C5-C9, and finally cell lysis by the MAC disrupting the target cell membrane.

If the following are placed in the order of occurrence, which would be the third step?a. Activation of C5 through C9b. Cell lysisc. Antigen–antibody reactiond. Activation of C3e. Activation of C2 through C4