Question at position 10 Which of the following complement fixation pathways can be initiated by a soluble C3 convertase?All of the answers are correct.AlternativeNone of the answers are correct.LectinClassical单项选择题
A
All of the answers are correct.
B
Alternative
C
None of the answers are correct.
D
Lectin
E
Classical

Question

Question at position 10 Which of the following complement fixation pathways can be initiated by a soluble C3 convertase?All of the answers are correct.AlternativeNone of the answers are correct.LectinClassical单项选择题

A

All of the answers are correct.

B

Alternative

C

None of the answers are correct.

D

Lectin

E

Classical

BlackTom AI · Accepted Answer

The alternative pathway uniquely generates a fluid-phase (soluble) C3 convertase, C3(H2O)Bb, via spontaneous C3 “tick-over.”

1) Relevant knowledge points and concepts
- Three complement activation pathways: classical, lectin, and alternative.  
- Each pathway forms a C3 convertase but the composition differs: classical/lectin produce C4b2a (surface-associated), while the alternative pathway produces C3bBb (surface) and a fluid-phase form C3(H2O)Bb.  
- Alternative pathway initiation occurs by spontaneous hydrolysis of C3 (tick-over), recruitment of factor B, cleavage by factor D, and formation of the soluble convertase.

2) Step-by-step reasoning process
- Spontaneous hydrolysis: native C3 ⇢ C3(H2O).  
- C3(H2O) binds factor B: C3(H2O)B.  
- Factor D cleaves bound factor B into Ba and Bb, leaving C3(H2O)Bb — the soluble C3 convertase.  
- C3(H2O)Bb cleaves additional C3 into C3a and C3b. C3b can covalently attach to nearby surfaces, leading to formation of surface-bound C3bBb (amplification loop) stabilized by properdin.

3) Intermediate steps shown
- C3 → spontaneous hydrolysis → C3(H2O)  
- C3(H2O) + factor B → C3(H2O)B  
- Factor D cleaves B → Ba + Bb → C3(H2O)Bb (soluble C3 convertase)  
- C3(H2O)Bb → cleaves C3 → C3a + C3b → opsonization/amplification

4) Why the correct answer is correct
The alternative pathway is the only one that produces this fluid-phase convertase through tick-over; this soluble convertase initiates complement activation without antibody or lectin recognition.

5) Why other options are incorrect
- Classical and Lectin pathways form C3 convertase C4b2a, generated after C1 (classical) or MBL/MASP (lectin) activation, and these are primarily surface-associated rather than produced as a soluble C3(H2O)Bb.  
- “All of the answers” and “None of the answers” are therefore incorrect.

Conclusion: The correct answer is Alternative, which matches the provided answer.

Question at position 10 Which of the following complement fixation pathways can be initiated by a soluble C3 convertase?All of the answers are correct.AlternativeNone of the answers are correct.LectinClassical单项选择题

类似问题

Question at position 51 To which of the following is MBL MOST structurally similar?C5bNone of the answers are correct.BbC1qC3b

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Question at position 20 Which of the following provides serine protease activity in the classical complement activation pathway?Both C1r and C1s act in the classical pathway.C1rMASP-2None of the answers acts in the classical pathway.C1s

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What is the term for a group of proteins in serum that finish off the work of antibodies to destroy bacteria and other cells?

The complement system refers to:

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