Question:
The innate pathways for the activation of complement system include
A. Classical pathway
B. Alternative pathway
C. Lectin pathway
D. TLR pathway
Choose the correct answer from the options given below:
The innate pathways for the activation of complement system include
A. Classical pathway
B. Alternative pathway
C. Lectin pathway
D. TLR pathway
Choose the correct answer from the options given below:
A. Classical pathway
B. Alternative pathway
C. Lectin pathway
D. TLR pathway
Choose the correct answer from the options given below:
Show Hint
The alternative and lectin pathways are antibody-independent (innate), while the classical pathway is antibody-dependent (adaptive, linked to IgG/IgM). TLRs are cellular receptors, not complement components.
Updated On: Aug 13, 2026
- A and B only
- B and C only
- A, B and C only
- A, B and D only
Show Solution
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The complement system is a biochemical cascade composed of plasma proteins that assist the immune system.
It can be activated through three distinct enzymatic pathways: classical, alternative, and lectin.
The classification into innate and adaptive mechanisms depends on whether the pathway requires antigen-specific antibodies for its initiation.
Detailed Explanation:
Let let us examine the activation mechanisms of each option:
- A. Classical pathway: Initiated by the binding of C1q to antigen-antibody complexes (IgG or IgM). Because it typically requires specific antibodies, it is considered an effector mechanism of the adaptive immune system.
- B. Alternative pathway: Activated spontaneously by the slow hydrolysis of C3 and direct deposition of C3b onto foreign cell surfaces. It does not require antibodies and functions entirely as an innate immune defense.
- C. Lectin pathway: Initiated when mannose-binding lectin (MBL) or ficolins bind to specific carbohydrate patterns (like mannose) on microbial cell walls. This pathway is antibody-independent and operates in the innate immune response.
- D. TLR pathway: Toll-Like Receptors (TLRs) are cellular pattern recognition receptors. They activate intracellular signaling cascades to induce cytokine production but do not directly activate the extracellular plasma complement cascade.
Thus, the innate pathways of complement activation are the Alternative (B) and Lectin (C) pathways.
Step 2: Final Answer:
The correct choice is B and C only, corresponding to Option (B).
The complement system is a biochemical cascade composed of plasma proteins that assist the immune system.
It can be activated through three distinct enzymatic pathways: classical, alternative, and lectin.
The classification into innate and adaptive mechanisms depends on whether the pathway requires antigen-specific antibodies for its initiation.
Detailed Explanation:
Let let us examine the activation mechanisms of each option:
- A. Classical pathway: Initiated by the binding of C1q to antigen-antibody complexes (IgG or IgM). Because it typically requires specific antibodies, it is considered an effector mechanism of the adaptive immune system.
- B. Alternative pathway: Activated spontaneously by the slow hydrolysis of C3 and direct deposition of C3b onto foreign cell surfaces. It does not require antibodies and functions entirely as an innate immune defense.
- C. Lectin pathway: Initiated when mannose-binding lectin (MBL) or ficolins bind to specific carbohydrate patterns (like mannose) on microbial cell walls. This pathway is antibody-independent and operates in the innate immune response.
- D. TLR pathway: Toll-Like Receptors (TLRs) are cellular pattern recognition receptors. They activate intracellular signaling cascades to induce cytokine production but do not directly activate the extracellular plasma complement cascade.
Thus, the innate pathways of complement activation are the Alternative (B) and Lectin (C) pathways.
Step 2: Final Answer:
The correct choice is B and C only, corresponding to Option (B).
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