Question:
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Mouse IgD is susceptible to destruction by protease in serum and hence, cannot be detected in serum
Reason R: Mouse IgD has got short hinge region and no inter chain disulfide bonds
In light of the above statements, choose the correct answer from the options given below:
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Mouse IgD is susceptible to destruction by protease in serum and hence, cannot be detected in serum
Reason R: Mouse IgD has got short hinge region and no inter chain disulfide bonds
In light of the above statements, choose the correct answer from the options given below:
Assertion A: Mouse IgD is susceptible to destruction by protease in serum and hence, cannot be detected in serum
Reason R: Mouse IgD has got short hinge region and no inter chain disulfide bonds
In light of the above statements, choose the correct answer from the options given below:
Show Hint
Mouse IgD is highly susceptible to serum proteases and is difficult to detect in serum because it lacks interchain disulfide bonds between its heavy chains, reducing its structural stability.
Updated On: Aug 13, 2026
- Both A and R are true and R is the correct explanation of A
- Both A and R are true but R is NOT the correct explanation of A
- A is true but R is false
- A is false but R is true
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Immunoglobulin D (IgD) is co-expressed with IgM on the surface of mature, naive B cells, serving as a primary antigen receptor.
While IgD is present on the cell membrane, its concentration in the serum of most mammals, particularly mice, is extremely low.
Detailed Explanation:
Let us evaluate both statements:
- Assertion A: In mice, IgD is highly unstable in fluid environments and is barely detectable in serum. It is rapidly degraded by serum proteases soon after secretion, making direct serological detection difficult. Thus, Assertion A is true.
- Reason R: The structural basis for this high susceptibility to proteolysis lies in the unique molecular architecture of mouse IgD. Unlike human IgD, which features a long hinge region, mouse IgD has a deleted $C_H2$ domain, resulting in an unstable, short hinge region. Crucially, mouse IgD lacks the interchain disulfide bonds that covalently link the two heavy chains in other immunoglobulin classes. This lack of covalent stabilization makes the molecule flexible but structurally unstable, exposing it to rapid cleavage by proteolytic enzymes in the serum. Thus, Reason R is true and provides the direct structural explanation for Assertion A.
Step 2: Final Answer:
Both A and R are true, and R is the correct explanation of A.
Immunoglobulin D (IgD) is co-expressed with IgM on the surface of mature, naive B cells, serving as a primary antigen receptor.
While IgD is present on the cell membrane, its concentration in the serum of most mammals, particularly mice, is extremely low.
Detailed Explanation:
Let us evaluate both statements:
- Assertion A: In mice, IgD is highly unstable in fluid environments and is barely detectable in serum. It is rapidly degraded by serum proteases soon after secretion, making direct serological detection difficult. Thus, Assertion A is true.
- Reason R: The structural basis for this high susceptibility to proteolysis lies in the unique molecular architecture of mouse IgD. Unlike human IgD, which features a long hinge region, mouse IgD has a deleted $C_H2$ domain, resulting in an unstable, short hinge region. Crucially, mouse IgD lacks the interchain disulfide bonds that covalently link the two heavy chains in other immunoglobulin classes. This lack of covalent stabilization makes the molecule flexible but structurally unstable, exposing it to rapid cleavage by proteolytic enzymes in the serum. Thus, Reason R is true and provides the direct structural explanation for Assertion A.
Step 2: Final Answer:
Both A and R are true, and R is the correct explanation of A.
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