Question

Given below are two statements :
one is labelled as
Assertion (A) and the other is labelled as
Reason (R).
Assertion (A) :
IgG is the first immunoglobulin produced during a primary immune response.
Reason (R) :
IgM has a pentameric structure that allows efficient activation of the complement system.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Remember:
• IgM \(\rightarrow\) First antibody in primary response
• IgG \(\rightarrow\) Most abundant antibody in secondary response \[ \text{IgM pentamer} \Rightarrow \text{Efficient complement activation} \]

Answer 1

The Correct Option is D

Concept: During an immune response, B-lymphocytes produce different classes of immunoglobulins (antibodies). In a primary immune response: \[ \text{IgM is the first antibody produced} \] Later, class switching occurs and other immunoglobulins such as IgG are produced. IgM exists mainly as a: \[ \text{Pentamer} \] which makes it highly efficient in activating the complement system.

Step 1: Evaluating Assertion (A). The assertion states: \[ \text{IgG is the first immunoglobulin produced during primary immune response} \] This statement is incorrect because: \[ \boxed{\text{IgM is the first antibody produced in primary immune response}} \] IgG appears later after class switching. Therefore: \[ \boxed{(A) \text{ is incorrect}} \]

Step 2: Evaluating Reason (R). The reason states: \[ \text{IgM has a pentameric structure allowing efficient complement activation} \] This statement is correct. Because of its pentameric structure:
• IgM has high avidity
• IgM efficiently activates the classical complement pathway Thus: \[ \boxed{(R) \text{ is correct}} \]

Step 3: Selecting the correct option. Since: \[ (A) \text{ is false and } (R) \text{ is true} \] the correct answer is: \[ \boxed{(D)\ (A)\text{ is not correct but }(R)\text{ is correct}} \]