Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Major Histocompatibility Complex are of two types which are recognised by the T-Cells
Reason R: Major Histocompatibility Complex differ in their proteins that they display in binding T-cells
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 incorrect
• D. A is incorrect but R is correct

Hint:

Remember the "Rule of 8" for MHC and T cell interactions:
MHC Class I $\times$ CD8 T cell = 8
MHC Class II $\times$ CD4 T cell = 8

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Major Histocompatibility Complex (MHC) is a set of cell-surface proteins essential for the acquired immune system to recognize foreign molecules.
T cells cannot bind directly to free antigens; they can only recognize antigens that are presented on MHC molecules.

Step 2: Detailed Explanation:
Assertion A states that there are two primary classes of MHC molecules recognized by T cells.
This is correct: MHC Class I and MHC Class II are the primary presenting molecules.
Reason R states that these two MHC classes differ in the proteins they display to T cells.
This is also correct and provides the logical explanation for Assertion A:
MHC Class I molecules present endogenous antigens (derived from intracellular proteins or viruses) to CD8+ Cytotoxic T cells.
MHC Class II molecules present exogenous antigens (derived from extracellular pathogens) to CD4+ Helper T cells.
The structural differences in the peptide-binding grooves of MHC Class I and Class II determine which peptides are displayed, ensuring the correct T cell subset is activated.
Therefore, both statements are correct, and Reason R explains the biological basis for the different T cell interactions mentioned in Assertion A.

Step 3: Final Answer:
Both A and R are correct, and R is the correct explanation of A.