Question

Consider the following and choose the correct answer Assertion [A]: MHC Class I presents endogenous antigens to CD8\(^+\) T cells. Reason [R]: Endogenous peptides are generated in lysosomes. The correct answer is

• A. Both [A] and [R] are true and [R] is the correct explanation of [A]
• B. Both [A] and [R] are true and [R] is not the correct explanation of [A]
• C. [A] is true, but [R] is false
• D. [A] is false, but [R] is true

Hint:

Antigen processing pathways: \[ \boxed{ \begin{aligned} \text{MHC Class I} &\rightarrow \text{Proteasome} \rightarrow \text{CD8}^{+}\text{ T cells} \text{MHC Class II} &\rightarrow \text{Lysosome} \rightarrow \text{CD4}^{+}\text{ T cells} \end{aligned} } \]

Answer 1

The Correct Option is C

Step 1: Examine the assertion. MHC Class I molecules present endogenous (intracellular) peptides to \[ \boxed{\text{CD8}^{+}\text{ cytotoxic T lymphocytes}.} \] Hence, \[ \boxed{\text{Assertion [A] is true}.} \]

Step 2: Examine the reason. Endogenous peptides are generated mainly by \[ \boxed{\text{Proteasomal degradation in the cytoplasm},} \] not in lysosomes. Lysosomes generate peptides for the MHC Class II pathway. Therefore, \[ \boxed{\text{Reason [R] is false}.} \] Thus, \[ \boxed{(C)} \] is the correct answer.