Question

Here are four statements about Major Histocompatibility Complex (MHC).
A. MHC-I is expressed by nearly all nucleated cells
B. MHC-II is expressed by antigen presenting cells and they present antigen to cytotoxic T cells
C. Only Helper T cells and not the cytotoxic T cells can recognize antigen in complex with MHC-II
D. Natural Killer cells express a variety of receptors that engage with MHC-II
Which of the above statement(s) is true?

• A. only B
• B. A and C
• C. A, B and C
• D. A, C and D

Hint:

MHC-I x CD8 = 8. MHC-II x CD4 = 8. (The "Rule of Eight" for T-cell binding).

Answer 1

The Correct Option is B

Step 1: Analysis of MHC-I
MHC-I molecules are indeed found on almost all nucleated cells in the body to present internal antigens to CD8+ T cells (Statement A is true).

Step 2: Analysis of MHC-II
MHC-II is expressed by professional APCs (dendritic cells, macrophages, B cells) but they present to Helper T cells (CD4+), not cytotoxic T cells (Statement B is false).

Step 3: T-cell Recognition
Helper T cells recognize antigens only on MHC-II, while Cytotoxic T cells recognize MHC-I (Statement C is true).

Step 4: Conclusion
Statements A and C are correct. Final Answer: (B)