Question

Which class of MHC molecules is found on the surface of all nucleated cells?

• A. MHC Class I
• B. MHC Class II
• C. MHC Class III
• D. MHC Class IV

Hint:

MHC I → Present on all nucleated cells → Presents intracellular antigens.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
MHC (Major Histocompatibility Complex) molecules are essential for the immune system to recognize "self" vs "non-self".
Step 2: Detailed Explanation:
MHC Class I: These molecules are expressed on the surface of virtually all nucleated cells in the body. They present internal (endogenous) antigens to $CD8^+$ cytotoxic T-cells. This allows the immune system to monitor if a cell is infected by a virus or has become cancerous.
MHC Class II: These are only found on specialized Antigen-Presenting Cells (APCs) like macrophages, B-cells, and dendritic cells. They present external (exogenous) antigens to $CD4^+$ helper T-cells.
Red blood cells lack a nucleus and therefore do not express MHC Class I.
Step 3: Final Answer:
MHC Class I molecules are found on all nucleated cells.