Question

Class I MHC molecules present peptides to which of the following cell type?

• A. CD8+ cytotoxic T-cells
• B. CD4+ T-helper cells
• C. Dendritic cells
• D. Macrophages

Hint:

Use the "rule of 8" to remember the MHC-T cell interactions:

MHC Class \textbf{I} binds to CD\textbf{8} T-cells (\(1 \times 8 = 8\)).
MHC Class \textbf{II} binds to CD\textbf{4} T-cells (\(2 \times 4 = 8\)). \end{itemize}

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Major Histocompatibility Complex (MHC) molecules are cell surface proteins that present antigenic peptides to T-cells. There are two main classes, MHC Class I and MHC Class II, which present peptides to different types of T-cells.

Step 2: Detailed Explanation:
- MHC Class I: These molecules are found on the surface of almost all nucleated cells in the body. Their primary function is to present {endogenous} antigens (peptides from proteins made inside the cell, such as viral proteins or abnormal tumor proteins) to CD8+ cytotoxic T-cells. This interaction signals the cytotoxic T-cell to kill the infected or cancerous cell.
- MHC Class II: These molecules are found only on the surface of professional Antigen-Presenting Cells (APCs), such as dendritic cells, macrophages, and B-cells. They present {exogenous} antigens (peptides from pathogens that have been engulfed and broken down) to CD4+ T-helper cells. This interaction helps to activate the T-helper cell, which then orchestrates the broader immune response.

Step 3: Final Answer:
MHC Class I molecules present peptides specifically to CD8+ cytotoxic T-cells. Therefore, option (A) is correct.