Question

Which molecule stabilizes the interaction between T cell receptor and MHC class II?

• A. CD4
• B. CD8
• C. CD28
• D. CD40

Hint:

Use the "Rule of 8" to remember TCR-MHC associations: CD\textbf{4} $\times$ MHC \textbf{II} = 8, and CD\textbf{8} $\times$ MHC \textbf{I} = 8.

Answer 1

The Correct Option is A

The question asks which molecule stabilizes the interaction between the T cell receptor (TCR) and MHC class II molecules. This relates to the immune system, specifically the interaction between T cells and antigen-presenting cells (APCs).

1. Understanding TCR and MHC Class II:
   • The T cell receptor (TCR) is present on the surface of T cells and is responsible for recognizing antigens presented by MHC molecules on the surface of APCs.
   • MHC class II molecules are found on specialized antigen-presenting cells like macrophages, dendritic cells, and B cells. They present exogenous antigens to CD4⁺ T helper cells.
2. Role of CD4 in TCR and MHC Class II Interaction:
   • CD4 is a glycoprotein molecule expressed on the surface of helper T cells (CD4⁺ T cells).
   • CD4 serves as a co-receptor and binds specifically to regions on the MHC class II molecule. This interaction enhances the stability of the binding between the TCR and the antigen-MHC class II complex.
   • Thus, CD4 stabilizes the interaction between the T cell receptor and MHC class II.
3. Exclusion of Other Options:
   • CD8: Located on cytotoxic T cells, CD8 interacts with MHC class I, not class II.
   • CD28: A co-stimulatory molecule that binds with B7 on APCs, playing a role in T cell activation but not in direct stabilization of TCR-MHC class II interaction.
   • CD40: A receptor found on B cells, playing a role in B cell activation and antibody class switching, not directly in TCR-MHC class II interactions.

Thus, the molecule that stabilizes the interaction between the T cell receptor and MHC class II is CD4.