Question

What is the main role of CD28 in T-cell signaling?

A. Provide costimulation signals
B. Stabilize MHC-peptide-TCR interaction
C. Express MHC class II molecules
D. Suppress T-cell activities

Answer 1

Option (A), CD28's main role is to provide costimulation signals in T-cell signaling, essential for T-cell activation and function.

Step-by-step explanation:

The main role of CD28 in T-cell signaling is to provide costimulation signals. This is crucial for the activation and survival of T cells. Without this costimulatory signal, T cells may become anergic, which means they fail to respond to their specific antigen.

CD28 is a surface protein present on T cells that, upon binding to its ligands CD80 and CD86 on the antigen-presenting cells (APCs), delivers a necessary second signal that, in conjunction with the first signal (the recognition of an antigen by the T-cell receptor or TCR), leads to full T-cell activation.

This is distinct from the role of MHC-peptide-TCR interaction, which provides the specificity to the immune response by ensuring T cells only respond to the correct antigen.