Antigen Presenting Cells and T Cell Activation

Key Concepts

• Professional Antigen Presenting Cells (APCs)
  • Express both MHC Class II molecules and co-stimulator molecules such as CD80

CD4 T Cell Activation

• Stimulation Process
  • Involves interaction of T-Cell Receptor (TCR) and co-receptor molecules with MHC peptide complex
  • Interaction between CD80 on APC and CD28 on T-Cell
• Bidirectional Signaling
  • Signals APC to express additional co-stimulatory molecules (CD86, CD40)
  • Induces T-Cell to express CD40 ligand (CD40L)
• Full Activation
  • Interaction between CD40L (T-Cell) and CD40 (APC)
  • Additional stimulation through CD28-CD86 interaction

CD8 T Cell Activation

• Multiple Receptor-Ligand Interactions
  • APC expresses co-stimulatory molecules such as 41BB ligand (41BBL)
• Activation Signals
  • Initial activation induces CD8 T-Cells to express 41BB
  • Binding of 41BB ligand to 41BB is required for full activation of CD8 T-Cells