Naive T-Lymphocytes and Lymphoid Organs

High Endothelial Venules (HEV)

• Specialized endothelial walls of blood vessels in T-cell areas of lymphoid organs.
• Facilitate the exit of naive T-lymphocytes from the bloodstream.

Molecules Involved in Lymphocyte Homing

• GlyCAM-1: Homing receptor.
• ICAM-1: Adhesion molecule.
• Chemokines (e.g., MIP-3β).

Binding and Migration Process

1. Initial Binding
   • Mediated by L-selectin binding to GlyCAM-1.
2. Tight Adhesion
   • Triggered by chemokines on the extracellular matrix.
   • Integrin LFA-1 binds tightly to its ligand ICAM-1.
3. Migration
   • Lymphocyte migrates across the endothelium into the T-cell area of the lymph node.

Inspection for Antigen

• Naive T-cell inspects dendritic cells in the lymph node for its specific antigen.
• No Antigen Recognized: T-cell is not activated, exits the lymph node, returns to circulation.
• Antigen Recognized: T-cell is activated, begins to proliferate and mature into effector cells.

Post-Activation

• Activated T-cells (effector cells) leave the lymph node after a few days.
• Return to circulation to perform their immune function.