Before T cells become activated, they require an antigen encounter. Naive T cells are shown to express L-selectin which aids in binding to high endothelial cells expressing L-selectin ligand in regions where they are most likely to encounter an antigen. In which of the following locations are these high endothelial cells most likely to be located?

• A. Bone marrow.
• B. Capillaries.
• C. Lymph nodes.
• D. Heart.

Answer: (C)

Verified step by step guidance

1. Understand that naive T cells need to encounter antigens to become activated. This encounter is facilitated by their movement to specific locations in the body.
2. Recognize that L-selectin is a molecule expressed on naive T cells that helps them bind to high endothelial venules (HEVs).
3. High endothelial venules are specialized blood vessels that are primarily found in lymphoid tissues, which are key sites for immune cell interactions.
4. Consider the role of lymph nodes in the immune system. They are strategically located throughout the body to filter lymph fluid and provide a site for immune cells to encounter antigens.
5. Conclude that lymph nodes are the most likely location for high endothelial cells expressing L-selectin ligand, as they facilitate the entry of naive T cells into the lymph node where antigen presentation occurs.