Question

You are performing research on CCR7 and the roles it plays in T cell homing in humans. To begin your research, you use public websites to identify which tissue expresses the ligand CCL21 in humans. You find one tissue that exhibits several log fold higher expression than others, it is the:

a. Thymus

b. Lymph node

c. Blood

d. Skin

Answer 1

CCL2, thymus derived chemokine, is a secondary lymphoid chemokine. It is produced by high endothelial venules and lymphoid endothelial cells. It is produced by stromal cells present in T cell zones of secondary lymphoid organs. Its receptor is CCR7, a G-protein coupled receptor. CCL21 is present on surface of dendritic cells of lymph node. CCL21 recruits APC dendritic cells and naïve t cell that express CCR7 to lymph node.

CCL21 is involved in expansion of CD4⁺ and CD8⁺ T cells. It also induces Th1 polarization. Skin is not a lymphoid organ but involved in innate immune responses. Blood doesn’t express CCL21. Thymus is a primary lymphoid organ.

Right choice: b. Lymph node