Describe the route that a Peyer's patch-activated T lymphocyte follows, beginning with a naive T lymphocyte in a high endothelial venule and ending with an effector T lymphocyte in the lamina propria

Question

What will be an ideal response?

Answer 1

The chemokines CCL21 and CCL19 synthesized in Peyer's patches bind to CCR7 on naive T cells and recruit them into the lymphoid tissue across a high endothelial venule. The T cells bearing appropriate antigen-specific receptors are stimulated by dendritic cells and undergo proliferation and differentiation within the Peyer's patches. Activated T cells then leave the Peyer's patch and enter the lymph, and travel through mesenteric lymph nodes before arriving via the lymph at the thoracic duct and then enter the bloodstream. From the bloodstream, activated T cells home only to mucosa-associated lymphoid tissue because during their differentiation they cease to express CCR7 and L-selectin, which are otherwise required to enter systemic lymphoid tissues. Instead, they now express α4:β7, which binds to MAdCAM-1 on gut-associated endothelia and CCR9, the chemokine receptor for CCL25, which is synthesized in the lamina propria. They cross the vascular endothelium into the lamina propria (some subsequently entering the epithelium), where they secrete cytokines and mediate killing.