Question

Homing of naive T cells to secondary lymphoid tissues is determined by ___ and ____

Answer 1

Naive T cells are guided to secondary lymphoid tissues by chemokines, which attract them towards the tissues, and adhesion molecules, which mediate their attachment to endothelial cells.

Step-by-step explanation:

The homing of naive T cells to secondary lymphoid tissues is determined by two factors: chemokines and adhesion molecules.

Chemokines:

Chemokines are signaling molecules that are secreted by cells in the secondary lymphoid tissues. They attract naive T cells towards the tissues by binding to chemokine receptors on the surface of T cells. Different chemokines attract T cells to specific secondary lymphoid tissues. For example, CCL19 and CCL21 chemokines attract T cells to lymph nodes.

Adhesion molecules:

Adhesion molecules are proteins that mediate the attachment of T cells to the endothelial cells lining the blood vessels of secondary lymphoid tissues. One well-studied adhesion molecule is L-selectin, which is expressed on naive T cells. L-selectin interacts with adhesion molecules on endothelial cells, allowing T cells to roll and stick to the vessel wall, facilitating their entry into the secondary lymphoid tissues.

Answer 2

The homing of naive T cells to secondary lymphoid tissues is determined by the expression of selectin ligands and chemokine receptors, which facilitate their interaction with antigen-presenting cells. Naive CD4+ T cells bind to MHC II molecules, while naive CD8+ T cells interact with MHC I molecules on APCs, leading to their differentiation into distinct types of effector T cells.

Step-by-step explanation:

The homing of naive T cells to secondary lymphoid tissues is determined by the expression of selectin ligands and chemokine receptors. Naive T cells, which include those that express CD4 or CD8 molecules, leave the thymus and navigate the bloodstream to secondary lymphoid organs like lymph nodes, spleen, and tonsils. Secondary lymphoid organs are where these cells will potentially encounter and respond to antigens presented by antigen-presenting cells (APCs). The interaction of naive T cells with APCs is critical for the activation and differentiation of these cells into effector T cells.

For instance, naive CD4+ T cells interact with APCs through MHC II molecules, whereupon activation, they differentiate into helper T cells that assist in amplifying the immune response. On the other hand, naive CD8+ T cells are prompted by interaction with APCs through MHC I molecules to become cytotoxic T lymphocytes, capable of directly killing infected cells. This process of maturation and differentiation is essential for the body's adaptive immune response and is facilitated by the primary lymphoid organ, which in the case of T cells is the thymus gland.

The coreceptors CD4 and CD8 also serve to enhance the specificity of the interaction between T cells and APCs, which is vital for ensuring an appropriate immune response. In this context, CD4 and CD8 are considered coreceptors because they differentiate whether a T cell receptor (TCR) will engage with an MHC II or MHC I molecule.