helper T cell extravasation

Definition

Target type: biologicalprocess

The migration of a helper T cell from the blood vessels into the surrounding tissue. A helper T-cell is an effector T cell that provides help in the form of secreted cytokines to other immune cells. [CL:0000912, GOC:BHF]

Helper T cell extravasation is a complex and tightly regulated process by which these cells exit the bloodstream and enter the tissues where they are needed to orchestrate immune responses. This process is essential for immune surveillance and the ability of the immune system to respond to infection and inflammation. It involves a series of steps, each mediated by specific interactions between cell surface molecules and their ligands:

1. **Rolling:** Helper T cells initially slow down and roll along the blood vessel endothelium. This is mediated by selectins, which are expressed on both the T cells and the endothelial cells. L-selectin on the T cell interacts with GlyCAM-1 and CD34 on the endothelial cell, while P-selectin on the endothelium binds to PSGL-1 on the T cell. This rolling interaction allows the T cell to sample the chemokines being produced by the inflamed tissue.
2. **Activation:** The T cell then encounters chemokines (e.g., CCL21, CCL19) that are being produced by the inflamed tissue. These chemokines bind to CCR7 on the T cell surface, triggering a signal transduction cascade that leads to a conformational change in integrins on the T cell.
3. **Adhesion:** The activated integrins on the T cell (LFA-1 and VLA-4) now have a high affinity for their ligands (ICAM-1 and VCAM-1) on the endothelium. This strong adhesion allows the T cell to firmly adhere to the blood vessel wall.
4. **Transmigration:** The final step involves the T cell passing through the endothelial barrier. This occurs via a process known as diapedesis. The T cell squeezes through the junctions between endothelial cells, often assisted by molecules like PECAM-1.
5. **Migration:** Once in the tissue, the T cell follows the chemokine gradient to reach the site of inflammation or infection. Here, the T cell can interact with antigen-presenting cells, leading to activation and differentiation into effector T cells that can mount a specific immune response.

The process of helper T cell extravasation is precisely controlled, ensuring that these cells are only recruited to sites of inflammation or infection. This control is essential to prevent unwanted tissue damage and maintain immune homeostasis.'
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Proteins (1)

Compounds (4)