lymphocyte chemotaxis

Definition

Target type: biologicalprocess

The directed movement of a lymphocyte in response to an external stimulus. [GOC:hjd, GOC:jid, PMID:12391252]

Lymphocyte chemotaxis is a fundamental biological process that enables lymphocytes, a type of white blood cell crucial for adaptive immunity, to navigate towards specific locations within the body in response to chemical signals. This directed migration is essential for coordinating immune responses and effectively targeting sites of infection, inflammation, or tissue damage. Here's a detailed breakdown of the process:

**1. Chemokine Signaling:**

* Chemokines, small secreted proteins, act as chemical messengers that attract lymphocytes to specific locations. These chemokines are produced by various cells, including immune cells, endothelial cells, and fibroblasts, in response to inflammatory stimuli or tissue damage.
* Each chemokine exhibits specificity for certain types of lymphocytes, such as T cells, B cells, or NK cells, ensuring the recruitment of the appropriate immune cell population.
* Chemokines bind to specific receptors on the surface of lymphocytes, initiating a cascade of intracellular signaling events.

**2. Signal Transduction and Cellular Activation:**

* Upon chemokine binding, the chemokine receptors activate intracellular signaling pathways. This involves the activation of G proteins, which then stimulate phospholipase C (PLC) and the production of second messengers like inositol triphosphate (IP3) and diacylglycerol (DAG).
* IP3 triggers the release of calcium ions (Ca2+) from intracellular stores, leading to a rise in intracellular Ca2+ levels. This Ca2+ influx is essential for initiating the chemotaxis cascade.
* DAG activates protein kinase C (PKC), which phosphorylates various proteins involved in cytoskeletal reorganization and cell migration.

**3. Cytoskeletal Rearrangement and Polarization:**

* The increased intracellular Ca2+ concentration and PKC activation lead to the reorganization of the lymphocyte's cytoskeleton, primarily involving actin filaments.
* This cytoskeletal rearrangement results in the formation of a polarized structure, with a leading edge (lamellipodium) extending towards the chemokine source and a trailing edge (uropod) at the rear of the cell.

**4. Directed Migration:**

* The lamellipodium extends through the polymerization of actin filaments, allowing the lymphocyte to adhere to and move across the extracellular matrix.
* The uropod acts as a point of attachment, providing traction for the cell's forward movement.
* Integrins, transmembrane receptors that bind to extracellular matrix components, play a crucial role in cell adhesion and migration during chemotaxis.

**5. Detachment and Reorientation:**

* As the lymphocyte moves forward, the uropod detaches from the extracellular matrix, allowing the cell to reorient itself towards the chemokine gradient.
* This process of attachment, detachment, and reorientation is repeated, allowing the lymphocyte to efficiently navigate towards the chemokine source.

**6. Chemokine Gradient Sensing and Chemotactic Index:**

* Lymphocytes can sense even small differences in chemokine concentration, enabling them to navigate along chemokine gradients.
* The chemotactic index, which is a measure of the cell's directed movement along a chemokine gradient, indicates the strength of the chemotactic response.

**7. Importance of Lymphocyte Chemotaxis:**

* **Immune Surveillance:** Chemotaxis enables lymphocytes to patrol tissues and monitor for signs of infection or inflammation.
* **Immune Response Coordination:** The directed migration of lymphocytes ensures that the appropriate immune cells are recruited to specific sites of infection or inflammation.
* **Adaptive Immunity:** Chemotaxis allows T cells and B cells to migrate to lymph nodes and other secondary lymphoid organs, where they encounter antigens and initiate adaptive immune responses.
* **Wound Healing:** Chemotaxis is involved in the recruitment of immune cells to sites of tissue injury, facilitating the healing process.

**Disruption of lymphocyte chemotaxis can lead to impaired immune responses, making individuals more susceptible to infections and other diseases.**'"

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