Rolling of leucocytes on endothelial cells is mediated by which of the following proteins?
**Core Concept**
The rolling of leucocytes on endothelial cells is an initial step in the inflammatory response, mediated by specific adhesion molecules that facilitate the interaction between leucocytes and the vascular endothelium.
**Why the Correct Answer is Right**
The correct protein responsible for the rolling of leucocytes on endothelial cells is Selectin. Selectins are a family of cell adhesion molecules that are expressed on the surface of leukocytes and endothelial cells. They play a crucial role in the initial tethering and rolling of leukocytes on the endothelial lining of blood vessels, facilitating their eventual migration to sites of inflammation or injury. Specifically, P-selectin is stored in the Weibel-Palade bodies of endothelial cells and is rapidly translocated to the cell surface upon activation, while L-selectin is constitutively expressed on the surface of leukocytes.
**Why Each Wrong Option is Incorrect**
* **Option A:** Integrins are a family of cell adhesion molecules that play a key role in the firm adhesion and transmigration of leukocytes across the endothelial barrier, but are not primarily involved in the rolling phase.
* **Option B:** Cadherins are a family of cell adhesion molecules that are primarily involved in the adhesion of cells to each other within tissues, rather than the interaction between leukocytes and endothelial cells.
* **Option C:** Immunoglobulin superfamily members, such as ICAM-1 and VCAM-1, are involved in the firm adhesion and transmigration of leukocytes across the endothelial barrier, but are not primarily involved in the rolling phase.
**Clinical Pearl / High-Yield Fact**
To remember the key adhesion molecules involved in leukocyte recruitment, the acronym "SILK" can be used: Selectins (L and P) for rolling, Integrins for firm adhesion, Leukocyte function-associated antigen-1 (LFA-1) for firm adhesion, and Kinesin for chemotaxis.
**Correct Answer:** C.