Pavementing vs. Margination — What's the Difference?

Pavementing refers to the process where leukocytes (white blood cells) adhere to the endothelial cells lining the blood vessel walls. This phenomenon is crucial in the body's inflammatory response, allowing leukocytes to position themselves for potential migration through the vessel wall to reach affected tissues. Margination, on the other hand, describes the movement and accumulation of leukocytes to the periphery of blood flow within vessels, a preliminary step before pavementing occurs.

During an inflammatory response, blood flow dynamics change, causing leukocytes to move to the sides of blood vessels in a process known as margination. This is facilitated by the reduced flow rate and increased viscosity of blood near the vessel walls. Following margination, leukocytes undergo pavementing, where they form strong adhesions with endothelial cells, a critical step before they can exit the bloodstream to attend to sites of infection or injury.

The adhesion molecules involved in pavementing, such as selectins and integrins, play a key role in the firm attachment of leukocytes to the endothelium. Margination, however, is more influenced by hemodynamic factors and the interaction of leukocytes with plasma proteins, which help in positioning the leukocytes closer to the vessel walls.

In terms of their role in the immune response, pavementing is directly involved in the process of leukocyte extravasation, where leukocytes exit the bloodstream. Margination, while not directly involved in extravasation, is essential for positioning leukocytes in a way that they can engage in pavementing and subsequent transmigration.

Pavementing and margination, though distinct processes, are interconnected stages of the leukocyte adhesion cascade, a series of events that enable leukocytes to reach sites of tissue damage or infection efficiently. The effective coordination of these processes is vital for a robust and timely immune response.