Cellular Adhesion Molecules

Often cells must interact dynamically and transiently, rather than form permanent attachments. Proteins called cellular adhesion molecules, or CAMs for short, guide cells on the move. Consider a white blood cell moving in the bloodstream to the site of an injury, where it is required to fight infection. Imagine that such a cell must reach a woody splinter embedded in a person's palm (fig. 3.9).

Once near the splinter, the white blood cell must slow down in the turbulence of the bloodstream. A type of CAM called a selectin does this by coating the white blood cell and providing traction. The white blood cell slows to a roll and binds to carbohydrates on the inner capillary surface. Clotting blood, bacteria, and decaying tissue at the injury site release biochemicals (chemoat-tractants) that attract the white blood cell. Finally, a type of CAM called an integrin contacts an adhesion receptor protein protruding into the capillary space near the splinter and pushes up through the capillary cell membrane, grabbing the passing slowed white blood cell and directing it between the tilelike cells of the capillary wall. White blood cells collecting at an injury site produce inflammation and, with the dying bacteria, form pus. (The role of white blood cells in body defense is discussed further in chapter 16, pp. 661-666.)

Extracellular side of membrane

Fibrous proteins

Figure 3.7

Fibrous proteins

Blood Vessels

Double layer of phospholipid molecules

Cytoplasmic side of membrane

Cholesterol molecules

Double layer of phospholipid molecules

Cytoplasmic side of membrane

Cholesterol molecules v Hydrophobic phospholipid "tail" Hydrophilic phospholipid "head"

The cell membrane is composed primarily of phospholipids (and some cholesterol), with proteins scattered throughout the lipid bilayer and associated with its surfaces.

Brooke Blanton was born lacking the CAMs that enable white blood cells to adhere to blood vessel walls. As a result, her sores do not heal, never forming pus because white blood cells never reach injury sites. Brooke's earliest symptoms were teething sores that did not heal. Today, Brooke must be very careful to avoid injury or infection because her white blood cells, although plentiful and healthy, zip past her wounds.

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Responses

  • MUNGO
    What cellular adhesion molecule coats white blood cells for traction?
    5 years ago

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