Porth's Essentials of Pathophysiology, 4e

55

Inflammation, the Inflammatory Response, and Fever

C h a p t e r 3

Blood flow

2

Cellular Phase: Leukocyte Margination, Adhesion, and Transmigration. The cellular phase of acute inflammation involves the delivery of leukocytes, mainly neutrophils, to the site of injury so they can perform their nor- mal functions of host defense. The delivery and activation of leuko- cytes can be divided into the follow- ing steps: adhesion and margination, transmigration, and chemotaxis. The recruitment of leukocytes to the precapillary venules, where they exit the circulation, is facilitated by the slowing of blood flow and margin- ation along the vessel surface. Leukocyte adhesion and transmi- gration from the vascular space into the extravascular tissue is facilitated by complementary adhesion mole- cules (e.g., selectins, integrins) on the leukocyte and endothelial sur- faces. After extravasation, leuko- cytes migrate in the tissues toward the site of injury by chemotaxis, or locomotion oriented along a chemi- cal gradient. Leukocyte Activation and Phagocytosis. Once at the sight of injury, the products generated by tissue injury trigger a number of leu- kocyte responses, including phago- cytosis and cell killing. Opsonization of microbes (1) by complement fac- tor C3b and antibody facilitates rec- ognition by neutrophil C3b and the antibody Fc receptor. Receptor acti- vation (2) triggers intracellular sig- naling and actin assembly in the neutrophil, leading to formation of pseudopods that enclose the microbe within a phagosome. The phago- some (3) then fuses with an intracel- lular lysosome to form a phagolysosome into which lyso- somal enzymes and oxygen radicals (4) are released to kill and degrade the microbe.

Endothelial cells

Firm adhesion Transmigration

Rolling

Capillary

Neutrophil

Neutrophil

2

Transmigration

1

Margination

Bacteria

3

Chemotaxis

3

1

2

Phagosome

Fc receptor

Fc

C3b

C3b receptor

3

4

Phagolysosome