The neutrophils constitute the largest population of white blood cells and the first line of defense of mammalian organisms against invading microbes. They circulate passively in the blood and are rapidly recruited into inflamed tissues, where they help eliminate pathogens and other inflammatory agents. Like other leukocytes, neutrophils are alarmed by chemotactic molecules that arise within the tissues and direct their migration through the wall of the local capillary vessels and their accumulation into the lesion. The neutrophil responses to chemoattractants involve active motion and a series of release reactions. These functions and their mechanisms are usually studied in suspensions of purified neutrophils, which are stimulated with chemotactic receptor agonists.

The shape change reflects the activation of the motile apparatus. As shown by scanning electron microscopy, chemotactically stimulated neutrophils rapidly form large, thin cytoplasmic lamellae that are believed to be important for adhesion and migration. In stirred suspensions this response can be assessed by laser nephelometry as a transient increase in light transmission that reaches a maximum in IO-15 s and returns to control levels in 2-4 min (94, 410, 411).