Migration of Specific Leukocyte Subsets in Response to Cytokine or Chemokine Application In Vivo

The host inflammatory response is a complex process characterized by several different steps (or phenomena) all contributing to the well-known macroscopic symptoms of this condition, which are pain, fever, redness, swelling, and, in the case of chronic inflammation (such as rheumatoid arthritis), loss of function (see Chapters 1 and 12 ). These symptoms are the consequence of a series of local (i.e., at the site of the inflammatory insult) and systemic changes. Locally, arterioles, capillaries, and venules dilate with consequent increase in permeability and blood flow; this leads to exudation of fluid and proteins (humoral response ); finally, leukocytes also migrate into the inflammatory site (cellular response ). The latter process is by far the most important because “...the accumulation and subsequent activation of leukocytes are central events in the pathogenesis of virtually all forms of inflammation.” (1 ). For this reason, the acquisition of information regarding the molecular mechanisms responsible for leukocyte accumulation during inflammation can, on one hand, increase our knowledge of the etiology of inflammatory pathologies and, on the other hand, lead to the discovery of novel targets for antiinflammatory therapy.