Neutrophils, or neutrophil polymorphonuclear leucocytes,
respond to chemotactic signals and leave capillaries by a complex process, involving margination (flowing nearer to the endothelial lining of blood vessels), rolling and then attaching (margination), following which they emigrate between the endothelial cells (extravasation, or diapedesis). Several mediators are involved. They include substances produced by micro-organisms, and by the cells participating in the inflammatory process. One such is a substance called interleukin-1 (IL-1), which is released by macrophages as a result of infection or tissue injury. Another is histamine, released by circulating basophils, tissue mast cells, and blood platelets. It causes capillary and venular dilatation. C3a and C5a produced during complement activation, are chemotactic for phagocytic cells. Another group of substances produced are the acute phase proteins. As a consequence of tissue damage, the liver produces a substance called C-reactive protein (CRP), which is so called on account of its ability to attach to the C-polysaccharide component of the cell wall of bacteria and fungi. This activates the complement system by the classical pathway, and as a result C3a is formed and coats the organism, facilitating its phagocytosis.
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Neutrophil polymorph. 