Adhesion: chemokines released by macrophages activate the rolling leukocytes. This causes the immobilisation of the leukocytes, despite the shear forces of the ongoing blood flow Diapedesis: the passage of blood cells through intact vessel walls of the capillaries
All leukocytes follow these five basic steps, but each type of leukocyte has its own characteristics.
are the first type of leukocyte to respond to cell injury. Once at the site of injury, neutrophils remove antigens and necrotic tissue through phagocytosis. Once a neutrophil has performed phagocytosis it dies, releasing digested molecules, and digestive enzymes. The digestive enzymes cause injury to surrounding cells. This by-product is called “bystander injury”. The mixture of dead tissue, dead leukocytes and dead antigen is called purulent exudate or . As neutrophils are used up, the bone marrow releases new, immature neutrophils into the blood. An increase in circulating, immature neutrophils is called “ ”.
are the second type of leukocytes to enter the site of injury. Once a
monocyte migrates out of the blood flow into the tissue it is called a . Macrophages patrol the tissue to destroy pathogens and necrotic tissue through the process of phagocytosis. Macrophages have a much longer lifespan than neutrophils. In tissue, macrophages can live for several weeks, and can consume multiple cells and pathogens. In some cases, several macrophages will join together to form a phagocytic “super-complex” called a multinucleated giant cell. are the leukocytes responsible for specific immune defence. Lymphocytes produce antibodies (Ab) against specific antigens (Ag) once the antigen has been digested and processed by another leukocyte. Lymphocytes can become cells. Memory cells remain in the lymph nodes and can produce a rapid, specific immune response if the body is exposed to an antigen more than once. are leukocytes associated with allergic reactions. Eosinophils are capable of phagocytosis, but like neutrophils, cause bystander injury to normal tissue near to a pathogen. Usually a large protein molecule triggers an allergic reaction. These proteins are not invasive or harmful like other antigens, but they trigger an immune response because the body recognizes the molecule as other than self. are associated with most types of immune responses. They have a slight phagocytic function but are more important for the fact that they produce and release at the site of injury.
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