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Eosinophil.
These cells have the purpose of giving large parasites such as helminths, a hard time. They attach via C3b receptors, the C3b having been produced during the course of alternative pathway complement activation by the helminth. The eosinophils release various substances from their eosinophilic granules. These include major basic protein (MBP), plus cationic proteins, peroxidase, arylsulphatase B, phospholipase D and histaminase. The granule contents are capable of damaging the parasite membrane.
Neutrophil polymorph.
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
Monocyte.
Monocytes circulate in the peripheral blood prior to emigration into the tissues. Within certain organs they have special names, e.g. in liver they are known as Kupfer cells, in brain as microglia, in kidney as mesangial cells, and in bone as osteoclasts. Elsewhere they are referred to as tissue macrophages.
Phagocytosis is mediated by macrophages a
Basophil.
Basophils are non-phagocytic cells which, when activated, release numerous compounds from the basophilic granules within their cytoplasm. They play a major role in allergic responses, particularly type I hypersensitive reactions.
Erythrocyte (red blood cell).
Lymphocyte.
Lymphocytes are produced within bone marrow (a primary lymphoid organ).
If they achieve immune-competence within the bone marrow, they are known as B cells, or if in the thymus (also a primary lymphoid organ), they are known as T cells. Organized lymphoid tissue elsewhere is known as secondary lymphoid tissue, and includes lymph nodes, adenoids, tonsils and mucosa associated tissue (MALT). MALT includes bronchus associated lymphoid tissue (BALT), gut associated lymphoid tissue (GALT), naso-phayngeal associated lymphoid tissue (NALT), and uro-genital associated lymphoid tissue. These lymphoid organs receive antigens from the tissues and mucosal surfaces. Antigens that succeed in invading the blood stream are intercepted in the spleen.
Lymphocytes respond to presented antigens by the production of antibodies (by B cells), to be described later, or lymphokines (by T and B cells). These have many actions, including control of the adaptive immune response by secondary action on the participating cells, and, in the case of cytolytic T cells, in killing virally-infected host cells.
Lymphocytes possess receptors for these polypeptide antigens. The ability of a molecule or molecular configuration to induce an immune response is spoken of as immunogenicity, and the molecule as an immunogen. A molecule able to react with the ensuing antibody or T cell receptor is spoken of as an antigen. Some antigens, whilst able to react, are unable to induce, i.e. they lack immunogenicity and are known as haptens.
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