The Vasculitides

© Dirk Biddle

1.7.1.8 Macrophages

Macrophages are the body’s major phagocytic cells and recognize and remove unwanted particulate matter including invading bacteria, protozoa, fungi, helminths and also the products of inflammation, antigens and toxins, as well as providing defence against tumours, especially metastasising tumours. Macrophages are highly deformable cells and are able to penetrate into the smallest gaps in vascular walls and work their way into the most diverse of tissue types. They form semi-liquid cytoplasmic projections (filopodia) which are used for motility and for trapping pathogens and other foreign bodies. In chronic inflammation, macrophages act as scavengers. Macrophages in their activated state are able to produce more than one hundred different substances and by means of antibody-dependent cell-mediated cytotoxicity (ADCC) they are able to kill or damage extracellular targets. After phagocytosis macrophages can also prevent intracellular parasitic organisms from replication. In addition, macrophages also have an important role in the presentation of antigens (as antigen presenting cells - APCs) to T-cells and also in activating T-cells with interleukin-1 (IL-1)release. Macrophages can also become giant cells (see next section) in the formation of granulomas.

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Antigen: A (usually) protein or carbohydrate substance (as a toxin or enzyme) capable of stimulating an immune response. (M+)
Interleukin-1 (IL-1): A soluble protein (17 kD: 152 amino acids) secreted by monocytes, macrophages or accessory cells involved in the activation of both T-lymphocytes and B lymphocytes and potentiates their response to antigens or mitogens.
Its biological effects include the ability to replace macrophage requirements for T-cell activation, as well as affecting a wide range of other cell types. At least two IL-1 genes are active and alpha and beta forms of IL-1 are recognised.
It is released early in an immune system response by monocytes and macrophages. It stimulates T-cell proliferation and protein synthesis. Another effect of IL-1 is that it causes fever. (OMD).
Granuloma: Chronic inflammatory lesion characterised by large numbers of cells of various types (macrophages, lymphocytes, fibroblasts, giant cells), some degrading and some repairing the tissues. (OMD)