Читать книгу Immunology - Richard Coico - Страница 77

Although fever is one of the most common manifestations of infection and inflammation, there is still limited information about the significance of fever in the course of infection in mammals. In addition to the effects of acute phase proteins on the hypothalamus during inflammatory responses, fever is caused by many bacterial products, most notably the endotoxins (lipopolysaccharide [LPS]) of Gram‐negative bacteria. Exposure of innate immune cells (monocytes and macrophages) to LPS causes the release of cytokines called endogenous pyrogens. Examples of cytokines with endogenous pyrogenic properties include IL‐1 and certain interferons (see Chapter 11). Cells in other tissues can also produce these cytokines. For example, the keratinocytes present in skin contain IL‐1. Interestingly, when the skin is overexposed to the ultraviolet rays of the sun (sunburn), keratinocytes are physically damaged, causing them to release their contents, including IL‐1. Within a few hours, IL‐1 induces the hypothalamus to raise body temperature (fever)—a phenomenon many have experienced after a summer day at the beach, with accompanying chills and malaise. Fortunately, the ultraviolet rays can be blocked by a variety of topical products to prevent skin damage. Many tissues also synthesize substances that are harmful to microorganisms. Examples include degradative enzymes, toxic free radicals, and, as noted above, acute phase proteins

Figure 3.11. Adhesion molecules involved in leukocyte tethering, rolling, and adhesion to endothelium leading to transendothelial migration from blood to tissue