The Nonspecific Immune Response

<h1>Text Preview</h1> <p>Pathogens that manage to penetrate the body's external barriers encounter the internal environment of the body. Let's think about that splinter. It penetrated the skin, allowing the bacteria on the wood to enter the body. The body now needs to destroy the bacteria before they cause an infection to develop. That’s where the second line of defense comes in: a nonspecific immune response. An immune response is the body's reaction to invasion by a pathogen. </p> <p>Our body's nonspecific immune response depends largely on phagocytosis, the ingestion of pathogens by certain types of white blood cells. In phagocytosis, the pathogen enters the white blood cell via endocytosis. The white blood cells involved in phagocytosis are collectively known as phagocytes.</p> <p>The majority of phagocytes are neutrophils. These white blood cells leave the blood at sites of infection and ingest and destroy pathogens. Neutrophils generally self-destruct in the process. Like neutrophils, monocytes are phagocytes that leave the blood. But when they enter a tissue, they develop into macrophages, or "big eaters." After ingesting the pathogens, macrophages destroy the invaders with digestive enzymes. Macrophages also ingest dead cells. Macrophages live much longer than newtrophils and are found in large numbers in the lymphatic organs, including the lymph nodes.</p> <p>Phagocytes generally ingest foreign material and dead cells.</p> <p>Cells that have been infected by viruses are destroyed by a different type of white blood cell called a natural killer cell. Natural killer cells can also identify cancer cells and destroy them. Instead of ingesting infected or cancerous cells, natural killer cells attack the plasma membrane, causing the cells to rupture. </p> <p>In addition to white blood cells, various proteins are involved in the body’s nonspecific immune defenses. We mentioned one such protein, the enzyme lysozyme, in the context of saliva and tears.</p> <p>There are also about 20 different types of proteins that work with immune system cells as part of the immune response. These proteins are known as the complement system because they complement the work of the white blood cells. For example, some complement proteins attract white blood cells to the site of infection.</p> <p>Another group of proteins, called interferons, are produced by virus-infected cells to help other cells avoid infection. Now that researchers understand the role of interferons, they can use these proteins to develop medical treatments. Interferon treatments are most effective in treating short-term viral infections like colds and the flu. But they're also used to treat long-term infections including acute cases of hepatitis. </p> <p>When you get a splinter, you might notice that the area around the splinter becomes swollen and red. It may even become warm to the touch. These changes are all part of the inflammatory response, or inflammation. Inflammation is a local response to an injury or infection. </p> <p>At the site of an injury, certain white blood cells release a chemical called histamine. The presence of histamine causes small blood vessels in the area to dilate, increasing the flow of blood to the region. The area gets red and swollen—a signal that the inflammatory response has been triggered.</p> <p>Histamine also makes the small blood vessels and capillaries more permeable, allowing the passage of more white blood cells into the damaged tissue. The white blood cells then start fighting the pathogens and healing the injury — this is the immune response at work.</p> <p>An allergic reaction may be triggered by an overactive immune response, such as the inappropriate release of histamine. That's why many allergy medicines contain antihistamines, to interfere with the action of histamine in the body.</p> <p>In addition to local inflammation, there may also be a systemic response, involving the whole body. For example, chemical signals from the inflammatory response can increase the production of white blood cells to help fight an infection. This is the body's way of calling in extra reinforcements.</p> <p>Another systemic response is a fever. Some fevers are caused by toxins released by pathogenic microbes. But the body can also cause fever in order to help protect itself. During an infection, certain cells release molecules that cause the body’s thermostat to be set at a higher temperature. The increased temperature inhibits the growth of many pathogens. It also increases the rate of repair by speeding up the reactions involved in healing.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>