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Ebook Microbiology principles and explorations (8th edition): Part 2

(BQ) Part 2 book "Microbiology principles and explorations" presents the following contents: Innate host defenses, basic principles of adaptive immunity and immunization, immune disorders, urogenital and sexually transmitted diseases, diseases of the respiratory system, oral and gastrointestinal diseases, diseases of the nervous system, applied microbiology, | C H A P T E R 16 Innate Host Defenses Sometimes, when you can’t kill something that is harmful, the best thing to do is to wall it off. But if the wall gets too thick, too rigid, or just too many walls are needed, then your defense mechanism can wind up hurting you. In other words, things that your immune system does to try to protect you can sometimes be harmful. Granulomas are such an immune response. A granuloma is a thick layer of cells around irritants such as chemicals, microbes, parasites, or even tissue damaged by trauma. A granuloma forms when the irritant can’t be gotten rid of; e.g., Mycobacterium leprae bacteria which have been phagocytized by macrophages are difficult to kill because they divide so very slowly. A person with a strong immune response will form a granuloma around them typical of leprosy (now called Hansen’s disease). This is what forms the disfiguring lumps and bumps. These lack sensation due to nerve damage, allowing infections to go unnoticed. Patient suffering from advanced leprosy (Hansen’s disease). (Science Source/Photo Researchers) We can look at infectious disease as a battle between the power of infectious agents to invade and damage the body and the body’s powers to resist such invasions. In Chapters 14 and 15 we considered how infectious agents enter and damage the body and how they leave the body and spread through populations. In the next three chapters we consider how the body resists invasion by infectious agents. We begin this chapter by distinguishing between adaptive and innate defenses. Until recently these were called specific and nonspecific defenses. As the nonspecific defenses were studied, it became apparent that they involved very specific interactions but did not require a previous exposure to be active, hence the term innate defense. Then we will look at the innate defense mechanisms in more detail to see how they function in protecting the body against infectious agents. 462 INNATE AND ADAPTIVE HOST .