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Microbiology, 2021

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CHAPTER 19<br />

Diseases of the Immune System<br />

Figure 19.1 Bee stings and other allergens can cause life-threatening, systemic allergic reactions. Sensitive<br />

individuals may need to carry an epinephrine auto-injector (e.g., EpiPen) in case of a sting. A bee-sting allergy is an<br />

example of an immune response that is harmful to the host rather than protective; epinephrine counteracts the<br />

severe drop in blood pressure that can result from the immune response. (credit right: modification of work by Carol<br />

Bleistine)<br />

Chapter Outline<br />

19.1 Hypersensitivities<br />

19.2 Autoimmune Disorders<br />

19.3 Organ Transplantation and Rejection<br />

19.4 Immunodeficiency<br />

19.5 Cancer Immunobiology and Immunotherapy<br />

INTRODUCTION An allergic reaction is an immune response to a type of antigen called an allergen. Allergens<br />

can be found in many different items, from peanuts and insect stings to latex and some drugs. Unlike other<br />

kinds of antigens, allergens are not necessarily associated with pathogenic microbes, and many allergens<br />

provoke no immune response at all in most people.<br />

Allergic responses vary in severity. Some are mild and localized, like hay fever or hives, but others can result in<br />

systemic, life-threatening reactions. Anaphylaxis, for example, is a rapidly developing allergic reaction that<br />

can cause a dangerous drop in blood pressure and severe swelling of the throat that may close off the airway.<br />

Allergies are just one example of how the immune system—the system normally responsible for preventing

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