35.4 Immune System Disorders Lesson Overview 35.4 Immune System Disorders

THINK ABOUT IT A healthy immune system accurately distinguishes “self” from “other” and responds appropriately to dangerous invaders in the body. Sometimes, however, the immune system attacks the wrong targets. Other times, the immune system itself is disabled by disease. What happens in these cases?

When the Immune System “Misfires” How can misguided immune responses cause problems?

When the Immune System “Misfires” How can misguided immune responses cause problems? A strong immune response to harmless antigens can produce allergies, asthma, and autoimmune disease. When the immune system attacks the body’s own cells, it produces an autoimmune disease.

When the Immune System “Misfires” The immune systems of some people overreact to harmless antigens, such as pollen, dust mites, mold, and pet dander. A strong immune response to harmless antigens can produce allergies, asthma, and autoimmune disease. .

Allergies Antigens that cause allergic reactions are called allergens. Pet dander, dead skin shed from cats and dogs, is a common allergen.

Allergies When allergens enter the body of people affected by allergies, they trigger an inflammatory response by causing mast cells to release histamines. If this response occurs in the respiratory system, it increases mucus production and causes sneezing, watery eyes, a runny nose, and other irritations. Drugs called antihistamines help relieve allergy symptoms by counteracting the effects of histamines.

Asthma Allergic reactions in the respiratory system can create a dangerous condition called asthma. Asthma is a chronic disease in which air passages narrow, causing wheezing, coughing, and difficulty breathing. Both hereditary and environmental factors influence asthma symptoms. Asthma attacks can be triggered by respiratory infections, exercise, emotional stress, and certain medications. Other triggers include cold or dry air, pollen, dust, tobacco smoke, pollution, molds, and pet dander.

Asthma Severe asthma can lead to permanent damage or destruction of lung tissue if treatment is not started early enough or if medications are not taken properly. There is no cure, but people with asthma can sometimes control the condition. If the attacks are caused by an allergen, tests can identify which allergens cause the problem. Inhaled medications can relax smooth muscles around the airways and relieve asthma symptoms.

Autoimmune Diseases Sometimes a disease occurs in which the immune system fails to properly recognize “self,” and it attacks cells or compounds in the body as though they were pathogens. When the immune system attacks the body’s own cells, it produces an autoimmune disease. Examples of autoimmune diseases are Type I diabetes, rheumatoid arthritis, and lupus.

Autoimmune Diseases In Type I diabetes, antibodies attack insulin-producing cells in the pancreas. In rheumatoid arthritis, antibodies attack connective tissues around the joints. Lupus is an autoimmune disease in which antibodies attack organs and tissues leading to areas of chronic inflammation throughout the body.

Autoimmune Diseases Some autoimmune diseases can be treated with medications that alleviate specific symptoms. For example, people with Type I diabetes can take insulin. Other autoimmune diseases are treated with medications that suppress the immune response. However, these medications also decrease the normal immune response and must be monitored.

HIV and AIDS What causes AIDS and how is it spread?

HIV and AIDS What causes AIDS and how is it spread? In 1983, researchers identified the cause of AIDS—a virus they called human immunodeficiency virus (HIV). The only no-risk behavior with respect to HIV transmission is abstinence from sexual activity and intravenous drug use.

HIV and AIDS During the late 1970s, physicians began reporting serious infections produced by microorganisms that didn’t normally cause disease. Previously healthy people began to suffer from Pneumocystis carinii pneumonia, Kaposi sarcoma (a rare form of skin cancer), and fungal infections of the mouth and throat. Since these diseases are normally prevented by a healthy immune response, doctors concluded that these patients must have weakened immune systems. Diseases that attack a person with a weakened immune system are called opportunistic diseases.

HIV and AIDS Doctors ultimately recognized that these illnesses were symptoms of a new disorder they called acquired immunodeficiency syndrome (AIDS). In 1983, researchers identified the cause of AIDS—a virus they called human immunodeficiency virus (HIV).

HIV HIV is deadly for two reasons. First, HIV can hide from the defenses of the immune system. Second, HIV attacks key cells within the immune system, leaving the body with inadequate protection against other pathogens.

HIV HIV is a retrovirus that carries its genetic information in RNA, rather than DNA. When HIV attacks a cell, it binds to receptor molecules on the cell membrane and inserts its contents into the cell.

Target: T Cells HIV travels through the blood, where it binds to helper T cells—the command centers of the specific immune response. Once inside the cell, the virus directs the cell to produce many new viruses. These new viruses are quickly released back into the blood, where they infect new cells.

Target: T Cells Over time, HIV destroys more and more T cells, crippling the ability of the immune system to fight HIV and other pathogens. The progression of HIV infection can be monitored by counting helper T cells. The fewer helper T cells, the more advanced the disease, and the more susceptible the body becomes to other diseases. When an HIV-infected person’s T cell count reaches about one sixth the normal level, he or she is diagnosed with AIDS.

HIV Transmission Although HIV is deadly, it is not easily transmitted. It is not transmitted through coughing, sneezing, sharing clothes, or other forms of casual contact. HIV can only be transmitted through contact with infected blood, semen, vaginal secretions, or breast milk. The four main ways that HIV is transmitted is through sexual intercourse with an infected person, sharing needles with an infected person, contact with infected blood or blood products, or from an infected mother to her child during pregnancy, birth, or breast-feeding.

Preventing HIV Infection You can choose behaviors that reduce your risk of becoming infected with HIV. Within a committed relationship, such as marriage, sexual fidelity between two uninfected partners presents the least risk of becoming infected with HIV. People who share contaminated needles to inject themselves with drugs are at an increased risk for contracting HIV. People who have sex with drug abusers are also at an increased risk. Before 1985, HIV was transmitted to some patients through transfusions of infected blood or blood products. But, such cases have been virtually eliminated by screening the blood supply for HIV antibodies and by discouraging potentially infected individuals from donating blood.

Preventing HIV Infection This graph shows the increase in cases 13-24-year-olds living with AIDS in the United States.

Can AIDS Be Cured? At present, there is no cure for AIDS. New drugs, however, make it possible to survive HIV infection for years. Unfortunately, HIV mutates and evolves rapidly. The virus has evolved into many strains that are resistant to most drugs used against them. No one has developed a vaccine that offers protection for any length of time.

Can AIDS Be Cured? At present, the only way to control the virus is to use a combination of expensive drugs that fight the virus in several ways. Current drugs interfere with the enzymes HIV uses to insert its RNA into a host cell, to convert RNA to DNA, and to integrate its DNA into the host’s DNA. The knowledge that HIV can be treated has given some people the idea that HIV infection is not serious. However, that idea is dead wrong, because there is no cure for HIV.