Allergic rhinitis is a common immediate hypersensitivity reaction. It affects mainly mucous membranes lining the nose. Typical symptoms include runny nose and nasal congestion. Pollens are the most common cause of allergic rhinitis. Tiny pollens of wind-pollinated plants like ragweed (Figure below) are the usual culprits. Other causes of allergic rhinitis include mold, animal dander, and dust. Allergic rhinitis may occur seasonally or year-round, depending on its cause.
Figure 24.11
Ragweed, a common cause of allergic rhinitis.
Allergic rhinitis is often called hay fever, although pollen—not hay—is the most likely cause. It is called hay fever because it is most common during the time of year when hay is cut. This is also the time of year when plant pollens are most concentrated in outdoor air.
Delayed Hypersensitivity Reaction
When an antigen causes allergy symptoms hours or days after exposure, the response is called a delayed hypersensitivity reaction. This is a cell-mediated immune response. Examples of allergens that cause delayed hypersensitivity reactions include poison ivy, poison oak, and poison sumac. If you have skin contact with these plants and are allergic to them, a rash, like the one in Figure below, may develop.
Figure 24.12
Allergic rash caused by contact with poison ivy.
Autoimmune Diseases
Autoimmune diseases occur when the immune system fails to recognize the body’s own molecules as self and attacks the body’s cells as though they were foreign invaders. Relatively common autoimmune diseases include rheumatoid arthritis, type 1 diabetes mellitus, multiple sclerosis, and systemic lupus erythematosus (Table below). These four diseases are described in the table below. They are currently incurable, but treatment can help relieve the symptoms and prevent some of the long-term damage.
Common Autoimmune Diseases Autoimmune Disease Object of Immune Attack Results of Immune Attack Treatment(s)
Rheumatoid arthritis Tissues inside joints Inflammation of joints, causing joint pain and damage and possible loss of mobility Anti-inflammatory drugs; drugs that suppress the immune system
Type 1 diabetes Insulin-producing cells of the pancreas Loss of ability to produce insulin, causing too much sugar in the blood and tissue and organ damage Insulin injections
Multiple sclerosis Myelin in the brain and spinal cord Loss of nerve function, causing muscle weakness, fatigue, visual problems, pain, and other symptoms Corticosteroid drugs; hormones that control the immune system
Systemic lupus erythematosus Joints, heart, lungs, or other organs Inflammation of joints or organs, causing serious joint or organ damage and pain Corticosteroid drugs; drugs that suppress the immune system
The causes of autoimmune diseases are not known for certain. One way autoimmunity may develop is through “molecular mimicry.” This occurs when a person is infected with pathogens bearing antigens similar to the person’s own molecules. When the immune system mounts an attack against the pathogens, it also attacks body cells with the similar molecules. Some people inherit genes that increase their risk for an autoimmune disease. Female sex hormones may also increase the risk. This may explain why autoimmune diseases are more common in females than males and why they usually begin after puberty.
Immunodeficiency Diseases
Immunodeficiency occurs when one or more components of the immune system are not working normally. As a result, the ability of the immune system to respond to pathogens and other threats is decreased. A person with immunodeficiency may suffer from frequent, life-threatening infections. In other words, an individual with a compromised immune system (for example, a person with AIDS) may be unable to fight off and survive infections by microorganisms that are usually benign. Immunodeficiency can be present at birth or acquired after birth.
Congenital Immunodeficiency
Congenital immunodeficiency is present at birth and usually caused by a genetic disorder. Such disorders are relatively rare. For example, thymic aplasia—a genetic disorder characterized by an absent or abnormal thymus—occurs in about 1 out of 4,000 births. People with thymic aplasia are unable to produce normal T cells. They have frequent infections and increased risk of autoimmune diseases.
Acquired Immunodeficiency
Acquired immunodeficiency occurs when immune function declines in a person who was born with a normal immune system. There are many possible causes for declining immune function. Age is one cause. The immune system naturally becomes less effective as we get older, starting in middle adulthood. This helps explain why older people are more susceptible to disease. Other possible causes of declining immune function include obesity, alcoholism, and illegal drug abuse. In developing countries, malnutrition is a common cause.
Many medications can interfere with normal immune function and cause immunodeficiency. Immune suppressive drugs are deliberately given to people with autoimmune diseases and transplanted organs. Many other drugs have immune suppression as a side effect. Chemotherapy drugs for cancer are especially likely to suppress the immune system.
Several kinds of cancer attack cells of the immune system and cause immunodeficiency. For example, in chronic lymphatic leukemia, abnormal B cells that can’t fight infection grow out of control and crowd out healthy B cells. Certain pathogens can also attack cells of the immune system. In fact, the virus known as HIV is the most common cause of immunodeficiency in the world today.
HIV and AIDS
HIV, or human immunodeficiency virus, is the virus that causes AIDS. AIDS stands for acquired immune deficiency syndrome. It is a late stage in the progression of an HIV infection.
HIV Transmission
HIV is transmitted, or spread, through direct contact of mucous membranes or the bloodstream with a body fluid containing HIV. Body fluids that can contain HIV include blood, semen, vaginal fluid, preseminal fluid, and breast milk. Transmission of the virus can occur through sexual contact or use of contaminated hypodermic needles. HIV can also be transmitted through a mother’s blood to her baby during late pregnancy or birth or through breast milk after birth. In the past, HIV was transmitted through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.
HIV and the Immune System
HIV destroys helper T cells. Recall that helper T cells are needed for normal humoral and cell-mediated immunity. When HIV enters a person’s bloodstream, proteins on the coat of the virus allow it to fuse with the host’s helper T cells. The virus injects its own DNA into the host’s helper T cells and uses the T cells’ “machinery” to make copies of itself. The copies of the virus bud off from the host’s cells, destroying the cells in the process. Copies of the virus go on to infect other helper T cells throughout the body.
During the first several weeks after HIV infection, the immune system tries to fight off the virus. As shown in Figure below, the initial immune response temporarily reduces the number of virus copies in the blood. However, the immune system is unable to destroy the virus, and it continues to multiply in the lymphatic system. How is HIV able to evade the immune system? There are at least two ways:
The virus undergoes frequent mutations that keep changing the antigens on its coat. This prevents antigen-specific lymphocytes from developing that could destroy the virus.
The virus uses the host’s cell membranes to form is own coat. This covers up viral antigens so they cannot be detected by the host’s immune system.
Figure 24.13
Average numbers of helper T cells and HIV copies in untreated HIV infections.
Over the next several years, helper T cells continuously decline in the blood, while copies of the virus keep increasing. As the number of helper T cells declines, so does the ability of the immune system to make an immune response. The HIV-infected person starts showing symptoms of a failing immune system, such as frequent infections.
Treatment with antiviral medications can slow down the increase in virus copies, although they do not eliminate the virus altog
ether. The medications usually lengthen the time between infection with HIV and the development of symptoms. However, currently there is no cure for HIV infection or AIDS and no vaccine to prevent infection, although this is a field of intense study by biomedical scientists.
AIDS
AIDS is not a single disease but a collection of symptoms and diseases. It is the result of years of damage to the immune system by HIV. AIDS is diagnosed when helper T cells fall to a very low level and the infected person develops one or more opportunistic diseases.
Opportunistic diseases are infections and tumors that are rare in people with a healthy immune system but common in immunodeficient people. Opportunistic diseases include pneumocystis pneumonia and Kaposi’s sarcoma, a type of cancer. The diseases are called opportunistic because they take advantage of the “opportunity” to infect a person with a damaged immune system that can’t fight back. Opportunistic diseases are often the direct cause of death of people with AIDS.
AIDS was first identified in 1981. Since then it has killed more than 25 million people worldwide, many of them children. The hardest hit region is sub-Saharan Africa, where antiviral medications are least available. The worldwide economic toll of AIDS is also enormous.
Lesson Summary
Allergies occur when the immune system makes an inflammatory response to a harmless antigen, called an allergen.
Autoimmune diseases occur when the immune system fails to distinguish self from nonself and attacks the body’s own cells.
In an immunodeficiency disease, the immune system does not work normally and cannot defend the body.
HIV is a virus that attacks cells of the immune system and eventually causes AIDS. It is the chief cause of immunodeficiency in the world today.
Review Questions
Describe anaphylaxis.
What is an autoimmune disease?
List three possible causes of acquired immunodeficiency.
Name two ways HIV can be transmitted.
Assume that you touch poison sumac and still have not developed a rash 12 hours later. Can you safely assume you are not allergic to the plant? Why or why not?
Rheumatic fever is caused by a virus that has antigens similar to molecules in human heart tissues. When the immune system attacks the virus, it also attacks the heart. What type of immune system disease is rheumatic fever? Explain your answer.
Draw a timeline to show the progression of an untreated HIV infection. Show how the numbers of HIV copies and helper T cells change through time.
Why are opportunistic infections a sign of immunodeficiency?
Further Reading / Supplemental Links
Bellenir, Karen, Ed., Allergy Information for Teens: Health Tips About Allergic Reactions Such As Anaphylaxis, Respiratory Problems, And Rashes. Omnigraphics, 2006.
Johanson, Paula, HIV and AIDS (Coping in a Changing World). Rosen Publishing Group, 2007.
http://en.wikibooks.org/wiki/Human_Physiology/The_Immune_System
http://www.cancer.gov/cancertopics/understandingcancer/immunesystem
http://www.kidshealth.org/teen/infections/stds/std_hiv.html
http://www.mayoclinic.com/health/allergy/AA99999
http://www.niaid.nih.gov/publications/immune/the_immune_system.pdf
http://www.nichd.nih.gov/health/topics/Primary_Immunodeficiency.cfm
http://www.4women.gov/FAQ/autoimmune.htm
http://en.wikipedia.org
Vocabulary
acquired immunodeficiency
Immunodeficiency that occurs when immune function declines in a person who was born with a normal immune system.
AIDS
Acquired immune deficiency syndrome; a late stage in the progression of an HIV infection.
allergen
Any antigen that causes an allergic reaction.
allergic rhinitis
A common immediate hypersensitivity reaction; affects mainly mucous membranes lining the nose; often called hay fever.
allergy
A disease in which the immune system makes an inflammatory response to a harmless antigen.
anaphylaxis
An allergic response in which there is a sudden, massive release of histamines throughout the body. This causes collapse of the circulatory system and severe constriction of the breathing passages. Without emergency treatment, anaphylaxis is likely to be fatal.
antihistamines
Drugs that reduce or eliminate the effects of histamines.
autoimmune diseases
Diseases that occur when the immune system fails to recognize the body’s own molecules as self and attacks the body’s cells as though they were foreign invaders.
delayed hypersensitivity reaction
When an antigen causes allergy symptoms hours or days after exposure.
epinephrine
The “fight-or-flight” hormone that your adrenal glands normally produce when you are in danger; suppresses non-emergency body processes, including the immune response.
HIV
The human immunodeficiency virus, the virus that causes AIDS.
immediate hypersensitivity reaction
When exposure to an antigen causes immediate allergy symptoms.
immunodeficiency
Occurs when one or more components of the immune system are not working normally; as a result, the ability of the immune system to respond to pathogens and other threats is decreased.
molecular mimicry
Occurs when a person is infected with pathogens bearing antigens similar to the person’s own molecules; when the immune system mounts an attack against the pathogens, it also attacks body cells with the similar.
opportunistic diseases
Infections and tumors that are rare in people with a healthy immune system but common in immunodeficient people; includes pneumocystis pneumonia and Kaposi’s sarcoma, a type of cancer.
Points to Consider
You read in this lesson that some types of cancer attack cells of the immune system and cause immunodeficiency. Cancer has previously been described as resulting from a loss of regulation of the cell cycle.
Why do you think immunodeficiency may lead to some cancers?
Can you think of a relationship between pathogens, the immune system, and the development of cancer?
Lesson 24.4: Environmental Problems and Human Health
Lesson Objectives
Explain how carcinogens cause cancer and list ways that cancer can be treated or prevented.
Identify causes of air pollution and describe how air pollution affects human health.
Define bioterrorism and explain how bioterrorism threatens human health.
Introduction
Cancer is one of many human diseases that can be caused by environmental problems. For example, air pollution may increase the risk of lung cancer. It can also cause or worsen asthma, cardiovascular diseases, and other health problems. Bioterrorism is another potential threat to human health. It may lead to severe environmental problems that have the potential to poison large numbers of people or cause epidemics of deadly diseases.
Carcinogens and Cancer
A carcinogen is anything that can cause cancer. Cancer is a disease in which abnormal body cells divide of control. Most carcinogens cause cancer by inducing mutations.
Carcinogens
Carcinogens may be pathogens, chemical substances, or radiation. Carcinogens often occur in nature. For example, some viruses are important carcinogens, causing as many as 15 percent of all human cancers. Different viruses cause different cancers. The human papilloma virus (HPV) is the main cause of cancer of the cervix in females. The hepatitis B virus can cause liver cancer, and the Epstein-Barr virus can cause cancer of the lymph nodes.
Other natural carcinogens include ultraviolet (UV) radiation from the sun. UV radiation is the leading cause of skin cancer. Radon is a natural radioactive gas that seeps into buildings from the ground. Exposure to radon can cause lung cancer. Asbestos can also cause lung can
cer. Asbestos is a mineral previously used for insulation and many other purposes. Today, it is largely banned because of its link to cancer.
Humans are exposed to many artificial carcinogens in the environment, including those in tobacco smoke. In fact, tobacco smoke may be the key source of human carcinogen exposure. It contains dozens of carcinogens including nicotine and formaldehyde, which is used to preserve dead bodies. As you will read below, other pollutants in the air can cause cancer as well.
Other artificial carcinogens are or were found in foods. Some food additives, such as certain food dyes, have proven to be carcinogens. Cooking foods at very high temperatures also causes carcinogens to form. For example, a carcinogen called acrylamide forms when carbohydrates are cooked at very high temperatures. It is found in foods such as French fries and potato chips. Barbecued or broiled meats also contain several carcinogens.
How Cancer Occurs
Carcinogens generally cause cancer by inducing mutations in genes that control cell division or other aspects of the cell cycle. The mutations typically occur in two types of genes: tumor-suppressor genes and proto-oncogenes (see chapter titled Molecular Genetics). Briefly:
CK-12 Biology I - Honors Page 120