Immune Response Is Damaged By Infection Biology Essay

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AIDS (acquired immune deficiency syndrome) is a disease in which the immune response is damaged by infection with the human immunodeficiency virus (HIV). The virus infects a type of white blood cell called a T4-lymphocyte (or helper cell), which is crucial for the regulation of immune mechanisms. As a result, the body becomes highly susceptible to a range of opportunistic infections and cancers. Despite vast research efforts, no cure has yet been found.

AIDS does not develop immediately after infection with HIV. At first, the infected person may have no obvious symptoms and may be unaware that he or she is carrying the virus. Others may suffer minor symptoms, such as weight loss, fever, skin inflammation, and diarrhea. During this period, the body's immune system is thought to be waging a war against the virus. Eventually, the immune system is overcome, and full-blown AIDS develops.

The interval between infection and onset of AIDS is highly variable. Around half of those infected with HIV develop AIDS within eight to nine years after infection. The proportion who remain well indefinitely is not yet known.

History

In 1981, the Center for Disease Control (CDC) in Atlanta, Georgia, was alerted to reports of cases of a rare lung infection in previously healthy homosexual men in Los Angeles, and then in New York. Infection was found to be with Pneumocystis carinii, a protozoan organism that had previously caused pneumonia only in patients whose immune defenses were suppressed.

Later, cases of a rare tumor (Kaposi's sarcoma) were reported in young homosexual men; it was recognized as a slow-growing skin cancer previously seen mainly in Africa. In people with AIDS, the tumor behaved much more aggressively, and was found in parts of the body other than the skin.

Soon it appeared that there was a rapidly increasing epidemic of conditions associated with depression of the immune system. Several other infections were reported, most of them opportunistic infections (infections that do not ordinarily affect those with efficient immune defenses).

These conditions were observed not only in male homosexuals, but also in intravenous drug users and hemophiliacs, suggesting that transmission was related to blood as well as to sexual activity. An infective cause seemed likely and, in 1984, French and American researchers identified the virus responsible. It was named LAV (lymphadenopathy-associated virus) by the French, and HTLV III (human T-cell lymphotropic virus, type III) by the Americans. In 1986, the virus was renamed HIV 1; a similar virus, HIV 2, has been found to be the cause of some cases of AIDS in Africa.

The Effects of HIV

The outer membrane of HIV is coated with a molecule called glycoprotein gp120. This recognizes and binds to molecules on the surface of a type of white blood cell called a helper T-cell (or T4-lymphocyte, or CD4-lymphocyte), which is involved in the immune response. Once bound, the membrane of the virus dissolves into that of the cell, and the virus's contents are absorbed.

Like other viruses, HIV reproduces by inserting its genes into the host cell. These change the way the cell functions, causing it to manufacture many identical copies of the virus. The new viruses then bud out from the cell surface to infect other cells. Helper cells infected with HIV are unable to divide, and eventually die. As a result of changes in their membranes during infection, they stick to uninfected helper cells, forming small clumps of cells that no longer function.

Helper cells normally play a crucial role in the regulation of the immune response. One of their most important functions is to stimulate the activity of cells called killer T-lymphocytes, which normally recognize and destroy virus-infected cells. Because HIV infects and damages the helper cells, it disarms the body's main line of defense against the virus, and renders the body defenseless against a range of other infections and cancers.

Symptoms of AIDS

The features of full-blown AIDS include: cancers, such as Kaposi's sarcoma and lymphoma of the brain; autoimmune diseases, especially thrombocytopenia; and various infections, such as pneumocystis pneumonia (the principal cause of death), severe cytomegalovirus infection, toxoplasmosis, diarrhea caused by cryptosporidium or isospora, candidiasis, disseminated strongyloidiasis, cryptococcosis, and chronic or persistent herpes simplex.

Transmission

HIV has been isolated from blood, semen, saliva, tears, nervous system tissue, breast milk, and female genital tract secretions. However, only semen and blood have been shown to transmit infection.

The principal modes of transmission are sexual contact (penis to anus, vagina, or mouth), blood to blood (via transfusions or needle sharing in drug users), and mother to fetus. Other rare methods are through accidental needle injury, artificial insemination by donated semen, and organ transplant operations.

In Western countries, AIDS is most common among homosexual men. Worldwide, however, heterosexual transmission is the most common way that people become infected. In Africa, AIDS affects men and women equally, probably because the high rate of other sexually transmitted diseases (such as chancroid) increases the rate of HIV transmission by heterosexual sex. As of December 1996, there had been more than 8 million cases of AIDS worldwide, resulting in 6 million deaths. It was estimated that approximately 750,000 individuals in the United States and 23 million individuals throughout the world were infected with HIV. AIDS had become pandemic, with more than 90 percent of HIV infections occurring in developing countries. Sub-Saharan Africa accounted for more than 60 percent of all infections, and in some regions of the continent almost one-third of the inhabitants were infected. Another area of high incidence was South and Southeast Asia, where roughly 20 percent of global cases occurred.

Outlook

Research is continuing into the development of vaccines and new drugs, and scores of compounds are being tested in the laboratory and in clinical trials. For the foreseeable future, however, prevention will remain the key strategy. Health education and the use of safer-sex techniques have had some impact in slowing the rate of growth of the epidemic, but the total numbers of people infected with HIV worldwide were, in the early 1990s, in excess of 20 million.

Efforts aimed at public awareness have been propelled by community-based organizations such as Project Inform and Act-Up, which provide current information to HIV-infected individuals and to individuals at risk for infection. Public figures and celebrities who are themselves HIV infected or who have died from AIDS-including American basketball player Magic Johnson, American actor Rock Hudson, American diver Greg Louganis, and American tennis player Arthur Ashe-have personalized the disease of AIDS and thereby helped society come to terms with the enormity of the epidemic. As a memorial to people who have died from AIDS, especially in the early years of the epidemic, friends and families of AIDS victims stitched together a giant quilt in which each panel of the quilt was dedicated to the memory of an individual who died from AIDS. This quilt has traveled on display from community to community to promote AIDS awareness.

The U.S. government has also attempted to assist HIV-infected individuals through legislation and additional community-funding measures. In 1990 HIV-infected people were included in the Americans with Disabilities Act, making discrimination against people with AIDS for jobs, housing, and other social benefits illegal. Additionally, the Ryan White Comprehensive AIDS Resources Emergency Act established a community-funding program designed to assist in the daily lives of people living with AIDS. This congressional act was named in memory of a young man who contracted HIV through blood products and became a public figure for his courage in fighting the disease and community prejudice. The act is still in place, although continued funding for such social programs is threatened by opposition in the U.S. Congress.

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