Page 178 - 84 human physiolofy part-1

Chapter 9

• Vitiligo is an autoimmune disorder in which the immune system destroys pigment-making
cells called melanocytes. This results in irregularly shaped milky-white patches of skin on
different parts of the body. This is the condition which Michael Jackson claims to have.

Immunodeficiency Diseases

When the immune system is presented with foreign antigens in association with dendritic cells, a
vigorous immune response ensues. (Antigens are the molecules on the surface of invader cells that
announce them as different from the body's cells.). Alternatively, dendritic cells can be exploited
during the development of many immune based diseases.

AIDS and HIV

Acquired immunodeficiency disease (AIDS) is a well-known immune system disease. Acquired
Immune Deficiency Syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a collection
of symptoms and infections resulting from the specific damage to the immune system caused by the
human immunodeficiency virus (HIV).The late stage of the condition leaves individuals prone to
opportunistic infections and tumors. Although treatments for AIDS and HIV exist to slow the virus's
progression, there is no known cure. HIV is transmitted through direct contact of a mucous membrane
or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal
fluid, and breast milk.This transmission can come in the form of anal, vaginal or oral sex, blood
transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy,
childbirth, or breastfeeding, or other exposure to one of the above bodily fluids. AIDS is the most
severe manifestation of infection with HIV. HIV is a retrovirus that primarily infects vital components
of the human immune system such as CD4+ T cells (a subset of T cells), macrophages and dendritic
cells. It directly and indirectly destroys CD4+ T cells. CD4+ T cells are required for the proper
functioning of the immune system. When HIV kills CD4+ T cells so that there are fewer than 200
CD4+ T cells per microliter (µL) of blood, cellular immunity is lost, leading to the condition known as
AIDS. Acute HIV infection progresses over time to clinical latent HIV infection and then to early
symptomatic HIV infection and later to AIDS, which is identified on the basis of the amount of CD4+
T cells in the blood and the presence of certain infections.

In the absence of antiretroviral therapy, the median time of progression from HIV infection to
AIDS is nine to ten years, and the median survival time after developing AIDS is only 9.2 months.
However, the rate of clinical disease progression varies widely between individuals, from two weeks up
to 20 years. Many factors affect the rate of progression. These include factors that influence the body's
ability to defend against HIV such as the infected person's general immune function. Older people have
weaker immune systems, and therefore have a greater risk of rapid disease progression than younger
people. Poor access to health care and the existence of coexisting infections such as tuberculosis also
may predispose people to faster disease progression. The infected person's genetic inheritance plays an
important role and some people are resistant to certain strains of HIV.

Different Types of T Lymphocyte Cells

Several different subsets of T cells have been described, each with a distinct function.

178 | Human Physiology