AIDS is an acronym for acquired immunodeficiency syndrome, a disease characterized by the slow demise of the body's immune system. The agent thought to cause AIDS is the human immunodeficiency virus, commonly called HIV. The terms AIDS and HIV are not synonymous. AIDS refers to the end stages of an HIV infection, stages that are characterized by the presence of certain diseases. A diagnosis of AIDS means that a person has HIV, plus either one or more of 26 opportunistic infections or a T-cell count below 200 per cubic millimeter (mm3). (T cells are the cells that mediate immunity.)
To understand AIDS and its impact on the body, it is necessary to understand the immune system and how HIV interrupts the role of this system in disease prevention. As the name suggests, the immune system is not a single structure that protects the body from disease. Rather, it is the functions of many cells, organs, and processes acting collectively to protect the body from a host of threats that can cause disease.
All living organisms are continuously exposed to substances that are capable of causing them harm. Most organisms protect themselves against such substances in more than one way—with physical barriers, for example, or with chemicals that repel or kill invaders. Man has not only these types of general protective mechanisms, but also a more advanced protective system that is referred to as the immune system. The immune system is a complex network of organs containing cells that recognize pathogens, or infectious agents, and destroys them. The term pathogen is a broad one that is used to denote a disease-causing substance. Common pathogens usually fall into one of three categories: bacteria, viruses, or funguses and parasites. (Perazella, M. et al., 1994)......................
