PETRA: Module 1, Chapter 2

What Happens After HIV Infects Cells?

Once HIV enters the body, it replicates rapidly and spreads widely. Two to four weeks after exposure, most HIV-infected people suffer flu-like symptoms, as their immune systems fight off the initial HIV infection. This first immune response may dramatically reduce HIV levels (5). As a result, the number of CD4+ T-cells in a person' body may rebound after the first, acute infection, and may even approach their original levels. The HIV+ person may then remain free of HIV-related symptoms for years.

Meanwhile, however, the virus continues replicating in the organs and tissues of the body's lymphatic system, which is the system that produces, stores, and carries white blood cells to fight infection and disease. These organs and tissues include the spleen, thymus, lymph nodes, tonsils, and adenoids (5). While HIV is confined to a person's lymphatic system, it may not be readily detectable in his or her blood. Ultimately, though, the accumulated HIV overwhelms the person's system, and large quantities of virus enter the bloodstream.

Why do HIV infections almost always progress to AIDS?

1. HIV ELUDES the immune system, so that the body stops fighting it.

Although the body's immune system is usually strong enough to wipe out most viral infections, it cannot fight what it cannot detect. HIV is a fast-mutating virus, meaning that its genetic make-up changes often. HIV's many mutations make some of its particles invisible to the body's immune system, so that they continue to replicate and cause damage. HIV can also hide in the genetic material of an infected cell, where it is shielded from the immune system's radar.

2. HIV DAMAGES the immune system, so that the body can't fight it.

During HIV’s lifecycle, CD4+ cells change, get damaged, and die. Over time, there are not enough healthy CD4+ cells to defend the body. Without enough CD4+ cells, the body's immune system is unable to defend itself against many infections (5). When the immune system is so weak that it can no longer defend against opportunistic infections, a person is said to have Acquired Immune Deficiency Syndrome, or AIDS.

References:
1. Chin. J. (Ed.) Communicable Diseases Manual, 17th Edition. Washington, DC: American Public Health Association, 2000.

2. Mayer, K.H. & Pizer, H.F. The Emergence of AIDS. The Impact on Immunology, Microbiology, and Public Health. Washington, DC: American Public Health Association, 2000.

3. National Institutes of Allergy and Infectious Diseases (NIAID). HIV Infection and AIDS: An Overview. National Institutes of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services, October 2003. Retrieved on January 14, 2004 from http://www.niaid.nih.gov/factsheets/hivinf.htm.

4. Institutes of Allergy and Infectious Diseases (NIAID). How HIV Causes AIDS. National Institutes of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services, October 2001. Retrieved on January 14, 2004 from http://www.niaid.nih.gov/factsheets/howhiv.htm.

5. Pieribone, D. The HIV Life Cycle. ACRIA Update 12(1), Winter 2002/2003. Retrieved on January 26, 2004 from http://www.thebody.com/cria/winter03/hiv_lifecycle.html.

6. GlaxoSmithKline. How HIV Works in Your Body. 2001. Retrieved on January 26, 2004 from http://www.thebody.com/glaxo/howhiv/howhiv.html.