How HIV Affects the Body

HIV is unique in its ability to compromise the immune system. Learn how the disease progresses and makes patients susceptible to serious complications.

Human immunodeficiency virus (HIV) infects the cells of the immune system. In particular, HIV attacks and destroys the T helper lymphocytes, or T-cells, which are crucial to the immune system and immune response. (These cells are also called CD4-positive lymphocytes because HIV uses the protein CD4, present on the surface of the cell, to attach itself and pry its way into the cell.) Each day, your body produces millions of CD4+ T-cells to help maintain your immunity and fight off invading viruses and germs. Once HIV is in your body, the virus is able to copy itself over and over, increasing its ability to kill CD4+ T-cells. Soon, infected cells outnumber healthy T-cells.

The lower a person’s CD4+ T-cell count goes, the more susceptible the person is to viruses and infections that an otherwise healthy body could fight. In the initial stages of the infection, the decline in T-cell count is gradual. The first few months and years after a person is infected, T-cell counts may remain very near normal or only slightly decreased. It’s when T-cell numbers begin to dip dramatically that patients with HIV begin noticing additional, worsening symptoms of the infection.

The Four Stages of HIV

An HIV infection is typically divided into four stages: acute primary infection, clinical latent infection, symptomatic HIV infection, and progression from HIV to AIDS.

Acute Primary Infection

Within the first few weeks of contracting HIV, 70 percent of people will experience flu-like symptoms—fever, headache, upset stomach, and muscle soreness are among the most common initial signs of an HIV infection. A positive diagnosis is possible at this stage, but many will not associate their symptoms with an HIV infection, unaware they have contracted the virus.

During the acute primary infection, HIV-infected cells are circulating throughout the blood system. Your body responds by producing HIV antibodies and cytotoxic lymphocytes (killer T-cells that seek out and destroy invading viruses or bacteria). Two to four weeks after infection, the immune system mounts an attack against the HIV with these antibodies and killer T-cells. HIV levels in the blood will be greatly reduced, and CD4+ T-cell counts rebound slightly.