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Skip Navigation U.S. Department of Health and Human Services
Agency for Healthcare Research Quality
Understanding Your Body

The Immune System and HIV

The body's health is defined by its immune system. White blood cells called lymphocytes (B cells and T cells) protect the body from "germs" such as viruses, bacteria, parasites, and fungi. When germs are detected, B cells and T cells are activated to defend the body. However, when the human immunodeficiency virus (HIV) enters the body, it infects special T cells, where the virus grows. The virus kills these cells slowly. As more and more of the T cells die, the body's ability to fight infection weakens, and the person with HIV infection becomes vulnerable to other infections such as tuberculosis and hepatitis C. Individuals are said to have AIDS (acquired immunodeficiency syndrome) when they are sick with serious illnesses and infections that can occur late in HIV infection, when few T cells remain.

The image is a diagram of a Lymphocyte cell and a Human Immunodeficiency Virus (HIV) cell

How Is HIV Transmitted?

Among adults HIV is commonly transmitted during sexual intercourse with an infected partner. During intercourse the virus can enter the body through the linings of the vagina, vulva, penis, rectum, or, rarely, via the mouth after oral sex. HIV can also be transmitted by contact with infected blood, for example, by sharing needles or syringes contaminated with minute quantities of blood containing the virus.

Nearly all HIV-infected children get the virus from their mothers before or during birth. The virus may also be passed from an HIV-infected mother to her infant during breastfeeding.

Who Is Affected?

All population groups are affected by HIV. However, minorities are more affected than others. Four of every 10 HIV patients are black and nearly 1 in 5 is Hispanic.

How Is HIV Infection Treated?

HIV infection is typically treated with a combination of antiviral drugs. These powerful drugs do not cure HIV infection or AIDS. They can suppress the virus but cannot completely eliminate HIV from the body. Thus, people being treated with antiviral drugs can still transmit HIV infection to others through unprotected sex and needle sharing.

Owing to the benefit of antiviral drugs, people with HIV infection may remain healthy for many years.

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