Human immunodeficiency virus (HIV) is a virus that destroys the immune system. HIV targets CD4 cells, or helperT cells, which are cells in your blood that help the body fight disease. Over many years, the CD4 cells are destroyed. The body then has a weaker defense against infections such as lung infections, mouth infections and eye infections. Some forms of cancer, such as lymphoma or cervical cancer, may also occur. When infections and other problems occur as a result of the loss of CD4 cells, the person is said to have "acquired immunodeficiency syndrome" (AIDS).