Affects
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.