Human immunodeficiency virus (commonly known as HIV, and formerly known as HTLV-III and lymphadenopathy-associated virus) is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. It also directly and indirectly destroys CD4+ T cells. As CD4+ T cells are required for the proper functioning of the immune system, when enough CD4+ T cells have been destroyed by HIV, the immune system functions poorly, leading to the syndrome known as AIDS. HIV also directly attacks organs, such as the kidneys, the heart and the brain leading to acute renal failure, cardiomyopathy, dementia and encephalopathy. Many of the problems faced by people infected with HIV result from failure of the immune system to protect from opportunistic infections and cancers.