HIV infection is caused by a dramatic decrease in lymphocytes caused by the HIV virus, which first binds to CD4 cells, mainly helper T lymphocytes, macrophages and Langerhans cells. The other part can become latent in these cells and can be activated under certain conditions to cause the death of these cells again. In the process of multiplication, the HIV virus can also cause dramatic damage to other lymphocytes and natural killer cells, resulting in the collapse of the entire immune system of the patient. Therefore, when AIDS patients really develop, they will have a variety of conditional infections and a variety of tumors.