HIV is a single strand RNA virus, belongs to retrovirus family, lentivirus subfamily, HIV is divided into HIV-1 type and HIV-2 type, AIDS around the world is mainly caused by HIV-1 type, HIV-2 type is endemic in West Africa. HIV-1 can be further divided into different subtypes, including the M subtype group (the major subtype group), the O subtype group, and the N subtype group. HIV is a 20-hedral stereosymmetric spherical particle with a spiky glycoprotein on the surface, with a diameter of about 100nm, which is divided into two parts: envelope and core. Outside the core are viral capsid proteins (P24, P17). After the body is infected with HIV, P24 antigen is an early etiological marker that can be detected from the serum. It can be detected about 2 to 3 weeks after infection, and it enters the antigen peak about 1 to 2 months, and then forms antigen-antibody complex with the production of antibodies. Due to the neutralization of antibodies, the concentration of P24 antigen drops to a level that is difficult to detect. Detection of the P24 antigen (viral capsid protein) directly correlates with viral load in the circulating system of an infected individual. The outermost layer of the virus is the envelope, which is embedded with the outer membrane glycoprotein (gp120) and the transmembrane glycoprotein (gp41). The transmembrane protein of HIV-1 is gp41 and the transmembrane protein of HIV-2 is gp36.

HIVp24, gp36 and gp41 are markers of HIV infection. It can be detected within 2-8 weeks of first exposure and has been detected in the blood ever since.