How does HIV infect immune cells?
HIV binds to two types of immune cells, lymphotropic and macrophage-tropic, both of which have CD4 receptors. B and helper T-cells (the lymphotropic type) also have CXCR4 co-receptors, and amoebid immune cells (the macrophage-tropic type) have CCR5 co-receptors. If a person has homozygously deficient CCR5 receptors, he/she is usually protected from infection (by HIV-1, the macrophage-tropic strain) because the virus cannot bind to the individual’s macrophage cells. If heterozygous, he/she is typically a slow progressor. A protein on the coat of HIV called Glycoprotein 120 (gp-120) attaches to one of the cell’s receptors, (CD4, CXCR4, or CCR5, depending on the type of cell) and another viral protein, gp-41, allows the virus to fuse with its plasma membrane. After entering the cell, HIV converts one of its 2 strands of RNA (the other is for back-up) into DNA by reverse transcription. The virus enters the cell’s nucleus and the cell’s DNA with integrase, a viral enzyme, and the cell is fo
