Based on the results of current studies, the infection of mammalian cells by HIV-1 involves three main steps: the binding of gp120 to CD4, which changes the conformation of gp120, which allows the glycoprotein to interact with the chemokine co-receptors, CCR5 or CXCR4, on the surface of the mammalian cell. Here, ITIH4 is linked to infection.