While more research is needed to confirm the sequence, it is believed that the gp120 molecule on the HIV unites, via the V3 loop, with the CD4 molecule on the T-lymphocyte, macrophage, or brain cell.
The gp120 then changes shape, drops down, and binds with the co-receptor.Thus HIV binds twice to the T-lymphocyte or macrophage - once at the CD4 molecule and once at the co-receptor site.
