The mature envelope protein (Env) consists of a homotrimer of noncovalently associated gp120-gp41 heterodimers. The surface protein gp120 (SU) from the human immunodeficiency virus (HIV) attaches the virus to the host lymphoid cell by binding to the primary receptor CD4. The interaction induces a structural rearrangement creating a high affinity binding site for a chemokine coreceptor like C, Xenopus/Amphibian,CR4 and/or CCR5. The gp120 protein is also a ligand for CD209/DC-SIGN and CLEC4M/DC-SIGNR, which are respectively found on dendritic cells, and on endothelial cells of liver sinusoids and lymph node sinuses. These interactions allow capture of viral particles at mucosal surfaces by these cells and subsequent transmission to permissive cells.