Phylogenetic tree of HIV-1 env gene C2-V3 region from Italian B-clade isolates. The C2-V3 env region (position 7001 to 7196 of HIV-1HXB2) of 143 Italian HIV-1 isolates, identified in the whole epidemic, has been aligned to reference sequences of all Group M subtypes, in order to generate the phylogenetic tree by the neighbor-joining method. The BIT indicates the "Italian branch" of the tree, which includes three major clusters B1 – B3. The reliability has been estimated from 1'000 bootstrap replicates. For editorial convenience, only the percentage value for the Italian Branch has been shown. All other values are > 90%.