HIV-1 group O was named for “Outlier” group. After the discovery of the virus ANT70 by a group in Belgium(1990), and the further characterization of this isolate, as well as the MVP5180 and VAU isolates(1994) it became clear that a new group of viruses, distinct from the HIV-1 Major (M) group, was present in the human population.
HIV-1 group O patient's sera were only reactive to the Group O-specific V3 and gp41 peptides. This provided the first direct evidence that this patient was infected with a Group O variant.
Gp41, known as glycoprotein 41, is a subunit of the envelope protein complex of retroviruses which includes human immunodefiiciency (HIV).
Gp41 is transmembrane protein that contains several sites within its ectodomain that are required for infection of host cells.
Due to its importance in host cell infection, it has also gained much attention as a potential target for HIV serological test for diagnosis. | 
