V3 loop

The third variable loop or V3 loop is a part or region of the Human Immunodeficiency Virus. The V3 loop of the viron's envelope glycoprotein, gp120, allows it to infect human immune cells by binding to a cytokine receptor on the target human immune cell, such as a CCR5 cell or CXCR4 cell, depending on the strain of HIV.

This article was abstracted from Wikipedia's Human Immunodeficiency Virus article, subsection on "Replication cycle: Entry to the cell".