CD160, also known as NK1, BY55 or NK28, is a 181 amino acid lipid-anchored cell membrane glycoprotein that contains one immunoglobulin-like domain. Expressed in small intestine, spleen and functional NK (natural killer) and T cytotoxic lymphocytes, CD160 exists as a disulfide-linked homomultimer that functions as a receptor for MHC (major histocompatability complex) molecules and is thought to regulate the function of NK cells. Additionally, CD160 interacts with HVEM (herpesvirus entry mediator) and, via this interaction, is able to negatively regulate CD4+ T cell activation, indicating a role in immune system regulation. Multiple isoforms of CD160 exist due to alternative splicing events. The gene encoding CD160 maps to human chromosome 1, which spans 260 million base pairs, contains over 3,000 genes and comprises nearly 8% of the human genome.