UL16-binding protein 1 (ULBP1), UL16-binding protein 2 (ULBP2), UL16-binding protein 3 (ULBP3), UL16-binding protein 4 (ULBP4), UL16-binding protein 5 (ULBP5), UL16-binding protein 6 (ULBP6) (ULBP1, ULBP2, ULBP3, ULBP4, ULBP5, ULBP6)

UL16-binding proteins 1 through 6 are a family of human cell surface glycoproteins structurally related to MHC class I molecules but distinct in lacking the α3 domain and transmembrane segments (ULBP1 is GPI-anchored). They function as stress-induced ligands for the NKG2D receptor on cytotoxic lymphocytes, triggering immune responses against infected, malignant, or otherwise stressed cells. Their expression is often upregulated during viral infection or cellular transformation; viruses such as HCMV may target these ligands to evade immune surveillance, for example via interaction with the viral UL16 glycoprotein to prevent their surface localization. The clinical relevance of these molecules spans cancer prognosis, immune system modulation, and potentially therapeutic targeting or biomarker identification for immune-related diseases.

Other names

NKG2D ligand familyRAET1 familyretinoic acid early transcript 1 family (RAET1E/ULBP4, RAET1L/ULBP6, etc.)

Stimulate cytotoxicity by binding to and activating the NKG2D receptor on natural killer cells, CD8+ T cells, and γδ T cells. Promote immune recognition and clearance of stressed, infected, or transformed cells