Transmembrane glycoprotein expressed by T-cells and natural killer (NK) cells and their precursors (PubMed:7506726). Plays a costimulatory role in T-cell activation upon binding to its ligand K12/SECTM1 (PubMed:10652336). In turn, mediates the production of cytokines such as IL-2 (PubMed:1709867). On resting NK-cells, CD7 activation results in a significant induction of interferon-gamma levels (PubMed:7506726). {ECO:0000269|PubMed:10652336, ECO:0000269|PubMed:1709867, ECO:0000269|PubMed:7506726}. This is the function of CD7 (CD7 molecule, ENSG00000173762).