NK1.1, a member of the NKR-P1 family of cell surface receptors, is a type II integral membrane glycoprotein with a C-type lectin domain. It is expressed as a disulfide-linked homodimer on all NK cells as well as subsets of thymocytes and peripheral T lymphocytes in selected strains of mice (e.g., C57BL/6, NZB, and CE). NK1.1 mediates cellular activation and differentiation, and is thought to have a particular role in generating Th2 cells. This product does not react with NK cells of BALB/c mice.