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NK1.1/CD161, also known as KLRB1 or NKR-P1A, is a type II transmembrane C-type lectin-like receptor expressed as a disulfide-linked homodimer on the cell membrane. It is predominantly found on the majority of natural killer （NK） cells and subsets of peripheral T cells, including both CD4+ and CD8+ T cells, particularly those with a "memory" antigenic phenotype. The expression of CD161 is specifically upregulated by IL-12 and is associated with the cytotoxic function of CD16+ NK cells. Functionally, CD161 plays a role in modulating the activation and proliferation of NK cells, inducing interferon-γ production, and releasing cytotoxic granules. When CD161 binds to its ligand LLT1, it inhibits NK cell cytotoxicity and cytokine secretion.