Mouse TIM-3 (T cell immunoglobulin and mucin domain-containing protein 3, also known as HAVCR2) is an immune checkpoint receptor that regulates T cell activation, immune tolerance, and inflammatory responses in mice (Mus musculus). TIM-3 is a member of the TIM (T cell immunoglobulin and mucin domain) family of immune regulatory proteins, which includes TIM-1, TIM-3, and TIM-4, molecules that modulate immune activation and help maintain immune homeostasis. In mice, TIM-3 is expressed on activated CD4⁺ and CD8⁺ T lymphocytes, regulatory T cells, natural killer (NK) cells, dendritic cells, and macrophages, where it functions primarily as a negative regulator of immune responses. Interaction of TIM-3 with ligands such as galectin-9, phosphatidylserine, and HMGB1 transmits inhibitory signals that reduce T cell proliferation, cytokine production, and cytotoxic activity, helping to limit excessive inflammation and tissue damage. In murine models, TIM-3 has been widely studied in autoimmune disease, chronic infection, and cancer, including experimental autoimmune encephalomyelitis (a model of multiple sclerosis), chronic viral infection models, and tumor immunology, where TIM-3 expression is associated with T cell exhaustion and immune suppression. Because mice are the most widely used genetic model organism in immunology, characterization of mouse TIM-3 has been critical for understanding immune checkpoint regulation, T cell exhaustion mechanisms, and the development of immunotherapies targeting checkpoint pathways relevant to human disease.