Bovine CTLA-4 (Cytotoxic T-Lymphocyte–Associated Protein 4, also known as CD152) is an immune checkpoint receptor belonging to the immunoglobulin superfamily that plays a critical role in the negative regulation of T-cell activation in cattle (Bos taurus). CTLA-4 is primarily expressed on activated CD4⁺ and CD8⁺ T lymphocytes and regulatory T cells (Tregs) following antigen stimulation. It functions by binding to the costimulatory ligands CD80 (B7-1) and CD86 (B7-2) on antigen-presenting cells such as dendritic cells, macrophages, and B cells, competing with the activating receptor CD28 for these ligands. Through this interaction, CTLA-4 transmits inhibitory signals that reduce T-cell proliferation, cytokine production, and immune activation, helping to maintain immune homeostasis and prevent excessive inflammation. In bovine immunology, CTLA-4 plays an important role in regulating immune responses to viral, bacterial, and parasitic infections, as well as in controlling immune-mediated inflammation during diseases affecting cattle. Because immune checkpoint pathways are essential for balancing immune activation and tolerance, bovine CTLA-4 is studied in veterinary immunology, infectious disease research, and vaccine response studies, contributing to improved understanding of T-cell regulation and immune modulation in livestock health.