Rabbit CTLA-4 (Cytotoxic T-Lymphocyte–Associated Protein 4, also known as CD152) is an immune checkpoint receptor belonging to the immunoglobulin superfamily that functions as a key negative regulator of T-cell activation in rabbits (Oryctolagus cuniculus). CTLA-4 is primarily expressed on activated CD4⁺ and CD8⁺ T lymphocytes and on regulatory T cells (Tregs) following antigen stimulation. It binds 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. Engagement of CTLA-4 transmits inhibitory signals that suppress T-cell proliferation, cytokine production, and immune activation, thereby helping maintain immune homeostasis and peripheral tolerance. In rabbits, CTLA-4 plays an important role in regulating immune responses to viral and bacterial infections, as well as controlling inflammatory and immune-mediated processes. Because rabbits are widely used as experimental models for immunology and inflammatory disease, rabbit CTLA-4 has been studied in models of autoimmune disease and transplant immunology, where modulation of CTLA-4 signaling helps researchers understand immune checkpoint regulation, T-cell tolerance, and therapeutic strategies for controlling immune-mediated pathology.