CD200R1 (CD200 Receptor 1) is a cell surface glycoprotein belonging to the immunoglobulin superfamily, primarily expressed on immune cells such as macrophages, dendritic cells, and T lymphocytes. It interacts with its ligand CD200. a membrane-bound protein expressed on various tissues, to modulate immune responses by delivering inhibitory signals. This interaction plays a critical role in maintaining immune homeostasis, dampening excessive inflammation, and promoting tolerance, particularly in contexts like autoimmune diseases, transplantation, and cancer. Structurally, CD200R1 contains two extracellular immunoglobulin-like domains, a transmembrane region, and a cytoplasmic tail with signaling motifs that recruit phosphatases (e.g., SHP-1/2) to suppress activating signals. CD200R1 antibodies are tools or therapeutics designed to either block or mimic the CD200-CD200R1 axis. In research, they are used to study immune regulation mechanisms, while clinically, antagonistic antibodies aim to enhance anti-tumor immunity by disrupting immunosuppressive CD200 signaling. Conversely, agonistic antibodies may treat inflammatory disorders by amplifying inhibitory pathways. These antibodies also serve as diagnostic reagents for detecting receptor expression via flow cytometry or immunohistochemistry. Their development highlights the therapeutic potential of targeting immune checkpoint pathways to balance immune activation and tolerance.