TER-119 is a monoclonal antibody that specifically binds to the Ly76 protein associated with erythroid cells in mice. Ly76 is a glycophorin A-associated protein that is expressed from early proerythroblasts to mature erythrocytes, but not on BFU-E or CFU-E. The TER-119 antibody is commonly used in flow cytometry to identify and exclude red blood cells, allowing for more accurate analysis of other blood cell types, such as in immune cell typing or hematopoietic progenitor studies. In research, the TER-119 antibody helps to distinguish between different stages of red blood cell development. For example, by combining TER-119 with other cell surface molecular markers such as CD71 and CD44, erythroid cells in mouse bone marrow can be differentiated into five stages, including proerythroblasts, basophilic erythroblasts, polychromatophilic erythroblasts, orthochromatic erythroblasts, and mature red blood cells. Additionally, the TER-119 antibody is used to study regulatory mechanisms in the process of erythropoiesis, such as the regulation of CD71+TER119+ erythroid progenitor cells by CD45.