The TER-119 antibody is named for the antigen to which it binds, a 52 kDa surface protein that is associated with glycophorin-A. TER-119 is considered to be a lineage marker for later stages of erythroid cell development, as its expression begins at the pro-erythroblast stage. TER-119 antigen is not expressed at either BFU-E or CFU-E stages, i.e. prior to the pro-erythroblast stage.