reticulocyte Jie Zheng Tomasz Adamusiak An immature erythrocyte that changes the protein composition of its plasma membrane by exosome formation and extrusion. The types of protein removed differ between species though removal of the transferrin receptor is apparent in mammals and birds. SNOMEDCT:52802009 NCIt:C12528 An immature erythrocyte showing a basophilic reticulum under vital staining. erythroid lineage cell cell type