Blut (1981) 43:361-366 Blut © Springer-Verlag 1981 Immunochemical Properties of Antigens Present on Immature Erythrocytes from Mouse and Rat G. Mouchiroud 1, J. P. Blanchet1, V. Krsmanovic2, and T. Greenland 2 1 D6partementde BiologicG6n6raleet Appliqu6e, Laboratoire associ6an CNRS, Universit6 Claude Bernard Lyon I, 43 Boulevarddu 11 Novembre1918, F-69622 Villeurbanne Cedex, France 2 Units de VirologicINSERM U51, Groupe de RechercheCNRS No 33, F-69371 Lyon Cedex2, France Summary. Rabbit antisera directed against erythrocytes from anemic mice or from newborn rats, once absorbed on homologous normal adult erythrocytes, re- cognize antigens present respectively on immature erythrocytes from anemic adult mice or rats (Im M and Im R antigens). Using iodinated immature erythro- cytes from both species, homologous sera precipitated two populations of anti- gens showing 230,000 D and 95,000 D molecular weights. Im M antigens (230,000 and 95,000 D) were partially precipitated using anti-Im R serum. After total ab- sorption of the sample by anti-Im R serum, both 230,000 and 95,000 D antigens were still immunoprecipitated using anti-Im M serum. Similar results were ob- tained using Im R antigens and anti-Im M serum then anti-Im R serum. This de- monstrates that some Im specificities are common to rat and mouse while others, showing identical molecular weights, are species-specific. Key words: Immunoprecipitation - Immature antigens - Mouse - Rat The maturation of red cells involves many biochemical modifications such as syn- thesis of specific components (e.g. hemoglobin, spectrin) and, in mammals, nucleus extrusion. Many modifications of the red cell membrane have been also reported. In rabbits, proteins found in the reticulocyte membrane are lost during erythrocyte maturation [6, 8] while the density of antigenic sites detected on mature circulating red cells is strongly increased [3,4,11]. By contrast, in humans, HL-A antigens have been shown to disappear from maturing red cells [14]. In the mouse, we have shown that particular antigens were present on circulating immature erythrocytes (Im anti- gens) and disappeared during the final step of erythropoietic differentiation [1]. They are detected both during fetal development and adult life. We have also ob- served similar Im antigens in the chicken ([ 13] and unpublished results). Existence of similar antigenic systems in such foreign species led us to extend our observations to another laboratory animal, the rat, and to compare the immature Offprint requests to: Dr. J. P. Blanchet (address see above) 0006-5242/81/0043/0361/$ 1.20