The dynamics of red cell chimaerism in histoincompatible parabiosed mice

A new technique for the quantitation of isoenzymes was applied to assess the proportions of red cells in the circulation of parabiosed mice. Two parent-F1 hybrid combinations showing phosphoglucose isomerase polymorphism were examined at successive stages of parabiosis and after separation. Once red cell populations became mixed, 3 days after union, the ratio of red cell phenotypes was never significantly different from one partner to the other, although parental red cells became predominant after about 20 days. However, F1 hybrid red cells could always be detected. After separation of parabiosed mice there was a return to the original composition although this took longer than would be expected on the basis of reported red cell life span. Packed cell volume measurements indicated that a parental polycythaemia and F1 hybrid anaemia developed in one strain combination but not in the other. Evidence was adduced to support the hypothesis of a difference in red cell flux being responsible for the generation of this polycythaemia-anaemia.