Radioimmune assay for the Xg(a) surface antigen at the individual red cell level

An indirect radioimmune assay has been successfully used for the detection of the Xg(a) antigen on the surface of individual human red blood cells. The assay requires only microvolumes of reagents, is highly sensitive, and is equally reliable with fresh blood samples and with red blood cells stored in liquid nitrogen. The method has been used to estimate the number of Xg(a) binding sites. It may be useful to screen for quantitative isoalleles, as well as to investigate the alleged lack of participation of the Xg-locus in the inactivation of the X-chromosome.