ERIK, a low-frequency red cell antigen of the MNS blood group system associated with Sta

A new low-frequency red cell antigen, ERIK (MNS37), is associated with the Sta antigen of the MNS system. Four ERIK+ propositi have been identified: all are St(a+). Thirteen other St(a+) samples, including one of the Mz type, and over 200 St(a-) samples were ERIK-. In two of the propositi ERIK is associated with an abnormal trypsin-resistant M antigen; in the others it is associated with N, which is shown to be expressed weakly in one family. Immunoblotting with an antibody to an epitope common to glycophorin A (GPA) and glycophorin B (GPB) gave identical results with St(a+) ERIK+ and St(a+) ERIK- cells, revealing GPA, GPB, an abnormal structure GPSta and aggregates of these components. In the propositi with trypsin-resistant M, GPSta carries the unusual M antigen, whereas in the M-N+ERIK+ individual analysed by immunoblotting GPSta carries N. Immunoblotting with anti-Sta and anti-ERIK showed that Sta is located on GPSta but that ERIK is located on GPA, presumably the GPA molecule encoded by the GYPA gene contiguous to the gene encoding GPSta.