Evidence that the low frequency antigen Orriss is part of the MN blood group system

The low frequency antigen Orriss (Or) was found on the erythrocytes of a healthy blood donor. A subsequent family investigation showed Or to segregate independently of the Rh, Colton and Kidd blood group systems; however, it appeared to be inherited with the Ms gene complex. Studies carried out demonstrated that sialoglycoproteins (SGPs) extracted from Or+ erythrocytes specifically neutralize anti-Or and that all Or+ individuals tested carry an M antigen which is more resistant to trypsin treatment than the M antigen of Or- erythrocytes. These results lead to the conclusion that the Or antigen is found on a variant alpha-SGP and its presence renders this molecule more resistant to trypsin than normal.