Fy³ and S1^a are carried on different red cell membrane proteins

Fy³ and S1^a are high-incidence antigens that are absent from the red cells of 60–70 percent of black individuals. The corresponding antibodies have similar serologic characteristics. Therefore, a study was undertaken to investigate whether Fy³ and S1^a might be the same antigen. Red cells from donors shown to be Fy³ +, S1(a +) were labeled with ¹²⁵I and detergent solubilized. The solubilized membranes were immunoprecipitated with two examples of anti-S1^a and four examples of anti-Fy³. The eluates were run on polyacrylamide gels under reducing or nonreducing conditions. The four examples of anti-Fy³ precipitated a protein of approximately 31 kDa, while the two examples of anti-S1^a exhibited a band at 220 kDa. Since the molecular weight of Fy³ is similar to that reported for Fy^a, it is likely that Fy³ is carried on the same protein that expresses Fy^a and Fy^b. However, Fy³ is distinct from the S1^a antigen, which is known to be carried on complement receptor one (CR1). Immunobematology 1993;9:50–52.