Immunoglobulin G (IgG) autoantibodies of 20 patients with autoimmune hemolytic anemia (AHA) were used in immunoaffinity assays with surface-radioiodinated human red was not seen in the absence of p34, and both proteins are likely to be members of the Rh family. Indeed, a 34-kD polypeptide band and 37-55-kD polydisperse "smear," isolated concurrently from the same labeled RBCs by IgG allo-anti-e, were indistinguishable from their autoantibody-isolated counterparts and may well be the same protein identified at different epitopes by the auto-and allo-antibodies. Individual AHA patients' autoantibodies isolated p34 and gp37-55, alone or in combination with band 3 (nine cases); strong band 3 alone (five cases); and combinations of band 3 with GPA (six cases). The autoantibodies of three additional patients whose AHA had been induced by a-methyldopa also isolated p34 and gp37-55. (J. Clin. Invest. 1993. 91:1672-1680

In our initial immunochemical study of the red blood cell (RBC) membrane proteins targeted in 20 cases of warm-antibody autoimmune hemolytic anemia (AHA), RBC eluates of 6 patients mediated immunoprecipitation (IP) of both band 3 and glycophorin A (GPA). This dual IP pattern had previously been observed with murine monoclonal antibodies (MoAbs) against the high frequency blood group antigen, Wrb (Wright), suggesting that the Wrb epitope may depend on a band 3-GPA interaction. Earlier, anti-Wrb had been identified serologically as a prominent non-Rh specificity of AHA autoantibodies. In the present study, 6 autoantibody eluates immunoprecipitating band 3 and GPA from common Wr(b+) RBCs were retested, in parallel with murine anti-Wrb MoAbs, against very rare Wr(a+b-)En(a+)RBCs. One patient's autoantibodies were unreactive with the Wr(b-) RBCs by either IP or indirect antiglobulin test (IAT) and were judged to have “pure” anti- Wrb specificity. Two other patients' autoantibodies displayed both IP and serologic evidence for anti-Wrb as a major component in combination with one or more additional specificities. However, among 3 other patients whose autoantibodies coprecipitated band 3 and GPA, there was no reduction in IP or IAT reactivity with Wr(b-) RBCs in 2 and only slight reduction in the third. We conclude (1) that human anti-Wrb autoantibodies, like their murine monoclonal counterparts, coprecipitate band 3 and GPA from human RBCs; but (2) that not all antibodies with this IP behavior have anti-Wrb serologic specificity, as defined by this donor's Wr(b-) RBCs. The possibility of an additional (non-Wrb) RBC epitope dependent on a band 3-GPA interaction is raised.