In vitro determination of red cell alloantibody significance using an assay of monocyte‐macrophage interaction with sensitized erythrocytes

Abstract

Red cell alloantibodies (148) of specificities generally considered to be of clinical significance, were studied in vitro for their ability to induce phagocytosis of sensitized red cells by allogeneic mononuclear phagocytes. Only 53% of the [human] alloantibodies studied mediated significant phagocytosis in vitro. The percentages for each blood group system were as follows: Kell, 73%; Jka, 32%; JKb, 67%; D, 75%; E, 60%; Fya, 62%; Yta, 25%; Ge,22%; and Vel, 25%. Significant phagocytosis was independent of the strength of the indirect antiglobulin test. The percentage of anti-Jka and anti-Fya mediating significant phagocytosis was increased when fresh complement was added during the sensitization procedure and/or red cells homozygous for the antigen in question were used. The in vivo clinical significance was documented for 9 alloantibodies; 5 caused hemolysis and 4 did not. Those causing in vivo hemolysis mediated in vitro phaocytosis by monocyte-macrophages whereas the antibodies that did not result in hemolysis showed no increased in vitro phagocytosis. Autologous monocytes were more reliable than random allogeneic monocytes in that phagocytosis was increased over that obtained using allogeneic monocyte-macrophages with 2 of 4 alloantibodies having documented clinical significance. The use of target red cells homozygous for the antigen in question, the addition of fresh complement in the antibody sensitization procedure, and use of autologous and allogeneic monocyte-macrophages appear necessary for optimal results. Since 47% of those alloantibodies generally considered to be clinically significant failed to mediate phagocytosis in vitro, the monocyte-macrophage assay should not be considered a predictive assay of a given alloantibody''s in vivo significance or lack of significance until more extensive correlation of these assays with in vivo red blood cell survival is obtained.