An Autoantibody with Activity Dependent on Red Cell Age in the Serum of a Patient with Autoimmune Haemolytic Anaemia and a Negative Direct Antiglobulin Test

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Abstract
A red cell IgM autoantibody with anti-e specificity was identified in the serum of a rhesus-negative (rr) patient presenting with haemolytic anemia and a negative direct antiglobulin test. The autoantibody strongly agglutinated normal allogeneic rhesus-negative (rr) red cells in saline at 37.degree. C but had only weak activity for autologous red cells. Incubation of the patient''s serum with subpopulations of normal allogeneic red cells obtainedby density fractionation, demonstrated that the strong agglutinating activity of the autoantibody was for red cells with density greater than 1.090 g/ml. Young red cell subpopulations of lower density gave weak reactions and low titration scores equivalent to those obtained with autologous red cells during the haemolytic episode. The patient''s red cells during remission however, when the patient''s haemoglobin level had returned to normal were strongly agglutinated by serum samples taken during the haemolytic episode; as was the case with normal allogeneic red cells, the strong activity was for patient red cells with density greater than 1.090 g/ml, red cell populations of lower density giving low titration scores. The findings in this case indicate that the patient''s red cells which had survived haemolysis during the haemolytic episode were young red cells (density < 1.090 g/ml), the weak sensitivation of these cells being insufficient to cause their destruction by macrophages. Furthermore, these findings, together with observations that IgG autoantibodies may also bind less strongly to young red cells [Gray et al., Br. J. Haemat., 55: 335-345, 1983; Branch et al., Blood 63: 177-180, 1984], imply that quantitative assays of cell-bound antibody during haemolytic episodes may provide an erroneous measure of the red cell antibody load required to effect in vivo haemolysis.