Abstract
BackgroundTypically minor ABO incompatible platelet products are transfused without any incident, yet serious hemolytic transfusion reactions occur. To mitigate these events, ABO ‘low titer’ products are used for minor ABO incompatible transfusions. We sought to understand the role of IgM/IgG and complement activation by anti-A on extravascular hemolysis.MethodsSamples evaluated included (i) Group O plasma from a blood donor whose apheresis platelet product resulted in an extravascular transfusion reaction, (ii) Group O plasma from 12 healthy donors with matching titers that activated complement (N = 6) or not (N = 6), and (iii) Group O sera from 10 patients with anti-A hemolysin activity. A flow cytometric monocyte erythrophagocytosis assay was developed using monocytes isolated by immunomagnetic CD14-positive selection from ACD whole blood of healthy donors. Monocytes were frozen at − 80 °C in 10% dimethyl sulfoxide/FBS and then thawed/reconstituted on the day of use. Monocytes were co-incubated with anti-A-sensitized fluorescently-labeled Group A1 + RBCs with and without fresh Group A serum as a source of complement C3, and erythrophagocytosis was analyzed by flow cytometry. The dependency of IgM/IgG anti-A and complement C3 activation for RBC erythrophagocytosis was studied. Anti-A IgG subclass specificities were examined for specific samples.ResultsThe plasma and sera had variable direct agglutinating (IgM) and indirect (IgG) titers. None of 12 selected samples showed monocyte-dependent erythrophagocytosis with or without complement activation. The donor sample causing a hemolytic transfusion reaction and 2 of the 10 patient sera with hemolysin activity showed significant erythrophagocytosis (> 10%) only when complement C3 was activated. The single donor plasma and two sera demonstrating significant erythrophagocytosis had high IgM (≥ 128) and IgG titers (> 1024). The donor plasma anti-A was IgG1, while the patient sera were an IgG3 and an IgG1 plus IgG2.ConclusionHigh anti-A IgM/IgG titers act synergistically to cause significant monocyte erythrophagocytosis by activating complement C3, thus engaging both Fcγ- and CR1-receptors.
Highlights
Minor ABO incompatible platelet products are transfused without any incident, yet serious hemolytic transfusion reactions occur
Monocytes were co-incubated with anti-A-sensitized fluorescently-labeled Group A1 + red blood cells (RBCs) with and without fresh Group A serum as a source of complement C3, and erythrophagocytosis was analyzed by flow cytometry
Fcγ-receptors present on monocytes/macrophages bind the Fragment crystallizable (Fc) portion of IgG on sensitized RBCs leading to their phagocytosis
Summary
Minor ABO incompatible platelet products are transfused without any incident, yet serious hemolytic transfusion reactions occur. Hemolytic reactions due to minor ABO incompatible transfusions have been documented [1,2,3,4,5,6,7,8,9] and are most often thought to be associated with high titer anti-A/A,B [6]. (2020) 18:216 products, and high titer minor ABO incompatible products have been transfused to patients without clinical impact [6, 7]. Monocytes/macrophages possess complement C3b receptors (CR1) on their surface, which can bind and engulf complement coated RBCs. It has been reported that ABO antibody-dependent complement activation alone is insufficient to cause significant erythrophagocytosis [13,14,15]
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