Transfusion Medicine Division, The Johns Hopkins Hospital, United States
Background/Case Studies: Antibodies directed against human leukocyte antigens (HLA) often interfere in pre-transfusion testing. Chloroquine diphosphate treatment (CDP) of red blood cells (RBC) may be used to confirm or remove reactivity attributable to HLA antibodies but has also been reported to weaken antigens from other blood group systems. We evaluated CDP treatment of RBC to remove HLA antigens and its effect on blood group antigen expression.
Study
Design/Methods: Plasma from two patients with known anti-Bga and an HLA antibody of undetermined specificity (anti-HLA), were used to screen reagent and donor RBC by column agglutination test (CAT) to identify RBC expressing HLA. Positive RBCs were incubated with 16% CDP (Immucor, Norcross, GA) for up to two hours at room temperature and retested with patient plasma at 1- and 2-hour intervals by CAT
Results/Findings: Five HLA positive RBC (2 Bg(a+) and 3 HLA positive) were identified by screening. All CDP treated RBC were non-reactive with anti-Bga and anti-HLA after 1-hour and 2-hour incubation. When tested with sera containing non-HLA antibodies, all CDP treated RBC that were positive for respective allogeneic antigens remained reactive after 1-hour and 2-hour incubation, confirming unaltered antigen expression. Unexpected positive reactivity was seen with 3 non-HLA antibody samples (anti-c, anti-Fya and anti-S) in CAT when tested against antigen negative CDP treated RBCs (untreated RBC were non-reactive). The unexpected reactivity was not detected in STT for one sample (anti-Fya), suggesting non-specific reactivity related to CAT. Reactivity with CDP treated RBCs was detected at RT, 37ºC and AHG by STT for the other two samples (anti-S, anti-c); however, untreated RBCs remained non-reactive. Incubation at 4ºC with untreated RBC and cord RBC identified anti-I specificity. RESt adsorption removed the reactivity at RT and 37ºC and weakened the reactivity at AHG with the CDP treated RBC.
Conclusions: These results support the use of CDP remove HLA from RBC; however, CDP treatment may have the potential to enhance cold autoantibody reactivity. Enhancement of cold autoantibodies may interfere with identification of HLA antibodies and complicate antibody identification. Further evaluation is needed to confirm these observations.
