DETERMINATION OF IGG1 AND IGG3 SUBCLASSES OF RED BLOOD CELL ANTIBODIES: AN IMPORTANT TOOL FOR PREDICTING IMMUNE MEDIATED HEMOLYTISIS

Abstract

Objectives: Red blood cell (RBC) antibodies of the IgG class can lead to hemolysis in patients depending on many factors, including the IgG subclass. IgGs, particularly IgG1 and IgG3-coated RBCs (red blood cells) are quickly recognized for phagocytosis leading to a greater potential for RBC destruction. The objective of this study is to correlate the presence of IgG1 and IgG3 subclasses with the risk of hemolysis in the context of RBC alloantibodies and autoantibodies. Methods: Blood donors and patients presenting with positive polyspecific direct antiglobulin test (DAT) (Bio-Rad, Cressier, LISS/Coombs card, ref. 004017) were recruited for a 2-month study at a tertiary hospital. All selected donors and patients were further tested with monospecific DAT gel cards (Bio-Rad, Cressier, DC Screening I card with anti-IgG, -IgM, -IgA, -C3c, -C3d, ref. 004857), DAT IgG-dilution (Bio-Rad, Cressier, ref. 004033), which indicates the amount of IgG bound to RBCs, and DAT IgG1/IgG3 (Bio-Rad, Cressier ref. 004043), which further differentiates the IgG1 and IgG3 subclasses. Monocyte monolayer assay (MMA) was performed in select cases with RBC IgG autoantibodies and the results were expressed in terms of monocyte index (MI). Results: A total of 42 patients presented positive monospecific DAT indicating IgG and were included in the study. Of these, 4 (9.5%) were newborns (NB). The other patients (n = 38) presented with a positive DAT. The patient eluates revealed either irregular antibodies with the same specificity as detected in irregular antibody screening and identification, suggesting recent incompatible transfusions (n = 9, 21.4%), or IgGs with panagglutination (n = 29, 69%). A total of 68 donors presenting a positive polyspecific DAT were selected and of these, 27 confirmed positive monospecific DAT with IgG and were included in the study. Of the included NBs (n = 4), IgG1 and IgG3 were not detected in all cases and C3d was also absent on RBC membrane. Nine patients had positive DAT and irregular antibodies on the RBC membrane. None of the patients had been recently transfused in the reference center, suggesting incompatible transfusions in other health services and serological transfusion reactions. None of the involved antibodies were IgG1 or IgG3. Only one case (anti-Jkb) had concomitant C3b on the RBC membrane. Of the 29 patients presenting with autoantibodies of IgG class, 15 (51.7%) presented with either IgG1 or IgG3 and 14 (48.3%) had neither IgG1 nor IgG3. C3d was concomitant in 7 (46.7%) patients with IgG1 or IgG3 and in 3 (21.4%) patients without IgG1 or IgG3. Among the 27 blood donors presenting with IgG autoantibodies, 26 (96.3%) did not present with either IgG1 or IgG3. A striking statistical significance was observed when the frequency of IgG1 and IgG3 was compared between donors and patients (p 5%) monocyte index (MI) was 83.3% versus 33.3%. The p value was 0.07, reflecting the restricted sample size. Conclusions: The determination of the subclass of IgG might be a helpful tool in laboratory practice, because the absence of IgG1 and IgG3 can rule out overt hemolysis and clinical anemia. Donors with positive DAT and autoantibodies of non-IgG1 and non-IgG3 subclasses do not need specific follow-up. On the contrary, donors with IgG1 or IgG3 autoantibodies (uncommon) should be referred to clinical counseling.