Differential red blood cell age fractionation and Band 3 phosphorylation distinguish two different subtypes of warm autoimmune hemolytic anemia.

Warm autoimmune hemolytic anemia (wAIHA) is a blood disorder characterized by the increased destruction of autologous red blood cells (RBCs) due to the presence of opsonizing pathogenic autoantibodies. Preliminary reports published more than three decades ago proposed the presence of two wAIHA subtypes: Type I, in which autoantibodies preferentially recognize the oldest, most dense RBCs; and Type II, characterized by autoantibodies that show no preference. STUDY DESIGN AND METHODS: We evaluated patients having wAIHA for Type I and II subtype using discontinuous Percoll gradient age fractionation and direct antiglobulin test (DAT). We performed Western immunoblotting and mass spectrometry to show autoantibody specificity for Band 3. We investigated Band 3 tyrosine phosphorylation in different Percoll fractions to determine aging associated with oxidative stress. RESULTS: We confirm the existence of two subtypes of wAIHA, Type I and Type II, and that autoantibodies recognize Band 3. Type I patients were characterized by five Percoll fractions, with a DAT showing IgG opsonization F1 < F5 and elevated Band 3 phosphorylation compared to healthy controls (HCs). In contrast, Type II wAIHA patients were characterized by three to four Percoll fractions, where the DAT IgG opsonization shows F1 ≥ F3/4 and Band 3 phosphorylation was absent or significantly decreased compared to HC. CONCLUSIONS: Type I patients have increased Band 3 tyrosine phosphorylation that may represent accelerated aging of their RBCs resulting in exacerbation of a pathologic form of RBC senescence. Type II patients show decreased Band 3 tyrosine phosphorylation and lack the oldest, most dense RBCs suggesting premature RBC clearance and a more severe wAIHA.

Western immunoblotting as a new tool for investigating direct antiglobulin test-negative autoimmune hemolytic anemias.

BACKGROUND: Direct antiglobulin test-negative (DAT(-)) autoimmune hemolytic anemia, characterized by hemolysis without detectable immunoglobulin or complement on patient red blood cells (RBCs), poses a diagnostic challenge. To select therapy, classification of the hemolysis as immune- or non-immune-mediated is important. We developed a method using Western immunoblot (WB) to classify DAT(-) patients by measuring and comparing levels of RBC immunoglobulin (Ig)G to normal donors. STUDY DESIGN AND METHODS: RBC samples from 42 normal donors were made into ghosts and analyzed by WB and densitometry to establish a normal mean relative quantity of IgG (RQIgG) on the RBCs. RQIgG on eight DAT(-) and eluate-negative patients with hemolytic anemia was determined and compared to RQIgG on normal RBCs. RESULTS: RQIgG of 42 normal donors indicated a calculated mean ± SD of 0.0016 ± 0.0015 and we used a cutoff of 0.0047, the mean + 2SD. This was compared with a receiver operating curve cutoff of 0.0041 with 100% sensitivity and 93% specificity. Of the eight patients tested, three were classified as non-immune-mediated (one had pyruvate kinase deficiency) and five as immune-mediated. Two of the patients in the latter group underwent splenectomy, followed by remission. CONCLUSION: WB analysis is more sensitive than conventional test tube DAT or elution analysis. Our assay confirms: 1) previous studies showing normal RBCs are sensitized with IgG, perhaps due to natural autoantibody to senescence; 2) that some normal RBCs have increased levels of IgG without signs of disease; and 3) that WB distinguishes between non-immune- and immune-mediated hemolytic anemia in DAT(-) patients and may be useful for clinical diagnosis.