Immunoglobulin subtyping and quantification in direct antiglobulin test: positive haemolysis in an HIV-prevalent setting

AIMS

Positive direct antiglobulin tests (DATs) are valuable in identifying the aetiology of autoimmune haemolysis and in guiding therapeutic intervention. However, in HIV-positive individuals with background polyclonal gammopathy, a positive DAT in the absence of haemolysis is common. In this setting, IgG quantification and subtyping may be of value, as this is possible with the recently introduced gel cards. There is paucity of literature evaluating the diagnostic usefulness of IgG subtyping and quantification in HIV-positive individuals who are investigated for autoimmune haemolytic anaemia (AIHA). This study evaluated the usefulness of IgG quantification and subtyping in the diagnostic work-up of AIHA in patients with a positive DAT, with and without HIV infection.

METHODS

This retrospective, cross-sectional study included patients investigated for AIHA in a quaternary care hospital. Those with a positive DAT had their IgG subtyped and quantified using the ID-Card DAT IgG₁/IgG₃ and IgG-dilution cards (Bio-Rad, Cressier, Switzerland).

RESULTS

Ninety patients admitted from December 2019 to March 2020 were investigated for AIHA. Forty-four (49%) patients had a positive DAT of whom 26 (59%) had evidence of haemolysis, and 16 (36%) were HIV positive. Concurrent HIV and haemolysis were present in eight patients, two of whom had IgG₁ although none had an IgG antibody titre >1:30. None of the HIV-positive patients without features of haemolysis had IgG₁/IgG₃ or IgG antibody titres >1:30.

CONCLUSION

In our clinical setting, IgG quantification and subtyping were found to be of limited value in the diagnostic characterisation of AIHA in HIV-positive patients with false-positive DAT.

Serological blind spots for variants of human IgG3 and IgG4 by a commonly used anti-immunoglobulin reagent

BACKGROUND

Human immunoglobulin G (IgG) includes four different subtypes (IgG1, IgG2, IgG3, and IgG4), and it is also now appreciated that there are genetic variations within IgG subtypes (called isoallotypes). Twenty-nine different isoallotypes have been described, with 7, 4, 15, and 3 isoallotypes described for IgG1, IgG2, IgG3, and IgG4, respectively. The reactivity of anti-IgG with different isoallotypes has not been characterized.

STUDY DESIGN AND METHODS

A novel monoclonal anti-K antibody (PugetSound Monoclonal Antibody 1 [PUMA1]) was isolated and sequenced, and a panel of PUMA1 variants was expressed, consisting of the 29 known IgG isoallotypes. The resulting panel of antibodies was preincubated with K-positive red blood cells (RBCs) and then subjected to testing with currently approved anti-IgG by flow cytometry, solid phase systems, gel cards, and tube testing.

RESULTS

A US Food and Drug Administration (FDA)-approved monoclonal anti-IgG (gamma-clone) failed to recognize 2 of 15 IgG3 isoallotypes (IgG3-03 and IgG3-13) and 3 of 3 IgG4 isoallotypes (IgG4-01, IgG4-02, and IgG4-03). In contrast, an FDA-approved rabbit polyclonal anti-IgG recognized each of the known human IgG isoallotypes.

CONCLUSION

These findings demonstrate "blind spots" in isoalloantibody detection by a monoclonal anti-IgG. If a patient has anti-RBC antibodies predominantly of an IgG3 subtype (the IgG3-03 and/or IgG3-13 variety), then it is possible that a clinically significant alloantibody would be missed. IgG-03 and IgG-13 have an estimated frequency of 1% to 3% in Caucasian populations and 20% to 30% in certain African populations. Nonreactivity with IgG4 is a known characteristic of this monoclonal anti-IgG, but IgG4 isoallotypes have not been previously reported.

Haemoglobin levels in autoimmune haemolytic anaemias at diagnosis: relationship with immunoproteins on red blood cells

Previous investigations of the relationship between characteristics of immunoproteins on red blood cells (RBCs) and the occurrence of autoimmune haemolysis yielded divergent results. Here, we studied these characteristics in autoimmune haemolytic anaemias (AIHAs) to determine their relationship with the degree of anaemia at diagnosis. We studied at diagnosis 52 cases of warm AIHA with positive direct antiglobulin test. Immunohaematological testing and determination of immunoglobulin class, complement, and immunoglobulin G (IgG) were performed using gel technology (GCT). Median haemoglobin (Hb) levels significantly differed between cases with IgG1 only or negative for IgG subclasses (7.4 g/dl), those with IgG3 or IgG1 + IgG3 (6.5 g/dl), and those with multiple immunoglobulins (5 g/dl). Logistic regression indicated that IgG3 detection was the only variable significantly related to the occurrence of RBC transfusion in AIHA (odds ratio 4.05, 95 % CI 1.1-14.7). In our study, the type of immunoprotein(s) on the RBC surface was associated with different Hb levels at AIHA diagnosis. IgG3 and multiple immunoglobulins were associated with lower Hb levels; IgG3 was also associated with a higher percentage of patient transfusions in the first week after diagnosis. Thus, qualitative differences in these immunoproteins may lead to deeper and more prolonged anaemia levels, influencing the need for RBC transfusion.

Evaluation of the use of gel card system for assessment of direct coombs test: weighing the pros and cons

A positive direct Coombs test (DCT) is the hallmark of diagnosis of immune hemolytic anemias. The reagent used for the test is the Antihuman globulin (AHG), which may be either 'Polyspecific' or 'Monospecific'. The advent of the Gel card systems has made the procedure and interpretation of DCT simpler. Aim of this study is to evaluate three of the various techniques used for the performance and interpretation of DCT. A total of 96 EDTA samples were included in the study. DCT was performed by (i) polyspecific AHG manual tube method (ii) polyspecific AHG Gel card method and (iii) monospecific AHG (Anti IgG and Anti Complement) manual tube method. In our study we considered positivity by monospecific AHG as the standard for diagnosis. Of the total 96 samples evaluated, 44 cases positive by Gel card method, were also positive for either one or both the monospecific AHG reagents. 17 cases positive by Gel card were negative by all manual methods. These false positive cases were attributed to reasons such as increased ESR, macrocytosis and marked leucocytosis. Nine cases were negative by Gel card but were positive with the Monospecific AHG. The sensitivity of DCT done by the Gel card technique was 83.01% and the specificity was 60.46%. Use of Gel card technique to perform and interpret DCT is easier than manual tube methods, but positivity by Gel card needs to be correlated with clinical presentation of the patient and other laboratory findings. Monospecific antisera can be used to confirm cases that are positive by the Gel card systems.

Isotype-specific detection of ABO blood group antibodies using a novel flow cytometric method

Several methods to detect anti-A/B antibodies based on haemagglutination and haemolysis have been described. These methods measure predominantly anti-A/B immunoglobulin (Ig)M, whereas anti-A/B IgG and IgG subclasses are less well examined. We established a flow cytometry method (ABO-fluorescence-activated cell sorting; ABO-FACS) to quantify binding of anti-A/B IgM, IgG and IgG subclasses to human A or B red blood cells. Anti-A/B IgM were present in the majority of 120 blood donors, as expected from blood group typing. The sensitivity and specificity of anti-A/B IgM to predict the blood group was 93% and 96% respectively. Anti-A/B IgG was found in 34/38 blood group O samples (89%). Anti-B IgG in blood group A or anti-A IgG in blood group B was present in 4/28 (14%) and 1/28 (4%) samples, respectively, and absent in 26 AB sera. IgG2 was the predominant IgG subclass. The correlation of anti-A/B IgM and IgG in the ABO-FACS with haemagglutination titres was 0.870 and 0.783, respectively (n = 240; P < 0.001) whereas the comparison of ABO-FACS with ABO-enzyme-linked immunosorbent assay was less significant. In conclusion, ABO-FACS is a valid method to quantify anti-A/B IgM, IgG and IgG subclasses. It opens the possibility of isotype-specific monitoring of anti-A/B antibodies levels after ABO-incompatible solid organ and stem cell transplantation.

Gel test assay for IgG subclass detection by GM typing: application to hemolytic disease of the newborn

The gel test assay was evaluated for IgG subclass detection by GM typing of antibodies and compared to the classical inhibition agglutination method on slides or microtiter plates. We used a panel of 5 murine monoclonal antibodies directed against G1M(1), G1M(3), G1M(17), G2M(23), and G3M(21) and 1 human polyclonal anti-G3M(5) antibody. Eleven polyclonal antisera (of immunized women) directed against red blood cells were tested for the GM allotypes carried by their alloantibodies. We controlled the specificity of the gel test reaction using a panel of anti-RH(D) monoclonal antibodies. All reagents exhibited a good reactivity and specificity. They can be used for routine typing. The gel test assay for IgG subclass detection is a specific, simple, and low-cost technique for the detection and management of severe forms of diseases in alloimmunized pregnancies.

[Application of the gel test using and anti-IgA antiglobulin for the immunologic diagnosis of autoimmune hemolytic anemia with a negative direct Coombs test]

Autoimmune hemolytic anemias (AIHA) are characterized by hyperhemolysis associated with the presence of the immunoglobulins IgG, IgM or IgA on the red cell membrane. These immunoglobulins react as auto-antibodies against the red cell auto-antigens of the patient. The diagnosis is supported by clinical and biological signs of hemolysis, and by the identification of the auto-antibodies using the direct antiglobulin test (DAT). Here we report 14 cases of patients who showed the clinical and biological profile of AIHA, but who gave a negative DAT. We therefore tried to determine the presence of IgA on the red cell membrane with a method more sensitive than the DAT: the gel test using anti-IgA. With such a gel test, we demonstrated that there were IgA auto-antibodies on the red cell membrane in the 14 cases, therefore confirming the diagnosis of AIHA. We discuss the interest of performing a gel test with anti-IgA in each case where AIHA is suspected, but in which a negative DAT has been observed.