Development and validation of a -globin-specific ELISA for carrier screening of the (--SEA) thalassaemia deletion

Quantification of human embryonic ζ-globin chains in Southeast Asian deletion (--SEA) carriers

AIMS

Reactivation of embryonic ζ-globin is a promising strategy for genetic treatment of α-thalassaemia. However, quantification of ζ-globin as a quantitative trait in α-thalassaemia carriers and patients remains incompletely understood. In this study, we aimed to set up a reliable approach for the quantification of ζ-globin in α-thalassaemia carriers, followed by a population study to investigate its expression patterns.

METHODS

ζ-globin was purified as monomers from cord blood haemolysate of a Hb Bart's fetus, followed by absolute protein quantification, which was then tested by in-house ELISA system and introduced as protein standard. It was then used for large-scale quantification in peripheral blood samples from 6179 individuals. Finally, liquid chromatography-tandem mass spectrometry (LC-MS/MS) introduced as an independent validating approach by measuring ζ-globin expression in a second cohort of 141-SEA/αα carriers.

RESULTS

The ELISA system was proved sensitive in distinguishing individuals with varied extent of ζ-globin. Large scale quantitative study of this --SEA/αα carrier cohort indicated the high diversity of ζ-globin expression ranging from 0.00155 g/L to 1.48778 g/L. Significant positive correlation between ELISA and LC-MS/MS (R=0.400, p<0.001) was observed and it is more sensitive in distinguishing the samples with extreme expression of ζ-globin (R=0.650, p<0.001).

CONCLUSION

Our study has reported reliable approaches for the quantification of ζ-globin and presented the expression patterns of ζ-globin among the --SEA/αα carrier population, which might lay a foundation on subsequent genotype-phenotype studies on mechanisms of delayed haemoglobin switch in α-thalassaemia.

Immunostick Test for Detecting ζ-Globin Chains and Screening of the Southeast Asian α-Thalassemia 1 Deletion

Background

Couples who carry α-thalassemia-1 deletion are at 25% risk of having a fetus with hemoglobin Bart’s hydrops fetalis. Southeast Asian deletion (−-(SEA)) is the most common type of α-thalassemia 1 among Southeast Asian populations. Thus, identification of the (−-(SEA)) α-thalassemia 1 carrier is necessary for controlling severe α-thalassemia in Southeast Asian countries.

Results

Using our generated anti ζ-globin chain monoclonal antibodies (mAbs) clones PL2 and PL3, a simple immunostick test for detecting ζ-globin chain presence in whole blood lysates was developed. The procedure of the developed immunostick test was as follows. The immunostick paddles were coated with 50 μg/mL of mAb PL2 as capture mAb, or other control antibodies. The coated immunostick was dipped into cocktail containing tested hemolysate at dilution of 1:500, 0.25 μg/mL biotin-labeled mAb PL3 and horseradish peroxidase-conjugated streptavidin at dilution of 1:1000. The immunostick was then dipped in precipitating substrate and the presence of ζ-globin chain in the tested sample was observed by the naked eye. Upon validation of the developed immunostick test with various types of thalassemia and normal subjects, 100% sensitivity and 82% specificity for detection of the (−-(SEA)) α-thalassemia-1 carriers were achieved. The mAb pre-coated immunostick can be stored at room temperature for at least 20 weeks.

Conclusion

In this study, a novel simple immunostick test for the screening of (−-(SEA)) α-thalassemia 1 carriers was presented. The developed immunostick test, within a single test, contains both positive and negative internal procedural controls.

Screening of (-SEA) α-thalassaemia using an immunochromatographic strip assay for the ζ-globin chain in a population with a high prevalence and heterogeneity of haemoglobinopathies

AIMS

The presence of the ζ-globin chain is a good marker of (--^SEA) α⁰-thalassaemia. We evaluated an immunochromatographic (IC) strip assay for ζ-globin in screening for (--^SEA) α⁰-thalassaemia in a population with a high prevalence and heterogeneity of haemoglobinopathies.

METHODS

The study was carried out on 300 screen positive blood samples of Thai individuals. The IC strip assay for the ζ-globin chain was performed on all samples. The results were interpreted with thalassaemia genotyping using standard haemoglobin and DNA analyses.

RESULTS

Several thalassaemia genotypes were noted. Among the 300 subjects investigated, 79 had a positive IC strip assay for ζ-globin and (--^SEA) α⁰-thalassaemia was identified in 40 of them. No (--^SEA) α⁰-thalassaemia was detected in the remaining 39 samples with a positive IC strip test result or in the 221 samples with a negative IC strip test result. Further DNA analysis identified α⁺-thalassaemia in 25 of the 39 (--^SEA) α⁰-thalassaemia negative samples. Using this IC strip assay in combination with a conventional screening protocol for (--^SEA) α⁰-thalassaemia could provide sensitivity and specificity of 100% and 90.4%, respectively.

CONCLUSIONS

IC strip assay for ζ-globin is simple, rapid and does not require sophisticated equipment. Use of this test in addition to the existing screening protocol could detect potential (--^SEA) α⁰-thalassaemia leading to a significant reduction in the workload of DNA analysis. This could be used in areas where haemoglobinopathies are prevalent and heterogeneous but molecular testing is not available.

Compound heterozygosity for KLF1 mutations is associated with microcytic hypochromic anemia and increased fetal hemoglobin

Krüppel-like factor 1 (KLF1) regulates erythroid lineage commitment, globin switching, and the terminal maturation of red blood cells. Variants in human KLF1 have been identified as an important causative factor in a wide spectrum of phenotypes. This study investigated two unrelated male children in China who had refractory anemia associated with poikilocythemia. These were accompanied by an upregulation of biochemical markers of hemolysis, along with abnormal hemoglobin (Hb) level and elevated reticulocyte counts. Next-generation sequencing revealed that the patients were compound heterozygotes for a KLF1 frameshift mutation c.525_526insCGGCGCC (p.(Gly176ArgfsTer179)) and one of two missense variants, c.892 G>C (p.(Ala298Pro)) and c.1012C>T (p.(Pro338Ser)). The subjects had microcytic hypochromic anemia, and their healthy parents had single mutation. The two missense mutations affected a highly conserved codon in the zinc finger DNA-binding domain of KLF1, but the protein stability was unaffected in K-562 cells. A KLF1-targeted promoter-reporter assay showed that the two mutations reduce the expression of the HBB, BCL11A, and CD44 genes involved in erythropoiesis, with consequent dyserythropoiesis and an α/non-α chain imbalance. A systematic analysis was performed of the phenotypes associated with the KLF1 mutations in the two families, and the clinical characteristics and differential diagnoses of the disease are presented. This is the first report of an autosomal recessive anemia presenting with microcytic hypochromia, abnormal Hb profile, and other distinctive erythrocyte phenotypes, and provides insight into the multiple roles of KLF1 during erythropoiesis.

A simple and highly sensitive ELISA for screening of the α-thalassemia-1 Southeast Asian-type deletion

Couples in which both partners carry the α-thalassemia-1 trait have a 25% risk of hemoglobin Bart's hydrops fetalis in each pregnancy. Identification of α-thalassemia-1 trait is, therefore, necessary in order to control this severe form of α-thalassemia. We have generated monoclonal antibodies specific to the ζ-globin chain without cross reaction with other globin chains. A simple and sensitive ELISA was developed by using poly-l-lysine to increase the protein binding to the ELISA plate. The developed poly-l-lysine pre-coated ELISA has a very high sensitivity (100%) and specificity (97%) for detection of carriers of α-thalassemia-1 with Southeast Asian-type deletion.

Routine screening for α-thalassaemia using an immunochromatographic strip assay for haemoglobin Bart's

Objective

To evaluate an immunochromatographic (IC) strip assay for Hb Bart's as a routine screening test for α-thalassaemia in area with a high prevalence of thalassaemia and haemoglobinopathies.

Methods

A total of 300 adult screen positive blood specimens were collected at an ongoing thalassaemia screening programme in northeast Thailand. Routine screening was done using red blood cell indices, osmotic fragility, and dichlorophenolindophenol tests. The IC strip assay for haemoglobin Bart's was performed on all samples. The result was evaluated against thalassaemia genotypes determined using standard haemoglobin and DNA analyses.

Results

Of 300 subjects investigated, Hb and DNA analyses identified 32 with normal genotype. The remaining subjects carried thalassaemia with as many as 16 different genotypes. Hb Bart's was detected in all cases, with several α0-thalassaemia (SEA type) related disorders. Of cases with α+-thalassaemia, 86.1% showed a positive result; 100 out of 103 Hb E carriers, all homozygous Hb E and β-thalassaemia trait were negative. Nine out of 17 cases with β-thalassaemia/Hb E disease, and one case of double heterozygote for Hb Q-Thailand and Hb E returned positive results. The overall sensitivity and specificity of the IC strip assay for detecting α0-thalassaemia were 100% and 73.1%, respectively.

Conclusion

The results showed a high sensitivity for screening for α0-thalassaemia using IC strip assay for Hb Bart's. This simple method, used in combination with conventional screening protocols, should lead to a significant reduction in the number of referral cases for DNA analysis. Cost effectiveness in each population should be taken into consideration.

KLF1 mutations are relatively more common in a thalassemia endemic region and ameliorate the severity of β-thalassemia

Mutations in human Krüppel-like factor 1 (KLF1) have recently been reported to be responsible for increased fetal hemoglobin (HbF) and hemoglobin A2 (HbA2). Because increased HbF and HbA2 levels are important features of β-thalassemia, we examined whether there is any relationship between KLF1 mutation and β-thalassemia in China. To do this, we first studied the incidence of KLF1 mutations in 2 Chinese populations: 3839 individuals from a thalassemia endemic region in south China and 1190 individuals from a non-thalassemia endemic region in north China. Interestingly, we found that the prevalence of KLF1 mutations is significantly higher in the thalassemia endemic region than that in non-thalassemia endemic region (1.25% vs 0.08%). Furthermore, we identified 7 functional variants including 4 previously reported (p.Gly176AlafsX179, p.Ala298Pro, p.Thr334Arg, and c.913+1G>A) and 3 novel variants (p.His299Asp, p.Cys341Tyr, and p.Glu5Lys) in southern China. The 2 most common mutations, p.Gly176AlafsX179 and p.His299Asp, accounted for 90.6% of the total. We found that zinc-finger mutations in KLF1 were selectively represented in 12 β-thalassemia intermedia patients and resulted in significantly different transfusion-free survival curves. Our findings suggest that KLF1 mutations occur selectively in the presence of β-thalassemia to increase the production of HbF, which in turn ameliorates the clinical severity of β-thalassemia.

Characteristics of anaphylaxis-inducing IgG immune complexes triggering murine passive systemic anaphylaxis

BACKGROUND

With the broad and increasing application of therapeutic monoclonal antibodies (mAbs) in clinical settings, IgG-induced allergic reactions, including passive systemic anaphylaxis (PSA), have attracted significant attention. However, it is not clear which types of IgG mAb-antigen complexes or IgG aggregates formed by antigen binding can trigger PSA, as not all immune complexes (ICs) are capable of triggering PSA. Here, we characterise mAb-antigen complexes capable of inducing murine PSA to evaluate and predict which ICs are able to induce PSA.

METHODS

Thirty-six combinatory reactions with eight antigens and 27 corresponding mAbs were used to trigger PSA, which was defined by rectal temperature. Sandwich ELISA, passive cutaneous anaphylaxis (PCA) induction and flow cytometry analysis of CD16/32 (FcγRIII/II) expression were used to characterise the ICs. The dynamic concentrations of antigen in the peripheral blood were measured by ELISA.

RESULTS

Only 14 of the 36 ICs could trigger PSA and thus be termed anaphylaxis-inducing immune complexes (Ai-ICs). The Ai-ICs could be characterised by constructing sandwich ELISA, inducing PCA and down-regulating CD16/32 (FcγRIII/II) expression on blood neutrophils in vitro and in vivo. Additionally, the occurrence and severity of PSA was found to be associated with the instantaneous concentration of antigen in the peripheral blood in the presence of antibody.

CONCLUSIONS

Only Ai-ICs, not all ICs, could trigger IgG-mediated PSA, which could be characterised by the above simple methods. The occurrence and severity of PSA was associated with the instantaneous concentration of antigen in the peripheral blood in the presence of antibody.

Development of a fluorescence immunochromatographic assay for the detection of zeta globin in the blood of (--(SEA)) α-thalassemia carriers

Southeast Asian deletion (--(SEA)) α-thalassemia is an inherited monogenic disorder of human hemoglobin, and embryonic globin ζ (hemoglobin ζ, zeta globin chain or Hb zeta chain) has been shown to be a marker that can be used for the identification of carriers of the (--(SEA)) α-thalassemia deletion. In this work, a fluorescence immunochromatographic assay (FL-ICA) was established to detect the zeta globin chain in the hemolysates of carriers of the (--(SEA)) α-thalassemia deletion. This assay can be completed within 10min using a simple UV detector and does not suffer from interference from the red background color of the hemolysate. A total of 314 blood samples were tested by FL-ICA and ELISA. The results of these assays were confirmed by PCR, the standard technique for genetic disease testing. The sensitivity and specificity of this novel FL-ICA were 100% and 98.0%, respectively; the corresponding values for the ELISA performed simultaneously were 100% and 99.2%, respectively. In conclusion, a new FL-ICA-a simple, fast, convenient, low-cost method-was developed that may be useful in both high-throughput screening and individual detection of the (--(SEA)) α-thalassemia deletion in carriers. Additionally, this qualitative FL-ICA may enlighten the development of a new systems for analysis of other target molecules using whole-blood samples.