Towards standardizing basophil identification by flow cytometry

Background

Basophils normally make up <2% of the white blood cells (WBC). There is no clear consensus for basophil identification by flow cytometry. The increased demand for basophil activation test (BAT) to identifying and monitoring allergic patients highlights the need for a standardized approach to identify basophils.

Methods

Using flow cytometry we analyzed whole blood stained with antibodies against: IgE, CD123, CD193, CD203c, CD3, HLADR, FcɛRI, CRTH2 and CD45. We examined unstimulated blood as well as blood stimulated with Anti-IgE and fMLP. Finally, we compared the results to a complete blood count (CBC) from an FDA approved hematological analyzer.

Results

Basophil identification relying on just one surface marker performed worse than approaches utilizing two identification markers. The percentage of basophils from WBC determined by flow cytometry results had a good correlation with the CBC results even though the CBC results were generally higher. Stimulating whole blood with the basophil activators did not interfere with the basophil identification markers.

Conclusion

In flow cytometry assays, two surface markers should be used for identifying basophils and if a very pure basophil fraction is desired a third marker can be considered. In our hands the approaches that included CD123 in combination with either CD193, HLADR^negative or FcɛRI performed the best.

Increased expressions of CD123, CD63, CD203c, and Fc epsilon receptor I on blood leukocytes of allergic asthma

Background: Altered basophil identification markers have been discovered to associate with allergic asthma (AA) in recent years. However, little is known about the expression of basophil markers in blood granulocytes.

Aim: To parallel test blood basophils in peripheral blood mononuclear cell (PBMC) and granulocyte populations of patients with AA and AA combined with allergic rhinitis (ARA)

Methods: The expressions of surface molecules were determined via flow cytometry. CD123 expressing cells in blood were isolated using a cell sorting technique, and mouse AA models were employed for in vivo study.

Results: The numbers of CD123⁺HLA-DR⁻ cells in the granulocytes of AA and ARA patients markedly increased. However, only 49.7% of CD123⁺HLA-DR⁻ cells in granulocytes and 99.0% of CD123⁺HLA-DR⁻ cells in PBMCs were basophils. Almost all CD123⁺HLA-DR⁻ cells expressed CD63 regardless in granulocytes or PBMC. The numbers of CD63, Fc epsilon receptor I (FcεRI), and CD203c expressing cells markedly enhanced in CD123⁺HLA-DR⁻ granulocytes of AA and ARA patients. Mean fluorescence intensity (MFI) of CD63 and CD203c expressions on CD123⁺HLA-DR⁻ PBMC and granulocytes of AA and ARA patients dramatically elevated. House dust mite extract (HDME) and Artemisia sieversiana wild allergen extract (ASWE) enhanced the numbers of CD63⁺CD123⁺HLA-DR⁻ granulocytes and PBMC and the MFI of CD203c expression on CD123⁺HLA-DR⁻ granulocyte of AA and ARA patients. Histamine, tryptase, and PGD2 enhanced proportions of CD123⁺ KU812 cells. ASWE- and HDME-induced AA mice showed upregulated CD63 expression on basophils. In conclusion, upregulated expressions of CD123, CD203c, CD63, and FcεRIα in PBMC and granulocytes of patients with AA and ARA suggest that CD123⁺HLA-DR⁻ cells may contribute to the development of AA and ARA.

Innovative robust basophil activation test using a novel gating strategy reliably diagnosing allergy with full automation

BACKGROUND

Allergy is one of the most common chronic diseases in Europe. Therefore, an increased need for specific and sensitive diagnostic tests that truly detect allergy exists. This study aimed at establishing a highly specific high-throughput and automated basophil activation test (BAT) that proves the existence of an allergy with utmost probability.

METHODS

BAT from 1104 samples was analyzed; a novel gating strategy with three antibodies (FcεRIα, CD203c, CD63) was established and compared with our published protocol (12 antibodies). Based on the novel gating strategy, storage conditions, automated measurement, and analyses using R (1376 samples out of 1389) were optimized to set up a high-throughput BAT.

RESULTS

No differences in sensitivity and specificity were found between the novel three antibody (FcεRIα, CD203c, CD63) and the 12 antibody gating strategy or between automated and manually analyzed samples (saving up to 90% of labor time). The time frame for basophil activation measurement after blood donation has been extended considerably (whole blood storage ≤7 days (RT) and 17 days (4°C) prior to BAT preparation and measurement). Respective storage conditions were optimized for samples after stimulation, staining, and preparation (≤7 days (RT) and 28 days (4°C)). These achievements were confirmed by a nationwide ring trial showing robustness and applicability of our BAT on a variety of flow cytometers.

CONCLUSION

Our considerable optimizations overcame the hurdles that until now prevented the BAT from being used as high-throughput allergy diagnostic test in routine laboratories and shall allow for collaborative studies between clinics and research centers.

Upregulated Expression of Toll-Like Receptor 7 in Peripheral Blood Basophils of Patients With Allergic Rhinitis

Background

Recently, it has been reported that Toll-like receptor 7 (TLR7) agonists can improve allergic rhinitis (AR) symptoms by up-regulation of Th1 cytokine release and suppression of Th2 cell functions. However, little is known of the expression of TLR7 in basophils of AR.

Objective

To explore the expression of TLR7 in basophils of AR, and influence of allergens on TLR7 expression.

Methods

The expression levels of TLR7 in basophils of patients with AR were determined by flow cytometry, and the influence of allergens on TLR7 expression was examined by real time (q) PCR.

Results

The percentages of TLR7+CCR3+ cells ( P < 0.001 and P = 0.011), TLR7+CD123+HLA-DR− cells ( P = 0 .016 and P = 0.042) and TLR7+CCR3+CD123+HLA-DR− cells ( P = 0.046 and P = 0.035) in blood granulocyte and mononucleated cell populations of the patients with AR were increased, respectively compared with HC subjects. TLR7 MFI on CCR3+ cells ( P = 0.050 and P = 0.043), CD123+HLA-DR− cells ( P < 0.001 and P = 0.002) and CCR3+CD123+HLA-DR− cells ( P < 0.001 and P = 0.003) were enhanced compared with HC subjects. Allergens Der p1 and OVA provoked upregulation of TLR7 expression at both protein and mRNA levels and IL-13 production in KU812 cells. House Dust Mite extract (HDME), Artemisia sieversiana wild allergen extract (ASWE), IL-31, IL-33, IL-37, and TSLP provoked elevation of IL-6 release from KU812 cells following 2 h incubation period.

Conclusions

The percentage of TLR7+ basophils and TLR7 expression intensity in a single basophil are both increased in the blood of patients with AR, indicating that basophils likely contribute to the pathogenesis of AR via TLR7.

Basophil activation test in allergy diagnostics

The prevalence of allergic diseases in Poland and in the world continues to rise in recent years. The most commonly used methods for diagnosing IgE – dependent allergies are skin prick testing (SPT) and assessment of specific IgE (sIgE) directed against specific allergens. However, both methods have some disadvantages and the obtained results may be inconsistent. In particular, routine diagnostic tests are not always effective for some drugs and foods. Consequently, additional laboratory tools should be used. Basophil activation test (BAT) based on flow cytometry is a promising diagnostic method. The present paper demonstrates the usefulness and effectiveness of BAT protocols in allergy diagnosis in scientific research. In comparison to routinely used diagnostic methods, BAT is an expensive and complicated laboratory tool. However, it offers the possibility to efficiently and effectively recognize allergies. Introducing BAT into routine diagnostics in allergology is problematic because this method has not yet been standardized and validated. Therefore, there is a justified need to continue research in this field. If standardized and validated, BAT may offer a reasonable improvement in allergy diagnostics in the future.

Upregulation of the expression of Toll-like receptor 9 in basophils in patients with allergic rhinitis: An enhanced expression by allergens

It was reported that the expression of Toll-like receptor (TLR) 9 may be related to Th2-type allergic inflammation including allergic rhinitis (AR). However, little is known about the expression of TLR9 in the basophils in AR. In the present study, the expression of TLR9 was examined by flow cytometry analysis, and the expression of TLR9 mRNA in KU812 was determined by quantitative real-time PCR. The results showed that the percentage of TLR9⁺ CCR3⁺ cells in blood granulocytes increased by 46% in patients with AR, but not in peripheral blood mononuclear cells (PBMCs). Allergens namely Dermatophagoide allergen extract (DAE) and Platanus pollen allergen extract (PPAE) upregulated the expression of TLR9 in CCR3⁺ granulocytes by 76% and 84%, respectively. DAE and PPAE also enhanced the proportions of TLR9⁺ CD123⁺ HLA-DR^- cells and TLR9⁺ CCR3⁺ CD123⁺ HLA-DR^- cells in granulocytes and PBMCs of patients with AR. In order to investigate the actions of allergens on basophils, KU812 cells were used. It was observed that all KU812 cells expressed TLR9, and the expression intensity of TLR9 in a single KU812 cell was elevated by CpG. IL-37, IL-31, IL-33, Artemisia sieversiana wild allergen extract (ASWAE), DAE, OVA and Der p 1 induced an increase in the expression of TLR9 mRNA and IL-6 production in KU812 cells. It was shown that the percentage of TLR9-expressing basophils increased in the blood of ovalbumin (OVA)-sensitized mice. In conclusion, an increased expression of TLR9 and the production of IL-6 in basophils implicate that the contribution of basophils to AR is likely via TLR9.

Single-cell transcriptomic landscape of nucleated cells in umbilical cord blood

BACKGROUND

For both pediatric and adult patients, umbilical cord blood (UCB) transplant is a therapeutic option for a variety of hematologic diseases, such as blood cancers, myeloproliferative disorders, genetic diseases, and metabolic disorders. However, the level of cellular heterogeneity and diversity of nucleated cells in UCB has not yet been assessed in an unbiased and systemic fashion. In the present study, nucleated cells from UCB were subjected to single-cell RNA sequencing to simultaneously profile the gene expression signatures of thousands of cells, generating a rich resource for further functional studies. Here, we report the transcriptomes of 17,637 UCB cells, covering 12 major cell types, many of which can be further divided into distinct subpopulations.

RESULTS

Pseudotemporal ordering of nucleated red blood cells identifies wave-like activation and suppression of transcription regulators, leading to a polarized cellular state, which may reflect nucleated red blood cell maturation. Progenitor cells in UCB also comprise 2 subpopulations with activation of divergent transcription programs, leading to specific cell fate commitment. Detailed profiling of cytotoxic cell populations unveiled granzymes B and K signatures in natural killer and natural killer T-cell types in UCB.

CONCLUSIONS

Taken together, our data form a comprehensive single-cell transcriptomic landscape that reveals previously unrecognized cell types, pathways, and mechanisms of gene expression regulation. These data may contribute to the efficacy and outcome of UCB transplant, broadening the scope of research and clinical innovations.

In Vitro Diagnosis of Immediate Drug Hypersensitivity Anno 2017: Potentials and Limitations

Background

For most physicians, quantification of drug-specific immunoglobulin E (drug-sIgE) antibodies constitutes the primary in vitro measure to document immediate drug hypersensitivity reactions (IDHR). Unfortunately, this is often insufficient to correctly identify patients with IgE-mediated IDHR and impossible for non-IgE-mediated IDHR that result from alternative routes of basophil and mast cell activation. In these difficult cases, diagnosis might benefit from cellular tests such as basophil activation tests (BAT).

Aim

The aim was to review the potential and limitations of quantification of sIgE and BAT in diagnosing IDHR. The utility of quantification of serum tryptase is discussed.

Methods

A literature search was conducted using the key words allergy, basophil activation, CD63, CD203c, diagnosis, drugs, hypersensitivity, flow cytometry, specific IgE antibodies; this was complemented by the authors’ own experience.

Results

The drugs that have been most studied with both techniques are β-lactam antibiotics and curarizing neuromuscular blocking agents (NMBA). For sIgE morphine, data are available on the value of this test as a biomarker for sensitization to substituted ammonium structures that constitute the major epitope of NMBA, especially rocuronium and suxamethonium. For the BAT, there are also data on non-steroidal anti-inflammatory drugs (NSAIDs) and iodinated radiocontrast media. For β-lactam antibiotics, sensitivity and specificity of sIgE varies between 0 and 85% and 52 and 100%, respectively. For NMBA, sensitivity and specificity varies between 38.5 and 92% and 85.7 and 100%, respectively. Specific IgE to morphine should not be used in isolation to diagnose IDHR to NMBA nor opiates. For the BAT, sensitivity generally varies between 50 and 60%, whereas specificity attains 80%, except for quinolones and NSAIDs.

Conclusions

Although drug-sIgE assays and BAT can provide useful information in the diagnosis of IDHR, their predictive value is not absolute. Large-scale collaborative studies are mandatory to harmonize and optimize test protocols and to establish drug-specific decision thresholds.

The CLEC12A receptor marks human basophils: Potential implications for minimal residual disease detection in acute myeloid leukemia

BACKGROUND

The transmembrane receptor C-type lectin domain family 12, member A (CLEC12A) is known to be highly expressed on monocytes and neutrophils and is a reliable leukemia associated marker in acute myeloid leukemia. Consequently, detailed knowledge of the various normal cell types expressing this receptor is essential. We have observed CLEC12A to be expressed on CD45lowSSClowCD14-CD123+ basophils in peripheral blood (PB) and in this study, we aimed at verifying this observation and further delineate the CD45lowSSClowCD14-CD123 + CLEC12A+ subpopulation.

METHODS

We analyzed PB from 20 diagnostic chronic myeloid leukemia (CML) samples and eight healthy donors in a six-color multicolor flowcytometry (FCM) based assay. Furthermore, we performed fluorescence activated cell sorting on one CML sample to morphologically confirm the CD45lowSSClowCD14-CD123 + CLEC12A+ subset to be highly enriched for basophils. Finally, to further delineate the CD45lowSSClowCD14-CD123 + CLEC12A+ subpopulation in normal PB, we examined three healthy donors in a 10-color FCM assay enabling further separation of the cell subset into basophils and dendritic cells.

RESULTS

The CLEC12A receptor is expressed on basophils.

CONCLUSIONS

Identification and enumeration of basophils is of high relevance in diagnostic hematology and immunology. We here show that CLEC12A in a simple FCM assay consistently marks basophils. Importantly, as basophils are characterized by a CD45lowSSClow profile similar to the "blast-gate" used for the evaluation of hematological disorders, awareness of minor normal CLEC12A+ subpopulations is crucial when using CLEC12A as a minimal residual disease marker in myeloid malignancies. © 2017 International Clinical Cytometry Society.

Peanut oleosins associated with severe peanut allergy-importance of lipophilic allergens for comprehensive allergy diagnostics

BACKGROUND

Peanut allergy is one of the most common and most severe food allergies in Western countries and its accurate diagnosis to prevent potential life-threatening allergic reactions is crucial. However, aqueous extracts used for routine diagnostic measurements are devoid of lipophilic allergens such as oleosins. We have recently succeeded in the isolation and purification of these unique proteins, and the present study evaluates their allergenic potential and clinical relevance.

OBJECTIVE

We sought to assess allergenicity and sensitization prevalence of oleosins obtained from both raw and in-shell roasted peanuts. In addition, we tested the utilization of natural and recombinant oleosins for allergy diagnostic purposes.

METHODS

Oleosin sensitization, prevalence, and impact of thermal processing were analyzed by immunoblot with sera from 52 peanut-allergic individuals displaying different clinical phenotypes. The application of natural and recombinant oleosins for allergy diagnostics was investigated by basophil activation test (BAT). IgE-binding epitopes were identified by oligopeptide microarray.

RESULTS

Sensitization to oleosins was observed exclusively in peanut-allergic subjects suffering from severe systemic reactions. IgE-binding capacity of oleosins derived from in-shell roasted peanuts was increased as shown by immunoblot analysis and BAT. Both natural and recombinant molecules can be used to identify oleosin-sensitized patients by BAT. A linear epitope of Ara h 15 was determined that displays high similarity to other seed-derived oleosins.

CONCLUSIONS

Oleosins are clinically relevant peanut allergens and most likely associated with severe allergic symptoms. In-shell roasting increases their allergenicity, which is consistent with the observation that most allergic reactions are in connection with roasted peanuts.

Basophil markers for identification and activation in the indirect basophil activation test by flow cytometry for diagnosis of autoimmune urticaria

Background

The indirect basophil activation test using flow cytometry is a promising tool for autoimmune urticaria diagnosis. We aimed to identify better donor basophils (from atopic vs. non-atopic donors and interleukin-3 primed vs. unprimed basophils) and improve basophil identification and activation markers (eotaxin CC chemokine receptor-3 [CCR3] vs. CD123 and CD63 vs. CD203c).

Methods

Donor basophils were obtained from non-atopic and atopic group O donors. Positive control sera were artificially prepared to simulate autoimmune urticaria patients' sera. Patient sera were obtained from nine children with chronic urticaria. Assay sensitivity was compared among each variation by using positive control sera (n=21), applying cutoff values defined from negative control sera (n=20).

Results

For basophil identification, a combination of CCR3 and CD123 markers revealed a higher correlation with automated complete blood count (r=0.530) compared with that observed using CD123 (r=0.498) or CCR3 alone (r=0.195). Three activation markers on the atopic donor basophils attained 100% assay sensitivity: CD203c on unprimed basophils, CD63+CD203+ or CD63 alone on primed basophils; however, these markers on the non-atopic donor basophils attained lower assay sensitivity.

Conclusions

For basophil identification markers, a combination of CD123 and CCR3 is recommended, while CD123 alone may be used as an alternative. Donor basophils should be obtained from an atopic donor. For basophil activation markers, either CD203c alone on unprimed basophils or CD203c and CD63 on primed basophils are recommended, while CD63 alone on primed basophils may be used as an alternative.

Basophil activation test in oral desensitization to cow's milk allergy

The recent paper by Nucera et al., showed that the basophil activation test (BAT) in flow cytometry is able to monitor an acquired tolerance induced by a desensitization treatment in food allergy. The paper by Nucera et al. reported two standpoints in the CD63 response to food allergy and OAT and their large difference in CD63 response before and after suggests for the optimal performance of a CD123/HLADR/CD63 BAT in oral food allergy immunotherapy.

The expression of CD123 can decrease with basophil activation: implications for the gating strategy of the basophil activation test

Background

Basophil activation test (BAT) reproduces IgE-mediated allergic reactions in vitro and has been used as a diagnostic test. Different markers can be used to identify basophils in whole blood and have implications for the outcome of the test. We aimed to assess changes in the expression of CD123 and HLA-DR following basophil activation and to select the best gating strategy for BAT using these markers.

Methods

BAT was performed in whole blood from 116 children. Peanut extract, anti-IgE, anti-FcεRI or formyl-methionyl-leucyl-phenylalanin (fMLP) was used for stimulation. Surface expression of CD123, HLA-DR, CD63 and CD203c was evaluated by flow cytometry.

Results

In some cases, gating on CD123+/HLA-DR− led to the loss-to-analysis of basophils in conditions where basophils were activated. Adding CD203c as an identification marker restored the cell number. Basophils remained HLA-DR-negative with activation. CD123 expression decreased following stimulation with fMLP (n = 116, p < 0.001), anti-IgE (n = 104, p < 0.001) and peanut (n = 42, p < 0.001). The decrease in the mean fluorescence intensity of CD123 correlated with the up-regulation of basophil activation markers, CD63 (r_s = −0.31, p < 0.001) and CD203c (r_s = −0.35, p < 0.001). BAT to peanut gating basophils on CD203c+/CD123+/HLA-DR− reduced the false-negatives (1 vs. 5 %) and showed a higher diagnostic accuracy compared to using CD123+/HLA-DR− (97 vs. 91 %). CD203c+ appeared as an alternative gating strategy allowing two-colour BAT.

Conclusions

Basophils of a subset of patients down-regulate CD123 with activation. The use of CD203c before gating on CD123+/HLA-DR− cells or in isolation ensures the identification of the entire basophil population and accurate assessment of basophil activation, with important diagnostic implications.

Pimecrolimus Is a Potent Inhibitor of Allergic Reactions to Hymenopteran Venom Extracts and Birch Pollen Allergen In Vitro

Pimecrolimus (Elidel, SDZ ASM 981) is an anti-inflammatory and immunomodulatory 33-epichloro-derivative of macrolactam ascomycin, with low potential for affecting systemic immune responses compared with other calcineurin inhibitors, cyclosporin A and tacrolimus. Despite numerous studies focused on the mechanism of pimecrolimus action on mast cells, only the single report has addressed pimecrolimus effects on other typical FcεRI-expressing cells, the basophils. Patients allergic to birch pollen (n = 20), hymenopteran venoms (n = 23) and 10 non-allergic volunteers were examined. Primary human basophils pre-treated or not with 0.5-50 μMol pimecrolimus were exposed to various concentrations of recombinant Bet v 1a allergen, bee or wasp venom extracts and anti-IgE for 20 min, and then examined for the expression of CD45, CD193, CD203c, CD63 and CD164 using flow cytometry. The externalization of basophil activation markers (CD63 and CD164) was equally inhibited through pimecrolimus in cells activated by recombinant pollen allergen, hymenopteran venom extracts and anti-IgE. Although the individual response rate was subject to strong variation, importantly, pre-treatment with pimecrolimus lowered the number of activated basophils in response to any of the stimuli in the basophils from all patients. The inhibition was concentration-dependent; approximately half of the basophils were inhibited in the presence of 2.5 mMol pimecrolimus. Pimecrolimus is a valuable new tool for the inhibition of hyper-reactive basophils in patients with pollen allergy and a history of anaphylactic reactions to bee or wasp venoms. Further research should address short-term use of pimecrolimus in vivo in a wide spectrum of allergic diseases.

Immunotherapy in allergy and cellular tests: state of art

The basophil activation test (BAT) is an in vitro assay where the activation of basophils upon exposure to various IgE-challenging molecules is measured by flow cytometry. It is a cellular test able to investigate basophil behavior during allergy and allergy immunotherapy. A panoply of critical issues and suggestive advances have rendered this assay a promising yet puzzling tool to endeavor a full comprehension of innate immunity of allergy desensitization and manage allergen or monoclonal anti-IgE therapy. In this review a brief state of art of BAT in immunotherapy is described focusing onto the analytical issue pertaining BAT performance in allergy specific therapy.

Evaluation of CCR3 as a basophil activation marker

OBJECTIVES

Recent reports have provided conflicting evidence on the stability of CCR3 expression on the surface of basophils. Hence we wanted to independently evaluate the diagnostic usefulness of CCR3 as a surrogate marker of basophil activation and function.

METHODS

We examined the correlative relationship between CCR3 expression on the surface of donor basophils and histamine release after donor basophils were treated with agonistic antibodies directed against the high-affinity IgE-Fc receptor and serum samples from 80 individuals displaying symptoms of chronic urticaria (CU).

RESULTS

We observed that CCR3 was significantly downregulated on donor basophils treated with the agonistic antibody and CU-patient serum that demonstrated positive "histamine-releasing activity" (HRA scores >10). However, CCR3 downregulation was also observed on donor basophils incubated with more than 40% of CU-patient serum samples with HRA scores less than or equal to 10.

CONCLUSIONS

Overall our data show that CCR3 demonstrates adequate sensitivity (83%) but weak specificity (59%) in its ability to reliably identify histamine-releasing activated basophils.