Flow cytometric evaluation of human basophils

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.

Oral Immunotherapy and Basophil and Mast Cell Reactivity in Food Allergy

Basophil activation tests (BATs) can closely monitor, in vitro, a patient's propensity to develop type I hypersensitivity reactions. Because of their high specificity and sensitivity, BATs have become promising diagnostic tools, especially in cases with equivocal clinical histories, skin prick test results, and/or levels of specific IgE to allergen extracts. BATs also are useful as tools for monitoring the effects of treatment, since oral immunotherapy (OIT) studies report a diminution in patients' basophil responsiveness over the course of OIT. This review will discuss the BAT findings obtained before, during, and after OIT for food allergy. We will mainly focus on the association of basophil responsiveness, and alterations in basophil surface markers, with clinical outcomes and other clinical features, such as blood levels of specific IgG and IgE antibodies. The detailed analysis of these correlations will ultimately facilitate the use of BATs, along with other blood biomarkers, to differentiate short-term desensitization versus sustained unresponsiveness and to improve treatment protocols. Given the critical anatomic location of mast cells adjacent to the many IgE+ plasma cells found in the gastrointestinal tissues of allergic individuals, we will also discuss the role of gastrointestinal mast cells in manifestations of food allergies.

Identification of Murine Basophils by Flow Cytometry and Histology

Here, we describe how murine basophils can be detected in vivo by flow cytometry and immunofluorescence staining. Basophils constitute a homogeneous population of CD4^-CD19^-CD49b⁺IgE⁺ cells in flow cytometric analysis. When IgE levels are low, one can also use anti-FcεRI or anti-CD200R3 antibodies instead of anti-IgE. For immunofluorescence staining, we use an anti-Mcpt8 antibody since Mcpt8 is a specific marker for murine basophils. We describe how to prepare the tissue to cut cryo-sections and how to perform the staining using a tyramide-based amplification kit.

Polycyclic aromatic hydrocarbons from diesel emissions exert proallergic effects in birch pollen allergic individuals through enhanced mediator release from basophils

BACKGROUND

Diesel exhaust particles (DEPs) act as adjuvants in the immune system and contribute to the increased prevalence and morbidity of asthma and allergic rhinitis. Polycyclic aromatic hydrocarbons (PAHs) are major components of DEPs, which may be involved in the induction and enhancement of proallergic processes. In this study we explored adjuvant effects of DEP-PAHs on activation parameters of human basophils, fostering allergic inflammation through the release of preformed or granule-derived mediators.

METHODS

Heparinized blood samples from birch pollen allergic and control donors were stimulated with Bet v 1, the major allergen of birch pollen grains, alone or together with a mixture of 16 environmental prominent PAHs (EPA-PAH standard). Flow cytometric analysis was performed for quantitative determination of PAH-enhanced basophil activation. To assess direct PAH effects on basophils, enriched cultures from both donor groups were exposed to benzo[a]pyrene (B[a]P) or phenanthrene (Phe), two major DEP-PAHs, with and without allergen. Supernatants were assayed for IL-4 and IL-8 secretion and histamine release by means of ELISA.

RESULTS

At environmental relevant exposure levels EPA-PAH standard synergized with antigen and significantly enhanced basophil activation of all birch pollen allergic individuals up to 95%. Single PAHs significantly drove IL-8 secretion from sensitized basophils of all patients tested, and there was no further enhancement by addition of rBet v 1. B[a]P and Phe also significantly induced IL-4 secretion, a key factor for Th2 development, from purified sensitized basophils in the absence of antigen suggesting an adjuvant role of DEP-PAHs in allergic sensitization. None of the basophil samples from healthy controls showed any PAH effect on mediator release.

CONCLUSION

DEP-PAHs exert proallergic effects on sensitized basophils in an allergen independent fashion, suggesting a potential role of these pollutants for the allergic breakthrough in atopic individuals, who have not developed an allergic disease yet.

Differential response of human basophil activation markers: a multi-parameter flow cytometry approach

BACKGROUND

Basophils are circulating cells involved in hypersensitivity reactions and allergy but many aspects of their activation, including the sensitivity to external triggering factors and the molecular aspects of cell responses, are still to be focused. In this context, polychromatic flow cytometry (PFC) is a proper tool to investigate basophil function, as it allows to distinguish the expression of several membrane markers upon activation in multiple experimental conditions.

METHODS

Cell suspensions were prepared from leukocyte buffy coat of K2-EDTA anticoagulated blood specimens; about 1500-2500 cellular events for each tested sample, gated in the lymphocyte CD45dim area and then electronically purified as HLADRnon expressing/CD123bright, were identified as basophilic cells. Basophil activation with fMLP, anti-IgE and calcium ionophore A23187 was evaluated by studying up-regulation of the indicated membrane markers with a two-laser six-color PFC protocol.

RESULTS

Following stimulation, CD63, CD13, CD45 and the ectoenzyme CD203c up-regulated their membrane expression, while CD69 did not; CD63 expression occurred immediately (within 60 sec) but only in a minority of basophils, even at optimal agonist doses (in 33% and 14% of basophils, following fMLP and anti-IgE stimulation respectively). CD203c up-regulation occurred in the whole basophil population, even in CD63non expressing cells. Dose-dependence curves revealed CD203c as a more sensitive marker than CD63, in response to fMLP but not in response to anti-IgE and to calcium ionophore.

CONCLUSION

Use of polychromatic flow cytometry allowed efficient basophil electronic purification and identification of different behaviors of the major activation markers. The simultaneous use of two markers of activation and careful choice of activator are essential steps for reliable assessment of human basophil functions.

Allergen-induced basophil CD203c expression as a biomarker for rush immunotherapy in patients with Japanese cedar pollinosis

BACKGROUND

Rush immunotherapy (RIT) can confer rapid clinical benefit on patients with allergic rhinitis or asthma. However, biomarkers representing mechanisms for the efficacy of RIT are still to be established. CD203c is a basophil activation marker known to be upregulated by cross-linking of the FcepsilonRIalpha receptor and may serve as a useful marker.

OBJECTIVE

We sought to investigate the changes in allergen-induced CD203c expression in patients with Japanese cedar pollen (JCP) pollinosis who received RIT.

METHODS

Nine patients treated with RIT were enrolled in the study. Whole blood was incubated with various concentrations of JCP extract. CD203c expression on basophils was quantitated by means of flow cytometry. JCP-specific IgG4 levels in sera were measured with ELISA. Basophil histamine release, CAP-RAST to JCP (JCP-IgE) and total IgE were also examined. The biomarkers listed above were evaluated before and sequentially after RIT. Symptom and quality of life scores were obtained during pre- and posttreatment pollen seasons.

RESULTS

All patients showed significant improvement in symptom and quality of life scores after RIT. Serum JCP-specific IgG4 titers were significantly elevated at 1 month and remained at high levels 12 months after the treatment. Stimulation with JCP extract induced enhancement of basophil CD203c expression in a concentration-dependent manner except for 2 subjects in whom no increase in CD203c by an anti-IgE antibody was observed (nonresponders). Significant reductions in the responses were observed in 4 subjects after RIT (reduction in CD203c expression, RCE) whereas no changes were seen in 3 subjects (non-RCE). RCE subjects were older than non-RCE counterparts, with mean ages of 20 and 12 years, respectively. No significant changes in JCP-specific IgE and total IgE levels were seen before and after RIT.

CONCLUSION

Allergen-induced CD203c expression in basophils may represent, at least in part, the cellular mechanism for the therapeutic responses to RIT for JCP pollinosis. However, further larger-scale studies to confirm the utility of the test are necessary.

Environmental polycyclic aromatic hydrocarbons (PAHs) enhance allergic inflammation by acting on human basophils

Diesel exhaust particles (DEPs) have been implicated in the worldwide increased incidence of allergic airway diseases over the past century. There is growing evidence that DEP-associated polycyclic aromatic hydrocarbons (PAHs) participate in the development and maintenance of immunoglobulin (Ig) E-mediated allergic diseases. To address this issue we investigated the impact of U.S. Environmental Protection Agency (EPA) priority PAHs as well as of PAH-containing airborne extracts on antigen-induced CD63 upregulation and mediator release from human basophils. Whole blood samples from birch pollen allergic and control subjects were incubated in the presence of organic extracts of urban aerosol (AERex) or EPA-PAH standard with or without rBet v 1. Basophils were analyzed for CD63 expression as a measure of basophil activation by using multiparameter flow cytometry. In addition, purified basophils from birch pollen allergic donors were incubated for 2 h in the presence of 1 muM benzo[a]pyrene (BaP) or phenanthrene (Phe) and then stimulated with rBet v 1 for 45 min. Supernatants were assayed for histamine, interleukin (IL)-4, and IL-8 by means of enzyme-linked immunosorbent assay (ELISA). Basophils exposed in vitro simultaneously to AERex or EPA-PAH standard and rBet v 1 expressed CD63 significantly more than with antigen alone. PAHs synergized with rBet v 1 dose dependently, but did not activate basophils from nonallergic donors. BaP and Phe significantly enhanced cytokine secretion (IL-4, IL-8) and histamine release from purified basophils without antigen added, and secretion was not further enhanced by rBet v 1 stimulation. In conclusion, PAHs from roadside emissions can directly activate sensitized basophils to cytokine secretion and drive proallergic processes through enhanced Fcepsilon RI-coupled mediator release from human basophils.

Myocardial Functional and Textural Findings of the Right and Left Ventricles and Their Association with Cellular Adhesion Molecules in Behçet's Disease

AIM

This study was designed to assess whether ultrasonic reflectivity, evaluated by integrated backscatter analysis was associated with the severity of inflammation and diastolic dysfunction of the left (LV) and right ventricles (RV) in Behçet's disease (BD).

METHODS

The study consisted of 20 patients with BD and 18 healthy controls. The expression of CD11b and CD63 on the surface of granulocytes and monocytes were measured by flow cytometry. RV and LV diastolic functions were assessed by tricuspid and mitral annular tissue Doppler recordings, respectively. Backscatter cyclic variation (CV) and maximal intensity (IB) were measured in RV lateral wall, interventricular septum, and posterior LV wall from parasternal long-axis view, apex from apical four-chamber view, anterior, inferior, and lateral LV walls from parasternal short axis view.

RESULTS

The mean fluorescence intensity (MFI) of CD11b on granulocytes and CD63 on monocytes in BD patients was higher than those of controls. Patients with BD had smaller mitral and tricuspid annular early diastolic wave velocities and early/late diastolic wave velocity ratios (E/A) than controls. MFI of CD11b and CD63 was inversely correlated with tricuspid and mitral annular E/A in BD patients. CV of RV and global CV of LV were found to be diminished in BD patients than controls. CV of RV and global CV of LV showed a direct correlation with tricuspid and mitral annular E/A ratio, respectively.

CONCLUSION

There is an association between the levels of cellular adhesion molecules, deterioration of diastolic function, and altered myocardial ultrasonic reflectivity in BD.

Flow Cytometric Analysis of Normal and Neoplastic Mast Cells: Role in Diagnosis and Follow-Up of Mast Cell Disease

Human mast cells (MCs) are directly derived from human pluripotent CD34+ stem and progenitor hematopoietic cells with stem cell factor being a critical growth factor supporting human MC proliferation, differentiation, and survival. Because of the advantages that flow cytometry offers (it allows rapid, objective, and sensitive multiparameter analysis of high numbers of cells from a sample, with information being provided on the basis of a single cell), it has become the method of choice in the past decade for immunophenotypic identification, enumeration, and characterization of human MCs in bone marrow and other tissue specimens.

Immunology and homeopathy. 2. Cells of the immune system and inflammation

Here we describe the results of some experimental laboratory studies aimed at verifying the efficacy of high dilutions of substances and of homeopathic medicines in models of inflammation and immunity. Studies carried out on basophils, lymphocytes, granulocytes and fibroblasts are reviewed. This approach may help to test under controlled conditions the main principles of homeopathy such as 'similarity' of drug action at the cellular level and the effects of dilution/dynamization on the drug activity. The current situation is that few and rather small groups are working on laboratory models for homeopathy. Regarding the interpretation of data in view of the simile principle, we observe that there are different levels of similarity and that the laboratory data give support to this principle, but have not yet yielded the ultimate answer to the action mechanism of homeopathy. Evidence of the biological activity in vitro of highly diluted-dynamized solutions is slowly accumulating, with some conflicting reports. It is our hope that this review of literature unknown to most people will give an original and useful insight into the 'state-of-the-art' of homeopathy, without final conclusions 'for' or 'against' this modality. This kind of uncertainty may be difficult to accept, but is conceivably the most open-minded position now.

The basophil activation test by flow cytometry: recent developments in clinical studies, standardization and emerging perspectives

The diagnosis of immediate allergy is mainly based upon an evocative clinical history, positive skin tests (gold standard) and, if available, detection of specific IgE. In some complicated cases, functional in vitro tests are necessary. The general concept of those tests is to mimic in vitro the contact between allergens and circulating basophils. The first approach to basophil functional responses was the histamine release test but this has remained controversial due to insufficient sensitivity and specificity. During recent years an increasing number of studies have demonstrated that flow cytometry is a reliable tool for monitoring basophil activation upon allergen challenge by detecting surface expression of degranulation/activation markers (CD63 or CD203c). This article reviews the recent improvements to the basophil activation test made possible by flow cytometry, focusing on the use of anti-CRTH2/DP2 antibodies for basophil recognition. On the basis of a new triple staining protocol, the basophil activation test has become a standardized tool for in vitro diagnosis of immediate allergy. It is also suitable for pharmacological studies on non-purified human basophils. Multicenter studies are now required for its clinical assessment in large patient populations and to define the cut-off values for clinical decision-making.

Identification of CD13, CD107a, and CD164 as novel basophil-activation markers and dissection of two response patterns in time kinetics of IgE-dependent upregulation

Using two-colour flow cytometry >200 antibodies submitted to the 8th International Workshop of Human Leukocyte Differentiation Antigens (HLDA8) have been analyzed for their reactivity with resting and activated CD203c+ basophils. Four antibodies either non-reactive or weakly reactive with resting basophils exhibited an increased reactivity with basophils activated by anti-IgE-mediated cross-linking of the high affinity IgE receptor (FceRI). These include antibodies against CD164 (WS-80160, clone N6B6 and WS-80162, clone 67D2), as well as two reagents with previously unknown specificities that were identified as CD13 (WS-80274, clone A8) and CD107a (WS-80280, clone E63-880). The activation patterns followed either the "CD203c-like" or "CD63-like" activation profile. The CD203c profile is characterized by a rapid and significant upregulation (of CD13, CD164, and CD203c), reaching maximum levels after 5-15 min of stimulation. The Phosphoinositide-3-kinase (PI3K)-specific inhibitor Wortmannin inhibited the upregulation of these markers whereas 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced a rapid and FceRI-independent upregulation within 1-2 min. In the CD63 profile, maximum upregulation (of CD63 and CD107a) was detected only after 20-40 min, and upregulation by TPA reached maximum levels after 60 min. In summary, our data identify CD13, CD107a, and CD164 as novel basophil-activation antigens. Based on time kinetics of upregulation, we hypothesize that molecules of the "CD203c group" and the "CD63 group" are linked to two different mechanisms of basophil activation.

The diagnostic interpretation of basophil activation test in immediate allergic reactions to betalactams

BACKGROUND

Basophil activation by allergens, including drugs, has been used to determine sensitivity and to study IgE recognition and cross-reactivity.

OBJECTIVE

We sought to determine the sensitivity and specificity of a basophil activation test (Basotest) in patients with immediate allergic reactions to betalactams, with a later comparison between patients who were selective (those recognizing the culprit drug excluding benzylpenicillin (BP)) and cross-reactors (those recognizing several penicillin determinants including BP).

METHODS

Basotest to different haptens was performed in 70 patients with immediate allergic reactions to betalactams, classified into three groups: (A) skin test positive independently of CAP/RAST immunoassay value, (B) skin test negative and CAP/RAST positive, and (C) skin test and CAP/RAST negative but drug provocation test positive. Basotest was carried out by flow cytometry following the manufacturer's instructions using different betalactam determinants and results expressed as a stimulation index.

RESULTS

Of the 70 patients, 34 (48.6%) were positive to Basotest (sensitivity: 48.6%), 31 (44.3%) to CAP/RAST and 46 (65.7%) to either one or the other. Considering the different groups, Basotest was positive in 50.9% of patients in Group A, 60% in Group B and 14.3% in Group C. The specificity was 91.3%. Positivity to the haptens was 28.6% to amoxicillin (AX), 21.7% to BP, 20% to benzylpenicilloyl-poly-l-lysine, 12.5% to ampicillin and 2.2% to minor determinant mixture. In patients with cephalosporin reactions, Basotest to the culprit cephalosporin was positive in 77.7%. There were differences between the two reactor groups in the sensitivity of Basotest (selective to AX=50%, cross-reactors=28.6%; chi(2)=10.809, P=0.004) and in the CAP/RAST (selective to AX=28.6%, cross-reactors=61.9%; chi(2)=8.944, P=0.011).

CONCLUSIONS

The sensitivity of Basotest is similar to immunoassays (CAP/RAST). Sensitivity is improved when used in combination. Although further studies are required, Basotest results for cephalosporin allergy seem very promising. This technique does not help differentiate between selective reactors and cross-reactors.

CD63 expression on basophils as a tool for the diagnosis of pollen-associated food allergy: sensitivity and specificity

BACKGROUND

Basophil activation is associated with the expression of CD63. Because allergens can induce basophil activation by cross-linking specific IgE, increased CD63 expression has been proposed as a novel in vitro test for immediate type allergy.

OBJECTIVE

We compared the CD63-based basophil activation test (BAT) in the diagnosis of allergy to carrot, celery and hazelnut with skin prick tests (SPT) and measurement of allergen-specific IgE.

METHODS

Twenty-nine patients with a history of an oral allergy syndrome induced by carrot, celery or hazelnut (n = 20 for each allergen) and 20 controls were studied. SPT were performed with standardized and native carrot, celery and hazelnut extracts. Allergen-specific IgE was determined by the CAP FEIA method and basophil activation was determined by flow cytometry upon double staining with anti-IgE/anti-CD63 mAb.

RESULTS

SPT with native carrot, celery and hazelnut showed sensitivities of 100%, 100% and 90%, and specificities of 80%, 80% and 90%. SPT with commercial extracts of the same allergens gave sensitivities of 85%, 80% and 85%, and specificities of 80%, 80% and 90%. Sensitivity of allergen-specific IgE and the BAT for carrot, celery and hazelnut was 80% vs. 85%, 70% vs. 85%, and 80% vs. 90%, with corresponding specificities of 80% vs. 85%, 80% vs. 80%, and 95% vs. 90%. The cut-off for a positive BAT was 10% CD63+ basophils. Moreover, there was a positive correlation between IgE reactivity and the number of CD63+ basophils for all food allergens (carrot: r = 0.69, celery: r = 0.67, hazelnut: r = 0.66).

CONCLUSIONS

Quantification of basophil activation by CD63 expression is a valuable new in vitro method for diagnosis of immediate type food sensitization. Although double-blind placebo-controlled food challenges remain the gold standard, the CD63-based BAT may supplement routine diagnostic tests such as SPT or allergen-specific IgE in the future.

Flow cytometry versus histamine release analysis of in vitro basophil degranulation in allergy to Hymenoptera venom

BACKGROUND

Flow cytometry (FCM) has been proposed for specific allergy in vitro testing. We investigated its biological significance for allergy to Hymenoptera venoms and compared it with the routinely performed basophil histamine release test (HRT).

METHODS

Blood samples from 26 allergic and 8 nonallergic donors were incubated with venom at serial concentrations. Basophils were analyzed with anti-CD45-PE-Cyanin 5, Anti-IgE-FITC, and Anti-CD63-Phycoerythrine. HRT was measured by radioimmunoassay.

RESULTS

FCM was as convenient as HRT for measuring basophil reactivity in at least 87% of allergic and 75% of nonallergic subjects. CD63 outer expression was specifically induced in 91% of releaser subjects (86% on HRT) and in 1 of 10 tests in nonallergic donors, or one of six tests (16% on HRT) in allergic patients tested with an irrelevant allergen. Both methods were concordant in 85.7% of the tests. The three discordant patients had low-grade reactions and borderline biological responses on FCM (n = 2) or HRT (n = 1).

CONCLUSIONS

The dynamic, physiologic significance of CD63, the dose-response curve, and dependency on ethylene-diaminetetra acetic acid suggested that both tests reflect the same mechanism.

Marked improvement of the basophil activation test by detecting CD203c instead of CD63

BACKGROUND

The flow cytometric basophil activation test by detection of CD63 expression has been developed as an alternative method for in vitro diagnosis of IgE-mediated reactions to various allergens. Despite promising initial studies, the test remains disappointing in terms of sensitivity. CD203c has recently been demonstrated as a specific activation marker of basophils that is rapidly up-regulated after allergen challenge in sensitized patients.

OBJECTIVE

The goal of the present study was to compare basophil activation tests by using either CD203c or CD63 in the diagnosis of immediate-type allergy to latex.

METHODS

Twenty-seven patients (health care workers of our institution) who developed clinical features evocative of allergy after contact with latex were included and classified into two groups. Group 1 (n = 16) comprised true allergic patients who presented with typical signs of immediate allergic reaction associated with a positive skin test (prick test). Group 2 (n = 11) consisted of patients whose clinical history was not typical and had negative skin test. Twelve healthy subjects were also studied as controls. We compared the sensitivity of two triple-staining flow cytometric protocols measuring basophil activation after latex stimulation: CD45-IgE-CD63 and CD45-IgE-CD203c.

RESULTS

The CD203c protocol showed a higher sensitivity than the CD63 protocol (75% vs. 50%). In comparison, latex-specific IgE sensitivity was found to be 69%. Furthermore, the magnitude of the basophil response was significantly higher with CD203c in comparison with CD63. Specificity was 100% for both protocols.

CONCLUSION

Due to superior gating of basophils and a higher range of activation in response to allergen, the basophil activation test is markedly improved by use of CD203c instead of CD63.

Monitoring of basophil activation using CD63 and CCR3 in allergy to muscle relaxant drugs

Allergic or pseudoallergic reactions that occur during anesthesia have been increasing for the last few years. To date, the diagnosis of allergy to muscle relaxants remains difficult. In this respect, we developed a flow cytometric method for the study of drug-induced basophil degranulation using CD63 and CCR3. Fifty patients who developed clinical features evocative of allergic reactions immediately after induction of anesthesia were included and classified into two groups. Group 1 (n = 39) comprised true allergic patients, who developed typical signs of shock associated to positive skin testing. Group 2 (n = 11) consisted of patients whose clinical history was not typical and skin testing was negative or nonconclusive. Seventeen control subjects were also studied in this report. We compared data from flow cytometry to skin tests, specific IgE, and histamine release results. Flow cytometry showed a sensitivity of 54%, while that of specific IgE was similar, at 62%. Interestingly, when considering the sensitivity of IgE + CD63 for diagnosis, we reached a sensitivity value of 80%. Of 15 negative results for specific IgE, we found 7 positive CD63 tests, while histamine release gave positive results in only 2 cases. Furthermore, the CD63 protocol showed good specificity (100%). We conclude that our flow cytometry protocol is a promising tool in allergy diagnosis since it is specific and complementary to specific IgE detection.

Allergen-induced basophil activation: CD63 cell expression detected by flow cytometry in patients allergic to Dermatophagoides pteronyssinus and Lolium perenne

BACKGROUND

In this study, we determined by flow cytometry the percentage of basophils activated after in vitro stimulation by allergens and expressing the CD63 marker. The diagnostic reliability of the technique was assessed as well as its correlation with other in vitro diagnostic parameters.

METHODS

Fifty-three patients suffering from asthma and/or allergic rhinitis following sensitization to Dermatophagoides pteronyssinus and 51 patients sensitized to Lolium perenne were investigated. Twenty-four atopic patients not sensitive to these allergens and 38 healthy subjects were also selected as controls. The basophil activation test determines the percentage of basophils which express CD63 as an activation marker, by means of flow cytometry, after in vitro stimulation with allergen, using double labelling with monoclonal antibody anti-CD63-PE and anti-IgE-FITC.

RESULTS

No differences in basal values (non-activated control) were found between sensitized patients, atopic controls and healthy controls. On the other hand, sensitized patients showed a significantly higher percentage of activated basophils after stimulation by allergens in vitro than both control groups (P < 0.001). We found a significant correlation between skin tests and basophil activation tests (r = 0.72, P < 0.001). We also found a positive and significant correlation between basophil activation tests and histamine release tests (r = 0.80, P < 0.001), allergen-specific sulphidoleukotriene production (r = 0.7, P < 0.001) and the occurrence of serum allergen-specific IgE (r = 0.71, P < 0.001).

CONCLUSION

The basophil activation test is a highly reliable technique in the diagnosis of allergy to inhalant allergens. The sensitivity of the basophil activation test was 93.3%, and its specificity 98.4%, when using a cut-off point of 15% activated basophils as positive result.

Surface membrane antigen alteration on blood basophils in patients with Hymenoptera venom allergy under immunotherapy

BACKGROUND

Venom immunotherapy (VIT) provides widespread protection against systemic anaphylactic reactions after a sting of the respective insect. This effect is attributed to a shift from T(H)2 to T(H)1. However, because basophils also produce and release cytokines, such as IL-4 and IL-13, they may be part of the cytokine network. The cytokines may regulate basophilic granulocytes, as suggested by the presence of cytokine receptors IL-2Ralpha, GM-CSFRalpha, IL-1RII, IL-3R, IL-4R, IL-5R, and IL-6R on basophils from nonallergic donors.

OBJECTIVE

The purpose of this study was to demonstrate that human basophils from subjects allergic to wasp venom undergoing VIT are regulated by cytokines, as shown by the alteration of the expression of cytokine receptors (and other markers).

METHODS

The expression of the surface interleukin receptors and activation antigens on basophils from 19 nonallergic subjects and 48 patients with wasp venom allergy was investigated before, immediately after, and 1 week after VIT (20 patients only).

RESULTS

Basophilic granulocytes in allergic subjects, compared with those in healthy persons, showed elevated expression of CD32 (FcgammaRII), CD122 (IL-2Rbeta), CD124 (IL-4Ralpha), CD130 (IL-6 and 11Rbeta), CD154 (CD40L), and HLA-DR. Activation of basophils clearly increased during VIT indicated by increased expression of CD32, CD33, CD35 (CR1), CD63, CD116 (GM-CSFRalpha), CD122, CD124, CD130, and CD154. HLA-DR expression also tended to increase. The expression of IL-5R (CD125) decreased. A significant decrease of the basophilic surface antigens CD11c, CD32, CD35, CD63, CD116, CD122, CD124, CD130, and CD132 (interleukin receptor gamma) was detected 1 week after the end of rush VIT.

CONCLUSION

The rise in CD63 during VIT indicates a partial basophil degranulation with release of stored protein mediators, including IL-4. IL-4 may cause a transient upregulation of different surface antigens in an autocrine manner. Thereafter, cytokines released by T cells, which as a result of VIT have changed from a T(H)2 type to a more T(H)1 type, downregulate the activation of the basophilic granulocytes.

Diagnosis of venom allergy by flow cytometry. Correlation with clinical history, skin tests, specific IgE, histamine and leukotriene C4 release

BACKGROUND

Potent allergens such as hymenoptera venoms are capable of inducing severe and life threatening clinical reactions. Percentage of false negative results obtained by the usual diagnostical methods is comprised between 10 and 25%.

OBJECTIVE

Evaluation of the sensitivity and the specificity of cellular tests and particularly evaluation of a new flow cytometric method.

METHODS

Forty-five allergic patients having experienced a local, a systemic reaction or an anaphylactic shock and 10 controls having undergone hymenoptera stings without clinical reactions were selected on the basis of the clinical history, skin tests and specific IgE. Three cellular tests were performed on the same cell suspensions and in the presence of 2 ng/mL of rIL3: histamine release (RIA), leukotriene C4 release (ELISA) and basophil activation test (flow cytometry after double anti-IgE FITC, anti-CD63 PE labelling).

RESULTS

As compared to the clinical history, sensitivities of skin tests, specific IgE, flow cytometry, histamine release and leukotriene release were, respectively; 85%, 88%, 100%, 89% and 100%. Flow cytometric analysis of basophil activation showed a significant decrease of the mean fluorescence density and number of IgE positive cells and a significant increase of the number of CD63 positive cells. The 10 controls tested by flow cytometry were negative.

CONCLUSION

As compared to the clinical history and to the other parameters tested here, flow cytometry showed a high sensitivity and a high specificity. The excellent correlation observed between this method and the other cellular tests such as histamine and leukotriene release are in favour of the specificity of flow cytomery and in favour of the use of this method for venom allergy diagnosis.

Cutting edge: differential production of prostaglandin D2 by human helper T cell subsets

Several effector molecules, including cytokines, are differentially produced by Th1 and Th2 cells. We used a gene expression screen method to identify a gene encoding hematopoietic PG D synthase (hPGDS) which was preferentially expressed in human Th2 but not Th1 clones. Studies with anti-hPGDS mAbs confirmed the Th2-dominated expression of hPGDS protein. Upon stimulation with anti-CD3 plus anti-CD28 mAbs, coordinated cyclooxygenase-2 expression and PGD2 production were induced in Th2 lines. hPGDS expression was also observed in a small population (<1.0%) of peripheral blood CD4+ lymphocytes from healthy adults. Most hPGDS-expressing CD4+ lymphocytes showed a typical Th2-type cytokine pattern. Our results suggest that, at the sites of Ag presentation, at least part of the Th2 cell population produces PGD2, which may be involved in various aspects of Th2-related immune responses similar to mast cells.

In vitro diagnosis of cypress pollen allergy by using cytofluorimetric analysis of basophils (Basotest)

BACKGROUND

Cupressaceae pollen allergy is a worldwide pollinosis, but its in vitro diagnosis is notoriously difficult. The Basotest is a newly available in vitro test for the detection of allergen-specific IgE based on the level of cellular activation of basophils by using flow cytometry.

OBJECTIVES

The Basotest was compared with the measurement of cypress pollen-specific IgE in highly selected patients.

METHODS

We analyzed 34 patients allergic to cypress pollen selected on the basis of a suggestive clinical history and positive skin test and nasal challenge responses to cypress pollen extract. We also analyzed 8 patients with positive skin test responses to cypress pollen extract who did not present symptoms during the pollen season (intermediate group) and 33 control subjects. Sensitivity, specificity, and efficiency of the Basotest and serum-specific IgE levels measured by using the CAP System were determined in patients allergic to cypress pollen. Histamine release was studied in a selected group of patients.

RESULTS

The Basotest was more sensitive (91.2%) than the CAP System (76%) for the in vitro diagnosis of cypress pollen allergy. A dose-response curve was observed in basophils obtained from patients allergic to cypress pollen. There were no false-positive results with either test (specificity 100%). The results of the Basotest or those of the CAP System did not correlate with the patients' in vivo threshold sensitivity assessed by skin tests and nasal challenge.

CONCLUSIONS

The Basotest was found to be an effective diagnostic test in patients allergic to cypress pollen.

Simplified purification of human basophils

Studies of human basophils have been limited by the low number present in peripheral blood and the difficulties of purification to homogeneity with reasonable yield and functional status. Reproducible purification of human basophils to 96.5+/-0.5% with a yield of 40.8+/-5.3% was obtained by negative selection using immunomagnetic beads following initial separation by density gradient centrifugation. Isolated cells demonstrated complete viability by vital dye exclusion and spontaneous histamine release following incubation of <5%. Stimulation with anti-IgE or calcium ionophore A23187 caused histamine release and leukotriene C(4) production. Basophils demonstrated dose-dependent chemotaxis to monocyte chemotactic protein-3. This simplified methodology results in fully functional basophils in very high purity and good yield.

CRTH2, an orphan receptor of T-helper-2-cells, is expressed on basophils and eosinophils and responds to mast cell-derived factor(s)

We have recently cloned a putative chemoattractant receptor, named CRTH2, which is preferentially expressed on human T-helper- (Th) 2 but not Th1 cells. In this study, we demonstrated that CRTH2 is also highly expressed on peripheral blood basophils and eosinophils. Our search for a CRTH2 ligand identified mast cells as the possible producers of a ligand. When stimulated with an anti-FcepsilonR1 antibody, cord blood-derived mast cells secreted factor(s) that induced Ca(2+) mobilization in CRTH2-expressing K562 cells but not in mock transfected cells. These findings implied the involvement of CRTH2 in mast cell-mediated immune responses such as allergic reactions.

Detection of allergen-induced basophil activation by expression of CD63 antigen using a tricolour flow cytometric method

In the field of allergy diagnosis, most in vitro functional tests are focused on basophils. Nevertheless, the very small number of circulating basophils limits these experiments and their clinical benefit remains controversial. As flow cytometry is a valuable tool for identifying cell populations, even at low concentrations, we developed a tricolour flow cytometric method for the study of allergen-induced basophil activation. Identification of cells was based both on CD45 expression and on the presence of IgE on the cell surface, since basophils express high-affinity receptors for IgE (Fc epsilon RI). Cell activation upon allergen challenge was assessed by the expression of CD63 antigen on the plasma membrane. Basophil isolation and activation (with the chemotactic peptide formyl-methionyl-leucyl-phenylalanine) were validated in 32 non-allergic patients. In 12 allergic patients, basophil stimulation by a relevant allergen was in most cases positive (10/12). Furthermore a concentration-dependent hook effect was observed. Of the allergic and non-allergic patients, none showed non-specific activation with an irrelevant allergen (specificity 100%). Overall, our preliminary results, even in a small population, suggest that this is a reliable and valuable method for the diagnosis of allergies complementing specific allergen IgE and skin test results. Obviously, additional clinical studies are needed to validate these first results.

Human basophil activation measured by CD63 expression and LTC4 release in IgE-mediated food allergy

BACKGROUND

IgE-dependent basophil activation induced by an allergen elicit the release of LTC4 and the expression of the CD63 membrane marker.

OBJECTIVE

The aim of this study was to check if flow cytometric analysis of basophil activation could be applied to food allergy diagnosis and if this method paralleled LTC4 release.

METHODS

Patients were selected by the clinical history, skin tests, and provocation tests. Basophil activation induced by food extracts was studied in 24 control subjects and in 27 patients having a food allergy by LTC4 release test (LRT) and by flow cytometric anti-IgE+, CD63 + cell counting (BAT = basophil activation test). In case of negative anti-IgE response a passive blood donor basophil passive sensitization step was added to LRT and BAT. Leucocyte histamine release test was performed in 11 patients.

RESULTS

Basophil activation test was positive in 18/31 cases and LRT in 22/34 cases for food-allergic patients and, respectively, in 1/33 and 1/35 cases for the controls. A correlation was observed between specific IgE, BAT, and LRT. Basophil activation test and LRT performed after passive sensitization had an excellent sensitivity only for specific IgE levels ranging between 3.5 and 35 KU/L.

CONCLUSION

The present study shows that allergen-induced LTC4 release and anti-IgE, antiCD63 bicolor flow cytometric analysis of basophil activation may be used for food allergy diagnosis. Both tests have a good sensitivity and specificity. Basophil activation test and LRT are more efficient than histamine release test in case of high spontaneous histamine release, frequently observed in case of food allergy.

Passive antibody transfer on human leukocytes: application to small animal allergy diagnosis by flow cytometry

Animal allergy diagnosis is based mainly on clinical history, skin tests and, at least for dogs, specific IgE antibodies. The quality of anti-canine IgE antibodies is variable and monoclonal antibodies have been recently characterized. The allergen panel tested in humans and in dogs is similar except for flea and for Staphylococcus. Allergen-induced basophil activation may be measured by the release of mediators such as histamine and leukotriene C4 and by the expression of the CD63 marker on basophil membrane. This latter method is based on the flow cytometric analysis of leukocyte suspensions after double anti-IgE FITC, anti-CD63 PE labelling of human basophils, and has been validated for aero-allergens, food allergens, venoms and several drugs for human allergy diagnosis. After having demonstrated that, in the dog, anaphylactic anti- bodies were capable of binding to human basophil high-affinity receptors for IgE, we went up a flow cytometric method for animal allergy diagnosis based on passive sensitization of human basophils. Prelim- inary results obtained by this method for allergens such as house dust mite or pollen were very encouraging. This method is faster and less expensive than the methods based on mediator release but is still dependent on the availability of fresh human leukocytes. This method may represent a new sensitive and specific method for animal allergy diagnosis.

Flow cytometric monitoring of allergen induced basophil activation

Human basophils express many clustered differentiation antigens (CD), including CD45; however, none are specific for these cells. In a previous study, we described a two-color immunofluorescence procedure, employing antibodies to CD45 and IgE for the cytometric evaluation of basophils. In the present work, we show that when sensitized basophils are stimulated by allergenic preparations, they demonstrate an upregulation of CD45 as well as a decrease in anti-IgE binding. Since CD45 antigen modulation was observed with all aeroallergens tested and the decrease in IgE expression varied with allergenic preparations, the measurement of CD45 upregulation was used to evaluate basophil activation. Using this approach, reproducible results were observed when atopic patients were tested at different time intervals. In addition, we show that the upregulation of CD45 on allergen stimulated basophils is a very rapid phenomenon that is observed after a few minutes and that this rapid flow cytometric method can also be used for investigations on nonallergenic mediators of basophil stimulation such as calcium ionophores.

Immunologic differentiation of absolute lymphocyte count with an integrated flow cytometric system: a new concept for absolute T cell subset determinations

We describe a method to obtain results for immune status monitoring that uses a three-test panel, comprised of isotype control and 2 specific Mab tests (CD4/CD8/CD3 and CD16/CD19/CD3), in conjunction with a flow cytometer that directly measures absolute counts. Automated software is used for lineage-specific gating of three-color immunofluorescence to determine lymphocyte and lymphocyte subset counts. The autogating function of this software is shown to yield equivalent results to manual analysis by an expert user, and to be effective when as few as 25 target cells are present. The software is also shown to perform automatic quality control checks of the sample preparation, reagent, and automated analysis. We demonstrate that the sum of T (CD3+), B (CD19+), and natural killer (NK, CD16 + CD3-) cells, as a determination of all lymphocytes, correlates well with lymphocytes measured using a light scatter differential. Moreover, T + B + NK lymphocyte count is shown to be less error-prone than lymphocyte count from light scatter differential, and to minimize errors that arise from between-technician variation in sample preparation. Our data suggest that the new approach that we describe could offer an alternative to the traditional two-stage methods for measuring absolute counts of lymphocyte subsets for immune status monitoring. As such this method could reduce, through objective automated analysis, testing cost and complexity, without sacrificing the quality of results.