Nonreleasing basophils convert to releasing basophils by culturing with IL-3

Translating the biology of β common receptor-engaging cytokines into clinical medicine

The family of cytokines that comprises IL-3, IL-5, and GM-CSF was discovered over 30 years ago, and their biological activities and resulting impact in clinical medicine has continued to expand ever since. Originally identified as bone marrow growth factors capable of acting on hemopoietic progenitor cells to induce their proliferation and differentiation into mature blood cells, these cytokines are also recognized as key mediators of inflammation and the pathobiology of diverse immunologic diseases. This increased understanding of the functional repertoire of IL-3, IL-5, and GM-CSF has led to an explosion of interest in modulating their functions for clinical management. Key to the successful clinical translation of this knowledge is the recognition that these cytokines act by engaging distinct dimeric receptors and that they share a common signaling subunit called β-common or βc. The structural determination of how IL-3, IL-5, and GM-CSF interact with their receptors and linking this to their differential biological functions on effector cells has unveiled new paradigms of cell signaling. This knowledge has paved the way for novel mAbs and other molecules as selective or pan inhibitors for use in different clinical settings.

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.

Purification of Basophils from Peripheral Human Blood

The purification of basophils from peripheral blood has represented a formidable challenge for researchers since they were discovered by Paul Ehrlich in 1879. From the first published attempts in the late 1960s, it took half a century to develop robust protocols able to give sufficient numbers of pure, functionally unimpaired basophils. The existing protocols for basophil purification exploit those properties of basophils which distinguish them from other cell types such as their localization in blood, density, and the presence or absence of surface markers. Purification techniques have been used in various combinations and variations to achieve a common goal in mind: to obtain a pure population of human basophils in sufficient numbers for downstream studies. The arduous way leading up to the modern protocols is summarized in this historical retrospective. A fast protocol for purification of basophils to near homogeneity is also described.

Mast cells derived from human induced pluripotent stem cells are useful for allergen tests

BACKGROUND

Several methods have been developed to detect allergen-specific IgE in sera. The passive IgE sensitization assay using human IgE receptor-expressing rat cell line RBL-2H3 is a powerful tool to detect biologically active allergen-specific IgE in serum samples. However, one disadvantage is that RBL-2H3 cells are vulnerable to high concentrations of human sera. Only a few human cultured cell lines are easily applicable to the passive IgE sensitization assay. However, the use of human induced pluripotent stem cells (iPSCs) to generate human mast cells (MCs) has not yet been reported.

METHODS

The nuclear factor-kappa B (NF-κB)-responsive luciferase reporter gene was stably introduced into a human iPSC line 201B7, and the transfectants were induced to differentiate into MCs (iPSC-MCs). The iPSC-MCs were sensitized overnight with sera from subjects who were allergic to cedar pollen, ragweed pollen, mites, or house dust, and then stimulated with an extract of corresponding allergens. Activation of iPSC-MCs was evaluated by β-hexosaminidase release, histamine release, or luciferase intensity.

RESULTS

iPSCs-MCs stably expressed high-affinity IgE receptor and functionally responded to various allergens when sensitized with human sera from relevant allergic subjects. This passive IgE sensitization system, which we termed the induced mast cell activation test (iMAT), worked well even with undiluted human sera.

CONCLUSIONS

iMAT may serve as a novel determining system for IgE/allergens in the clinical and research settings.

Pros and Cons of Clinical Basophil Testing (BAT)

PURPOSE OF REVIEW

We review basophil testing by flow cytometry with an emphasis on advantages and disadvantages.

RECENT FINDINGS

There are many tools available to assess the presence and severity of allergic diseases in patients. For 50 years, peripheral blood basophils have been used as tools to study these diseases. It is a very accessible cell that binds IgE antibody and secretes the classical mediators responsible for the symptoms of allergic reactions. In the last decade, an even more accessible methodology, using flow cytometry, has been developed to enhance the ability to use basophils for both mechanistic and clinical diagnostics. Basophil testing has been included in diagnostics for different forms of allergies as well as to monitor disease status. A variety of studies have begun to establish both precise methods and their clinical relevance for disease diagnosis, but there remain some important questions on how to take optimal advantage of the behaviours of basophils.

Systematic characterization of basophil anergy

BACKGROUND

Cohort studies indicated that in certain individuals the basophils do not respond toward allergens due to a desensitization of their Fc epsilon receptor pathway. Cause and functional role as well as the implications on allergic reactions, however, are not clear yet.

METHODS

A cross-sectional study was carried out in the tropical urban environment of Singapore, where the allergic response is dominated by a single allergen (house dust mite; HDM). Blood samples were collected from 476 individuals and analyzed comprehensively to correlate the functional state of their basophils with the clinical state as well as the composition of the cellular and soluble plasma components.

RESULTS

Inactivation of basophils ('basophil anergy') was observed in about 10% of the cohort. It was associated with a downregulation of basophil Syk and an apparent reduction in the incidence of allergic rhinitis. Correlations on the cohort level suggest that it represents a transitional state to be passed through during the interconversion of responder and nonresponder state.

CONCLUSIONS

Basophil anergy thus seems to function as activation barrier to prevent unwanted reactions against minor allergens. It may therefore be relevant for diagnostic purposes or therapeutic interventions of allergic diseases.

Expression profiling of human basophils: modulation by cytokines and secretagogues

Human basophils are an accessible participant of the human allergic reaction. There is natural variation in various functional endpoints and in signaling molecule expression but there has been only a limited effort to place this information in the context of mRNA expression profiles. This study examined the hypothesis that unique mRNA signatures could be identified during the response of human basophils to several known forms of stimulation. Highly purified human basophils were cultured in vitro and exposed to IL-3, IL-5, NGF, IL-33, IL-2, anti-IgE Ab, or FMLP and the mRNA profiles examined by microarrays. The response to IL-3 and anti-IgE Ab were examined on 2–3 time frames and the response to IL-3 examined at several concentrations. In addition, the mRNA signatures of 3 different potential phenotypes were examined. These included basophils with the so-called non-releaser phenotype, and basophils from atopic and non-atopic subjects. Given the role of IL-3 in basophil maturation and the known profound effects on mature basophil function, it was not surprising that IL-3 showed the greatest influence on the basophil transcriptome. However, it also became apparent that the act of isolating and culturing basophils was sufficient to induce a large number of changes in the transcriptome, despite high viability and recovery. These “culture-effect” changes dominated the changes in mRNA profiles induced by other stimuli. Unique signatures for anti-IgE antibody and IL-33 could be identified although the number of gene transcripts (6–30) that were unique to these two stimuli was very limited. There were no apparent unique profiles for IL-5, NGF, IL-2 or FMLP. Therefore, a potential tool for screening basophil phenotypes was limited to changes that could be induced by IL-3 (or no IL-3), IL-33 and anti-IgE Ab.

Subthreshold desensitization of human basophils re-capitulates the loss of Syk and FcεRI expression characterized by other methods of desensitization

BACKGROUND

Clinical desensitization of patients to drugs involves progressive exposure to escalating doses of drug over a period of 24 h. In prior studies, this method was re-capitulated in vitro to also demonstrate loss of mast cell or basophil responsiveness. However, most signalling studies of human basophils have identified changes in signalling by using other methods of inducing cellular desensitization.

OBJECTIVE

This study examined two well-described endpoints of basophil desensitization, loss of syk or FcεRI expression, under conditions of subthreshold desensitization.

METHODS

The loss of FcεRI and syk was examined in human basophils.

RESULTS

It was shown that both loss of syk and FcεRI/IgE occurred during an escalating series of stimulation (anti-IgE Ab) and that expression loss occurred despite the presence of little histamine release. If basophils were first cultured for 3 days in 10 ng/mL IL-3, the concentration-dependence of histamine release shifted to 100-fold lower concentrations of stimulus. However, loss of syk did not show any change in its EC50 while loss of FcεRI also shifted 100-fold. From the perspective of early signal element activation, the marked shift in the EC50 for histamine release was not accompanied by similar shifts in the EC50s for several signalling elements. The EC50s for phospho-Src, phospho-SHIP1, phospho-Syk, or phospho-Cbl did not change while the EC50s for phospho-Erk and the cytosolic calcium response did shift 100-fold.

CONCLUSIONS

These studies show that under normal conditions, subthreshold desensitization leads to loss of two critical signalling molecules (FcεRI and syk) but under at least one condition, treatment with IL-3, it is possible to markedly blunt the loss of syk, but not FcεRI, while executing a proper subthreshold titration. These data also suggest that IL-3 modifies only the sensitivity of signalling elements that are downstream of syk activation.

A case of anaphylactic reaction following matsutake mushroom ingestion: demonstration of histamine release reaction of basophils

BACKGROUND

Matsutake mushroom is not recognized as a common food allergen. However, several case reports have suggested that this mushroom can induce anaphylaxis on rare occasions.

CASE SUMMARY

We report a woman with bronchial asthma, who experienced two episodes of Matsutake-induced anaphylaxis. Both the prick-to-prick test and basophil histamine release test showed positive reactions to this mushroom in this patient, but not in control subjects.

DISCUSSION

Matsutake mushroom can, on rare occasions, cause anaphylaxis in sensitized people, a reaction so far observed only in Japan. Not ony the in vivo prick-to-prick test but also the in vitro basophil activation test utilizing the patient's blood represent useful methods for allergen identification and also for identification of sensitized subjects.

Validation of basophil CD164 upregulation for pollen allergy diagnosis

The aim of the study was to evaluate the sensitivity and specificity of allergen-induced basophil CD164 upregulation in patients with seasonal allergic rhinitis caused by allergy to grass pollens. This study was performed in 24 patients with allergy to grass pollens, and in 25 healthy controls. The protocol for allergen-induced basophil CD164 upregulation consisted of whole blood samples processing and staining with anti-CCR3/anti-CD164 antibodies added to a buffer at the beginning of stimulation. We observed dose-dependent allergen-induced basophil CD164 upregulation with 100% of specificity in both used allergen concentrations (12 and 1.2 ng/ml). Higher allergen concentration resulted in 100% and lower concentration in only 70.83% sensitivity. We have observed in the patients statistically significant correlations between anti-IgE stimulation and both allergen concentrations (for 12 ng/ml, r = 0.71, p < 0.0001; and for 1.2 ng/ml, r = 0.64, p < 0.001). We conclude that assessment of allergen-induced basophil CD164 upregulation is a very useful method for in vitro determination of allergy to grass pollens. This method seems to be a very promising tool in laboratory testing of allergies to other allergens.

Regulation of Syk kinase and FcRbeta expression in human basophils during treatment with omalizumab

BACKGROUND

In human basophils from different subjects, maximum IgE-mediated histamine release and the level of Syk protein expression correlate well. Recent studies suggest that in some patients treated with omalizumab, the response to stimulation with anti-IgE antibody increases. In unrelated studies there is also evidence that the composition of FcepsilonRI in basophils differs among subjects. This observation raised the possibility that the stoichiometry of FcRbeta/FcepsilonRIalpha is not fixed to a 1:1 ratio and might be modifiable during changes in the basophil's environment.

OBJECTIVE

We sought to determine whether treatment with omalizumab results in increases in Syk expression and anti-IgE-mediated histamine release and disproportionately alters the relative presence of FcRbeta and FcepsilonRIalpha.

METHOD

Syk, FcepsilonRIalpha, and FcRbeta expression was monitored during the treatment of subjects with omalizumab.

RESULTS

Treatment with omalizumab reduced histamine release from peripheral blood leukocytes stimulated with cat allergen in vitro, but histamine release stimulated with anti-IgE antibody increased 2-fold. Expression of Syk increased 1.86-fold. There was no change in the expression of c-Cbl, a signaling element that is sensitive to the presence of IL-3, and no increase in response to formyl-met-leu-phe (tripeptide), a response that also increases in the presence of IL-3. There was a 60% decrease in the FcRbeta/FcepsilonRIalpha ratio in patients treated with omalizumab.

CONCLUSIONS

In the context of previous studies, these studies provide support for a proposal that Syk expression is modulated in vivo through an IgE-dependent mechanism and that the ratio of FcepsilonRI alpha and beta subunits in basophils is influenced by factors extrinsic to the cell.

Syk expression in peripheral blood leukocytes, CD34+ progenitors, and CD34-derived basophils

In human basophils from different subjects, maximum IgE-mediated histamine release and the level of syk protein expression correlate well. It is not clear when in the basophil's lifetime the set-point for syk expression is reached or how expression levels are determined for a given individual. An examination of syk expression in peripheral blood eosinophils, neutrophils, monocytes, B and T cells, DCs, and NK cells showed that with the exception of T cells, basophils were unique in expressing low levels of syk. No correlations were observed between syk expression in basophils and other types of leukocytes, suggesting a unique mechanism of regulation for basophils. The expression level of syk in CD34+ progenitors was approximately 11-fold higher than in peripheral blood basophils, and it remained at this level during maturation of the cells in IL-3 to a cell with characteristics of peripheral blood basophils. Down-regulation of syk expression in the culture-derived basophils was induced by culturing under conditions of chronic aggregation of FcepsilonRI. Syk was down-regulated to peripheral blood basophil levels in 50% of the cells. Despite the chronic aggregation of FcepsilonRI, the cells retained the same expression of FcepsilonRI, histamine content, and morphological staining of granules as cells not experiencing chronic aggregation. These results suggest that chronic stimulation through FcepsilonRI during basophil maturation might be a mechanism for down-regulating syk expression, while retaining other characteristics associated with mature peripheral blood basophils.

Human basophils and cytokines/chemokines

Basophils comprise the smallest population in human peripheral blood leukocytes. The role of basophils in the pathogenesis of allergic diseases has long been obscure, although their accumulation and activation in tissues have suggested their potential importance. Recent advances in the field of basophil biology have indicated that cytokines and chemokines are the primary regulators of basophil functions. In addition, various functions of these cells seem differently modulated. The evidence strongly supports the notion that basophils exposed to these substances and allergens will behave as unique effector cells that presumably play proinflammatory roles in type I allergic reactions.

Histamine-releasing factor/translationally controlled tumor protein (HRF/TCTP)-induced histamine release is enhanced with SHIP-1 knockdown in cultured human mast cell and basophil models

Previously, we demonstrated a negative correlation between histamine release to histamine-releasing factor/translationally controlled tumor protein (HRF/TCTP) and protein levels of SHIP-1 in human basophils. The present study was conducted to investigate whether suppressing SHIP-1 using small interfering (si)RNA technology would alter the releasability of culture-derived mast cells and basophils, as determined by HRF/TCTP histamine release. Frozen CD34+ cells were obtained from the Fred Hutchinson Cancer Research Center (Seattle, WA, USA). Cells were grown in StemPro-34 medium containing cytokines: mast cells with IL-6 and stem cell factor (100 ng/ml each) for 6-8 weeks and basophils with IL-3 (6.7 ng/ml) for 2-3 weeks. siRNA transfections were performed during Week 6 for mast cells and Week 2 for basophils with siRNA for SHIP-1 or a negative control siRNA. Changes in SHIP-1 expression were determined by Western blot. The functional knockdown was measured by HRF/TCTP-induced histamine release. siRNA knockdown of SHIP-1 in mast cells ranged from 31% to 82%, mean 65 +/- 12%, compared with control (n=4). Histamine release to HRF/TCTP was increased only slightly in two experiments. SHIP-1 knockdown in basophils ranged from 34% to 69%, mean 51.8 +/- 7% (n=4). Histamine release to HRF/TCTP in these basophils was dependent on the amount of SHIP knockdown. Mast cells and basophils derived from CD34+ precursor cells represent suitable models for transfection studies. Reducing SHIP-1 protein in cultured mast cells and in cultured basophils increases releasability of the cells.

Induced loss of Syk in human basophils by non-IgE-dependent stimuli

In the general population, Syk expression in human basophils is highly variable and correlates well with the IgE-mediated responsiveness of these cells. Previous studies established that IgE-mediated stimulation results in loss of Syk expression. The current studies investigated whether stimulation through other receptors results in loss of Syk. Two classes of stimulation were examined, those that operate through the kinase Syk and those that operate through a GTP-binding protein. These studies demonstrated that aggregation of leukocyte Ig-like receptor LILRA-2 resulted in phosphorylation of Syk and c-Cbl, was inhibited by a third generation Syk inhibitor with an expected IC(50), and induced histamine release in strict proportion to release induced by anti-IgE Ab. Stimulation of LILRA-2 for 18 h resulted in modest loss of Syk that correlated with the more profound loss of Syk induced by anti-IgE Ab. Human recombinant histamine-releasing factor has also recently been shown to induce Syk phosphorylation and in the current studies has also been shown to induce loss of Syk in 18-h cultures. fMLP stimulation for 18 h was also found to induce modest loss of Syk. fMLP induced phosphorylation of c-Cbl that was sustained for at least 45 min. Phosphorylation of c-Cbl was inhibited by a Syk kinase inhibitor but with an IC(50) that was not consistent with Syk activity, suggesting another kinase was responsible for Cbl phosphorylation following fMLP. These studies demonstrate that it is possible to induce the loss of Syk expression in human basophils by a non-IgE-dependent mechanism and even by a mechanism that does directly involve Syk in the reaction complex.

A comparison of inflammatory mediators released by basophils of asthmatic and control subjects in response to high-affinity IgE receptor aggregation

BACKGROUND

In human blood basophils, cross-linking the high-affinity IgE receptor Fc epsilonRI with multivalent antigen activates a signaling pathway leading to secretion of inflammatory mediators and cytokine production. Basophils are known to play an important role in the pathogenesis of asthma but there has been no comprehensive examination of the effectors these cells produce. Here a study of the transcription and release of a selection of chemokines and cytokines from basophils was undertaken.

METHODS

A Cartesian antibody array provided an effective method of assaying for multiple cytokines and chemokines simultaneously. Results were verified by RT-PCR and ELISA assays. This allowed the comparison of freshly prepared peripheral blood basophil responses to cross-linking of the high-affinity IgE receptor, with and without preincubation with IL-3.

RESULTS

Evidence that human blood basophils produce the chemokines MIP-5, eotaxin and GM-CSF was provided by antibody array and RT-PCR analyses. Preincubation with IL-3 enhanced the expression and release of IL-13, IL-8 and mRNA transcripts encoding MIP-5 and GATA2 in basophils from both asthmatic and control subjects. Leptin mRNA transcription, storage and release in basophils are described for the first time.

CONCLUSIONS

Surveying cytokine and chemokines stored and released by peripheral blood basophils shows that asthmatic and control subjects share similar profiles even when their degranulation responses are distinct. Evidence is provided for the production of leptin, GM-CSF, eotaxin and MIP-5 by peripheral blood basophils. IL-3 preincubation enhances the production and release of IL-8 upon IgE receptor cross-linking.

Histamine release from the basophils of control and asthmatic subjects and a comparison of gene expression between "releaser" and "nonreleaser" basophils

Most human blood basophils respond to FcepsilonRI cross-linking by releasing histamine and other inflammatory mediators. Basophils that do not degranulate after anti-IgE challenge, known as "nonreleaser" basophils, characteristically have no or barely detectable levels of the Syk tyrosine kinase. The true incidence of the nonreleaser phenotype, its relationship (if any) to allergic asthma, and its molecular mechanism are not well understood. In this study, we report statistical analyses of degranulation assays performed in 68 control and 61 asthmatic subjects that establish higher basal and anti-IgE-stimulated basophil degranulation among the asthmatics. Remarkably, 28% of the control group and 13% of the asthmatic group were nonreleasers for all or part of our 4-year long study and cycling between the releaser and nonreleaser phenotypes occurred at least once in blood basophils from 8 (of 8) asthmatic and 16 (of 23) control donors. Microarray analysis showed that basal gene expression was generally lower in nonreleaser than releaser basophils. In releaser cells, FcepsilonRI cross-linking up-regulated >200 genes, including genes encoding receptors (the FcepsilonRI alpha and beta subunits, the histamine 4 receptor, the chemokine (C-C motif) receptor 1), signaling proteins (Lyn), chemokines (IL-8, RANTES, MIP-1alpha, and MIP-1beta) and transcription factors (early growth response-1, early growth response-3, and AP-1). FcepsilonRI cross-linking induced fewer, and quite distinct, transcriptional responses in nonreleaser cells. We conclude that "nonreleaser" and "cycler" basophils represent a distinct and reversible natural phenotype. Although histamine is more readily released from basophils isolated from asthmatics than controls, the presence of nonreleaser basophils does not rule out the diagnosis of asthma.

Histamine releasibility and expression of Lyn and Syk kinases in Indian subjects and role of less potent IL-3 in non-releaser basophils

BACKGROUND

Allergen-mediated activation of the IgE signal pathway in basophils and mast cells leads to release of mediators in-vitro and in-vivo systems. However, basophils from 10% to 20% of the population do not release histamine and other mediators on activation of the IgE signal transduction pathway and this has been attributed to the absence of tyrosine kinases Lyn and Syk. Interestingly, when these non-releaser basophils are incubated with the IL-3, it leads to the recovery of the histamine releasibility.

OBJECTIVE

To investigate histamine releasibility in the Indian population and to evaluate the role of IL-3 with reference to non-releaser phenotypes.

METHODS

Peripheral blood basophils from healthy adults were purified by density gradient centrifugation and negative immuno-selection. Histamine release assay was performed fluorometrically. Assessment of Lyn and Syk expression were carried out by flow-cytometry. SNP analysis in the IL-3 gene was carried by sequencing analysis.

RESULTS

Histamine release after ConA challenge varied greatly from 0% to 100% in Indian subjects. Eighteen percent subjects showed less than 5% histamine release (non-releasers). Flow-cytometric analysis revealed a significantly reduced expression of Lyn and Syk kinases in basophils (p<0.05). Histamine release also significantly correlated with expression of Lyn and Syk kinase (p<0.05). Non-releasers showed the presence of SNP at +79 (T-C), which leads to the one amino acid change at 8th position in the mature IL-3 from serine to proline.

CONCLUSIONS

About 18% of the Indian subjects studied showed non-releaser phenotype and also had reduced Lyn and Syk kinase expression. Non-releasers have also shown the presence of less potent isoform of IL-3/P8, which is suspected to be responsible for the non-releaser phenotype. This needs to be extended to a larger sample size and could be a potential target for the development of therapeutics for allergic patients.

New approaches to allergen immunotherapy

Allergic diseases are common problems affecting 20% to 30% of the US population. Mast cells and basophils are the primary effector cells mediating allergic inflammation through the triggering of membrane immunoglobulin E receptors (FceRI) with antigen. Allergen immunotherapy is used as one treatment for allergic disease and results in the inhibition of mast cell and basophil responses through unknown mechanisms. In this review, we examine potential mechanisms that could result in blunted human mast cell/basophil functional responses, strategies aimed at using these mechanisms to develop new immunologically based therapies, and recent findings that have broad implications toward our understanding of how mast cells/basophils become desensitized.

Relationship between spleen tyrosine kinase and phosphatidylinositol 5' phosphatase expression and secretion from human basophils in the general population

BACKGROUND

Previous studies have suggested that expression levels of spleen tyrosine kinase (syk) or phosphatidylinositol 5' phosphatase (SHIP) may explain certain extreme human basophil phenotypes.

OBJECTIVE

This study is designed to explore whether variability in syk and SHIP expression levels in the general population, alone or in concert, can account for the variability in basophil function.

METHODS

A survey of maximum responsiveness to IgE-mediated stimulation, sensitivity, and expression levels of 6 early signaling elements was performed on 36 subjects' basophils.

RESULTS

Of the 6 signaling elements, only syk and SHIP showed a correlation with maximum histamine release or cellular sensitivity. In a multiple regression, syk and SHIP together could account for 67% of population variance, although most of the variance was explained by syk expression. The pattern of expression variance syk>>SHIP1>SHIP2 approximately lyn approximately p85 approximately cbl suggested a process that primarily modulated syk levels. IL-3 is known to modulate syk levels, but we found that a 3-day incubation with IL-3 resulted in increased expression of other signaling elements to a greater degree: cbl>SHIP1>SHIP2 approximately lyn approximately p85 > or = syk, opposite the pattern in the population survey. In contrast, 18-hour stimulation with anti-IgE antibody led to marked downregulation of syk expression, modest downregulation of Fc epsilon RI expression, weak downregulation of lyn expression, and no effect on 23 other signaling elements.

CONCLUSION

Unlike studies in mice, we conclude that expression of syk is a good preconditioning predictor of basophil function in the general population.

CLINICAL IMPLICATIONS

The finding that expression of syk levels may strongly influence functional responses of basophils suggests a mechanism underlying the severity of atopic diseases.

Evaluation of basophil activation in food allergy: present and future applications

PURPOSE OF REVIEW

The diagnosis of immediate hypersensitivity relies on specific IgE and history. Because of low specificity, however, provocation challenges are often necessary. Furthermore, IgE testing does not predict features such as reaction severity; nor can it discriminate cross-reactivity from multiple sensitizations. Direct and passive basophil activation tests may address these needs. In addition, measuring basophil activation ex vivo may be useful for monitoring patients with food allergies.

RECENT FINDINGS

Several papers using basophil activation tests demonstrate comparable sensitivity and specificity to current testing for food allergy. Flow-based basophil activation tests have also been used to assess functional characteristics of patient IgE. Finally, several activation phenotypes have been identified as markers of allergic inflammation in vivo; these phenotypes appear to correspond to earlier reports of spontaneous histamine-releasing basophils in patients with active allergic inflammation.

SUMMARY

Although in their early stages, direct basophil activation tests may prove to be useful in the clinic. Indirect basophil activation studies are useful when applied to compare functional aspects of IgE. Identification of basophil activation ex vivo is a promising approach for monitoring allergic inflammation.

Are basophil histamine release and high affinity IgE receptor expression involved in asymptomatic skin sensitization?

BACKGROUND

Immunoglobulin (Ig)E-sensitized persons with positive skin prick test, but no allergy symptoms, are classified as being asymptomatic skin sensitized (AS). The allergic type 1 disease is dependant on IgE binding to the high affinity IgE-receptor (FcepsilonRI) expressed on basophils and mast cells. However, a relationship between the AS status and FcepsilonRI has not been investigated. We aimed to characterize basophils from AS by looking at histamine release (HR) (sensitivity and reactivity) and the FcepsilonRI molecule, and compare it with nonatopic (NA) or allergic (A) persons.

METHODS

Blood was obtained from NA (n = 14), grass and/or birch A persons (n = 17) and mono-sensitized grass or birch pollen AS (n = 12). The basophil sensitivity and reactivity were examined by anti-IgE triggered HR. Surface expression of FcepsilonRI and IgE were measured by flow cytometry, FcepsilonRIalpha protein was identified using a radioimmunoassay and Western blot. mRNA coding for the classic FcepsilonRIbeta-chain and the truncated form (FcepsilonRIbetaT) were determined by real-time PCR.

RESULTS

The AS group was less reactive than NA or A persons when triggered by anti-IgE and had a significant higher number of nonresponders. However, there was no difference in sensitivity among the three groups and furthermore; the groups did not vary in FcepsilonRI- and IgE-surface expression, FcepsilonRIalpha-protein level or beta/betaT ratio.

CONCLUSION

Basophils from AS persons are less reactive and include more nonresponders than basophils from NA and A persons, but do not differ regarding the FcepsilonRI molecule.

IgE- and FcepsilonRI-mediated migration of human basophils

Local accumulation of basophils at inflammatory sites is observed in experimental antigen challenge and in allergic diseases. It is not fully known what factor(s) regulates local basophil influx in tissues, and it has not been determined whether antigens belong in a panel of basophil chemoattractants. This study was designed to elucidate whether IgE- and high-affinity receptor for IgE (FcepsilonRI)-mediated stimulation can induce human basophil migration. The migration-inducing potency of an anti-FcepsilonRI alpha-chain mAb, CRA-1, was examined on human basophils. CRA-1 mAb elicited significant migration of basophils. The migration-inducing potency of this mAb was maximal at 100 ng ml-1, and CRA-1 mAb at 100 ng ml-1 attracted approximately 10% of total inoculated basophils above baseline levels after incubation for 2.5 h. Checkerboard analysis indicated that basophil migration induced by this mAb was mainly chemotactic and partially chemokinetic. An antigen, Der f 2, also induced migration of basophils from Der f-sensitive subjects. Basophils mixed with 1 ng ml-1 of CRA-1 mAb showed an exaggerated migration response to eotaxin, indicating that FcepsilonRI cross-linkage enhances basophil migration to other chemoattractants. Induction of basophil migration by IgE- and FcepsilonRI-cross-linking stimulation may, at least in part, explain the pathogenesis of local basophil accumulation clinically observed in allergic diseases such as asthma.

Loss of syk kinase during IgE-mediated stimulation of human basophils

BACKGROUND

Ongoing secretion from human basophils is a balance of activation and deactivation events. Recent studies have focused on downregulatory steps that appear to modify the presence of the activated state of various signaling molecules. We now examine downregulation regulated by mechanisms related to proteasome processing.

OBJECTIVE

To determine the long-term effects of FcepsilonRI aggregation on expression of syk kinase.

METHODS

Peripheral blood basophils were examined for changes in the expression of syk kinase after stimulation with optimal and suboptimal stimulation.

RESULTS

Stimulation results in a 20% loss of syk in 1 hour and an 80% loss of syk in longer incubations (>18 hours). Loss of syk in this time frame can occur at levels of stimulation that do not result in observable mediator release. Loss of syk occurs after stimulation with either anti-IgE antibody or antigen. Activation is shown to result in c-Cbl phosphorylation, and its association with syk and immunoblotting reveals the appearance of a ladder of syk species with molecular weights that are consistent with ubiquitylation of syk. Stimulation in the presence of a proteasome inhibitor such as lactacystin A results in the sustained presence of very high-molecular-weight ubiquitylated species, although it does not alter the presence of the syk ladder.

CONCLUSIONS

Although the loss of syk is probably too slow to account for downregulation of ongoing secretion of histamine or leukotriene C4 release, it may lead to longer-term alterations in basophil function that explain characteristics of clinical procedures like rapid drug desensitization.

IFN-alpha inhibits IL-3 priming of human basophil cytokine secretion but not leukotriene C4 and histamine release

BACKGROUND

Innate immune responses play a critical role in determining the course of acquired immunity, including that associated with allergic disease. Type I interferons, which are generated early in these reactions, are important soluble factors that prime for TH1-like activity.

OBJECTIVE

Because human basophils secrete IL-4 and IL-13 in response to both IgE-dependent and IgE-independent stimuli, we tested whether IFN-alpha, a major type I IFN, affects the production of these TH2 cytokines and/or mediator release from these cells.

METHODS

Basophils isolated from blood were treated with IFN-alpha in the presence and absence of IL-3 priming before stimulating through the IgE receptor to release histamine, leukotriene C4, and IL-4. Effects of IFN-alpha on IL-3-mediated IL-13 secretion and basophil survival were also tested. IFN-alpha receptor expression was determined by RT-PCR.

RESULTS

IFN-alpha specifically inhibited the effects IL-3 has on basophil cytokine secretion. Enhanced secretion of IL-4 resulting from IL-3 priming was significantly inhibited in cells concurrently cultured with IFN-alpha. This effect was specific for cytokine generation, because histamine and leukotriene C4 were unaffected. Furthermore, IFN-alpha blocked IL-13 secretion directly induced by IL-3. Although IFN-beta also possessed some inhibitory activity, IFN-gamma (a type II IFN) had no effect on basophil cytokine secretion. Basophils constitutively expressed mRNA for the type I IFN receptor, and IFN-alpha did not affect basophil viability with regard to inhibition of cytokine secretion.

CONCLUSIONS

These results support the belief that early innate immune responses resulting in IFN-alpha production negatively regulate allergic responses by also inhibiting priming of basophil cytokine release.

IL3 effect on basophils histamine release upon stimulation with chronic urticaria sera

BACKGROUND

Chronic urticaria is thought to be an autoimmune disorder in 35-40% of patients because of the presence of an immunoglobulin G (IgG) antibody reactive with the IgE receptor. Patients possessing this antibody are identified by the ability of serum to degranulate donor basophils to release histamine. We questioned whether priming of basophils with interleukin 3 (IL3) would facilitate identification of patients and/or alter the percentage of patients who have a positive assay.

METHODS

We incubated 37 chronic urticaria sera with basophils from donors with no urticaria with and without priming with IL3 and compared histamine release in each instance. We also preincubated basophils from a 'non-releaser' with IL3, used these cells to assay chronic urticaria sera, and assessed the contribution of complement.

RESULTS

Interleukin 3 increases the amount of histamine release by the sera which is able to activate basophils, but it does not convert negative sera into positive releasers. Interleukin 3 is able to partially reverse 'non-releaser' basophils into cells that respond to chronic urticaria sera, and complement cannot account for the augmentation seen.

CONCLUSIONS

Preincubating basophils with IL3 facilitates the identification of sera with anti-IgE receptor antibody but does not affect the percentage of sera designated as positive.

Interleukin-3, but not granulocyte-macrophage colony-stimulating factor and interleukin-5, inhibits apoptosis of human basophils through phosphatidylinositol 3-kinase: requirement of NF-kappaB-dependent and -independent pathways

Basophils are key effector cells of allergic reactions. Although proinflammatory cytokines, such as interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5, inhibit eosinophil apoptosis in vitro, little is known about basophil apoptosis, and the signalling mechanisms required for basophil survival remain undefined. To address this issue, we used a novel negative-selection system to isolate human basophils to a purity of > 95%, and evaluated apoptosis by morphology using light and transmission electron microscopy, and by annexin-V binding and propidium iodide incorporation using flow cytometry. In this study, we demonstrated that the spontaneous rate of apoptotic basophils was higher than that of eosinophils as, at 24 hr, 57.6 +/- 4.7% of basophils underwent apoptosis compared with 39.5 +/- 3.8% of eosinophils. In addition, basophil cell death was significantly inhibited when cultured with IL-3 for 48 hr (84.6 +/- 4.9% vehicle-treated cells versus 40.9 +/- 3.9% IL-3-treated cells). IL-3 also up-regulated basophil CD69 surface expression. The effects of IL-3 on apoptosis and CD69 surface expression of human basophils were completely blocked by LY294002 (LY), a potent inhibitor of phosphatidylinositol 3-kinase (PI3-K), but only partially inhibited by lactacystin, a proteasome inhibitor that prevents degradation of IkappaB and NF-kappaB translocation. These observations reveal the novel finding that IL-3 prevents basophil apoptosis through the activation of PI3-K, which is only partially NF-kappaB dependent. As basophils are active participants in allergic reactions and IL-3 is one of the abundant proinflammatory cytokines in secretions from allergic tissue, we suggest that IL-3-mediated inhibition of basophil apoptosis may exacerbate the inflammation associated with allergic disorders.

Validation of a two-color flow cytometric assay detecting in vitro basophil activation for the diagnosis of IgE-mediated natural rubber latex allergy

BACKGROUND

IgE-dependent triggering of basophils not only elicits the release of different mediators but also the up-regulation of certain markers, e.g. CD63, which can be detected by flow cytometry. We intended to investigate if flow cytometric analysis of basophil activation could be a valuable tool in the diagnosis of latex allergy, and to evaluate if the basophil activation test (BAT) could be helpful in determining the clinical significance of a positive latex IgE in individuals with negative history and negative latex skin test. Additionally we aimed to determine the role of cross-reactive carbohydrate determinants (CCDs) in causing positive latex IgE without apparent clinical significance.

METHODS

Twelve healthy controls without a history of latex hypersensitivity with a negative latex IgE and skin test (group 1), 24 individuals without a history of latex hypersensitivity with a negative latex IgE and skin test but with other inhalant allergies (group 2), and 29 latex allergic patients with a compelling history of latex allergy with a positive latex IgE and prick test (group 3) were enrolled. The diagnostic performances of the BAT were further evaluated in 13 individuals with a history of latex allergy but with negative specific IgE and/or skin test (group 4). Twenty-four individuals with positive latex IgE without apparent clinical relevance, i.e. without history of latex hypersensitivity and negative latex skin tests, were also analyzed (group 5). The putative role of CCDs causing positive latex IgE results without apparent clinical significance was evaluated by quantification of IgE for bromelain.

RESULTS

According, to the receiver operating characteristics(ROC)-generated threshold value of 17% between latex allergic patients and the pooled group of nonlatex allergic individuals, the sensitivity and specificity of the basophil activation test was 93.1% and 91.7%, respectively. In healthy controls, allergic patients without latex hypersensitivity and latex allergic patients the number of positive BATs was 0/12, 3/24 and 27/29, respectively. In the individuals with an evocative history of latex allergy but with negative latex IgE and/or skin test the BAT was positive in all 13 cases. Twenty of 24 individuals without apparent latex allergy but with positive latex IgE had a negative BAT. IgE for bromelain was positive in 1/19 sera from group 2, 1/24 sera from group 3, none of the 8 sera from group 4, but in 16/18 sera from group 5, respectively.

CONCLUSION

Flow cytometric analysis of activated basophils seems a highly sensitive and specific tool for diagnosing latex allergy. In addition, the technique might help to determine the clinical relevance of positive IgE quantification in the absence of overt latex allergy. CCDs of natural rubber latex allergens were confirmed to mimic latex sensitization.

Calreticulin is an interleukin-3-sensitive calcium-binding protein in human basophil leukocytes

BACKGROUND

IL-3 enhances basophil histamine release upon stimulation with any known secretagogue. The molecular mechanism behind this regulation is not known, although some observations suggest that IL-3 modulates the calcium part of the signal transduction mechanism. The inhibitory action of glucocorticoids on basophils can be reversed by stimulation with IL-3.

METHODS

Calcium-binding proteins in the basophil cell line KU812 were identified by two-dimensional gel electrophoresis, Calcium-overlay assay, N-terminal sequence analysis, and mass spectometry. The presence of the same proteins in purified human basophil leukocytes was established by comigration of KU812 and human basophil proteins on the two-dimensional gels. The expression of the calcium-binding proteins in the absence and presence of IL-3 and/or anti-IgE was determined by densitometric measurement of the spots on the two-dimensional gels.

RESULTS

Calreticulin was identified on the two-dimensional gel of KU812 proteins. A protein with exactly the same migration pattern was found on the gels of proteins from purified human basophils. Immunoblotting with a specific antihuman calreticulin antibody confirmed that this protein was calreticulin. Subsequent analysis showed that the expression of calreticulin in the basophils is upregulated twofold upon stimulation with rhIL-3, even in doses below those needed for enhancement of histamine release.

CONCLUSIONS

The expression of calreticulin in human basophil leukocytes is regulated by IL-3. Calreticulin is known to modulate IP3-dependent Ca2+ influx in different cell systems, and calreticulin overexpression inhibits steroid-induced transcriptional activation. Therefore, modulation of calreticulin expression may be one mechanism by which IL-3 exerts its effects on human basophils.

Multiple defects in Fc epsilon RI signaling in Syk-deficient nonreleaser basophils and IL-3-induced recovery of Syk expression and secretion

Human basophils respond to Ag-induced cross-linking of their high affinity IgE receptor, FcepsilonRI, by releasing histamine and other mediators from granules, producing IL-4 and other cytokines and, as shown in this study, by forming membrane ruffles and showing increased very late Ag-4 (VLA-4)-mediated adhesion to VCAM-1-expressing target cells. We have identified five blood donors whose basophils lack detectable levels of the FcepsilonRI-associated protein tyrosine kinase, Syk. Despite showing no obvious ultrastructural differences from normal basophils, nonreleaser basophils fail to form membrane ruffles, to show increased VLA-4-mediated adhesive activity, or to produce IL-4 in response to FcepsilonRI cross-linking. Although Syk protein levels are suppressed in basophils from all five donors, Syk mRNA is consistently present. Furthermore, culturing nonreleaser basophils for 4 days with IL-3 restores Syk protein expression and FcepsilonRI-mediated histamine release. Understanding the reversible suppression of Syk protein expression in nonreleaser basophils, and learning to replicate this property in patients with allergic inflammation could be a powerful and specific way to limit symptomatic disease.

The tyrosine kinases p53/56lyn and p72syk are differentially expressed at the protein level but not at the messenger RNA level in nonreleasing human basophils

Within the general population, individuals can be found whose basophils do not secrete after stimulation through the immunoglobulin (Ig) E receptor. In this study we compared two groups of donors, those whose basophils responded with 65+/-16% histamine release to an optimal concentration of anti-IgE antibody and those whose basophil response was not statistically different from nonstimulated release (1+/-1%). We show that these so-called nonreleasing basophils have at least 10-fold lower expression of the tyrosine kinases, lyn and syk, but normal expression of the tyrosine kinase Btk when compared with the panel of releasing basophils. Indeed, maximum histamine release correlated with expression of both syk (Spearman rank correlation coefficient [Rs] = 0.98) and lyn (Rs = 0.93). In contrast, equivalent levels of messenger RNA (mRNA) for lyn and syk kinase were found for both groups. By sequencing a critical region in the syk mRNA, our results also demonstrate that the frame shift mutation in syk leading to a premature stop codon which has been observed in other cell types is not present in nonreleasing human basophils. Our results suggest that there may be translational or post-translational regulatory mechanisms specific to the expression of two important FcepsilonRI-associated signaling elements in basophils.

The human recombinant histamine releasing factor: functional evidence that it does not bind to the IgE molecule

BACKGROUND

We have previously shown that the human recombinant histamine releasing factor (HrHRF) caused histamine release from a subset of basophils from donors with allergy, and this release seemed to be dependent on the presence of a certain type of IgE, termed IgE+. IgE molecules that did not support HrHRF-induced histamine release were termed IgE-. However, subsequently we demonstrated that HrHRF primes anti-IgE-antibody-induced histamine release from all basophils, irrespective of the type of IgE on the cell surface.

OBJECTIVE

Because these data suggested that HrHRF does not exert its biologic effects by binding to IgE, but rather that it interacted with a surface receptor on the basophil, we wanted to obtain functional evidence that HrHRF did or did not bind to the IgE molecule.

METHODS

The rat basophilic leukemia cell line (RBL-SX38), which has been transfected to express a functional human FcepsilonRI (alpha-, beta-, and gamma-chains of the receptor) in addition to the normal rat FcepsilonRI, was used. The presence of the human FcepsilonRI receptor enables these cells to be sensitized with human IgE. Cells were passively sensitized with 1000 ng/mL human IgE+ or 1000 ng/mL human IgE- for 60 minutes at 37 degrees C. Unsensitized cells served as a control. After the cells were washed, 1 x l0(5) cells were stimulated in the presence of 1 mmol/L Ca2+ with 0.1 microg/mL anti-IgE, 40 microg/mL HrHRF, or 40 microg/mL mouse recombinant HRF (MrHRF), which has 96% homology to HrHRF.

RESULTS

Mean anti-IgE-induced histamine release was 33% +/- 15%, and there was no difference between IgE+ sensitization (32% +/- 12%) and IgE- sensitization (34% +/- 18%). However, in contrast to human basophil experiments, neither HrHRF (0% +/- 0%) nor MrHRF (3% +/- 5%) caused histamine release in RBL cells sensitized with IgE+. In addition, priming the transfected RBL-SX38 cells or the parental cell line, RBL-2H3 cells, with HrHRF or MrHRF did not increase anti-IgE-induced histamine release.

CONCLUSION

The results indicate that HrHRF does not bind to IgE, either IgE+ or IgE-. Therefore it appears likely that rHRF signals through its own specific receptor, which is not expressed or functional on RBL-SX38 or RBL-2H3 cells, but which seems to be expressed on basophils of atopic and nonatopic donors.

Extracellular Signal-Regulated Kinases Regulate Leukotriene C4 Generation, But Not Histamine Release or IL-4 Production from Human Basophils

Human basophils secrete histamine and leukotriene C4 (LTC4) in response to various stimuli, such as Ag and the bacterial product, FMLP. IgE-mediated stimulation also results in IL-4 secretion. However, the mechanisms of these three classes of secretion are unknown in human basophils. The activation of extracellular signal-regulated kinases (ERKs; ERK-1 and ERK-2) during IgE- and FMLP-mediated stimulation of human basophils was examined. Following FMLP stimulation, histamine release preceded phosphorylation of ERKs, whereas phosphorylation of cytosolic phospholipase A2 (cPLA2), and arachidonic acid (AA) and LTC4 release followed phosphorylation of ERKs. The phosphorylation of ERKs was transient, decreasing to baseline levels after 15 min. PD98059 (MEK inhibitor) inhibited the phosphorylation of ERKs and cPLA2 without inhibition of several other tyrosine phosphorylation events, including phosphorylation of p38 MAPK. PD98059 also inhibited LTC4 generation (IC50 = ∼2 μM), but not histamine release. Stimulation with anti-IgE Ab resulted in the phosphorylation of ERKs, which was kinetically similar to both histamine and LTC4 release and decreased toward resting levels by 30 min. Similar to FMLP, PD98059 inhibited anti-IgE-mediated LTC4 release (IC50, ∼2 μM), with only a modest effect on histamine release and IL-4 production at higher concentrations. Taken together, these results suggest that ERKs might selectively regulate the pathway leading to LTC4 generation by phosphorylating cPLA2, but not histamine release or IL-4 production, in human basophils.

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.

Phosphorylation of cytosolic phospholipase A2 by IL-3 is associated with increased free arachidonic acid generation and leukotriene C4 release in human basophils

BACKGROUND

Human basophils secrete leukotriene C4 (LTC4) in response to various stimuli, and a short treatment with IL-3 enhances LTC4 release, although IL-3 alone does not induce LTC4 release. However, the mechanism of this priming effect of IL-3 for LTC4 generation remains unknown in human basophils.

OBJECTIVE

This study was designed to explore the mechanisms by which short treatments with IL-3 enhance stimulated secretion of LTC4, with a focus on the activation of cytosolic phospholipase A2 (cPLA2).

METHODS

The phosphorylation state of cPLA2 in human basophils was examined by its shift in electrophoretic mobility as detected by Western blotting. Free arachidonic acid (AA) and LTC4 were measured by gas chromatography-negative ion chemical ionization mass spectrometry and LTC4-specific RIA, respectively.

RESULT

Human basophils expressed cPLA2. IL-3, as well as the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate, caused a shift in the electrophoretic mobility of cPLA2, which indicated phosphorylation of cPLA2 and therefore its activation. Ionomycin at a concentration of 0.1 microg/mL was used to induce a modest elevation of cytosolic calcium response ([Ca2+]I), no apparent cPLA2 phosphorylation, and little free AA and LTC4 generation. Pretreatment with IL-3 (1 to 10 ng/mL) markedly enhanced ionomycin (0.1 microg/mL)-mediated AA and LTC4 generation. The concentration dependence of cPLA2 phosphorylation by IL-3 and its effects on free AA and LTC4 generation were similar. The selective PKC inhibitors, bis-indolylmaleimide II and Ro-31-8220 inhibited the phorbol 12-myristate 13-acetate-mediated cPLA2 electrophoretic mobility shift, but not the IL-3-mediated shift, suggesting that the IL-3 effect is PKC independent. Both the anaphylatoxin split product of the C component C5 (C5a) and f-Met-Leu-Phe induced PKC-independent cPLA2 phosphorylation with a similar time course most notable for the absence of observable changes in cPLA2 phosphorylation before 30 seconds. These results suggested an explanation for the absence of free AA generation by C5a. When [Ca2+]I was elevated in response to C5a, there was no phosphorylation of cPLA2, and by the time cPLA2 became phosphorylated, [Ca2+]I had returned to resting levels. Treatment with IL-3 preconditioned the cPLA2 by causing its phosphorylation so that the transient [Ca2+]I response, which followed stimulation by C5a, could induce the generation of free AA and LTC4.

CONCLUSION

Taken together, these results suggest that the effect of IL-3 for free AA generation and LTC4 release might be due to induction of cPLA2 phosphorylation. The studies demonstrated a need for synchronous cPLA2 phosphorylation and elevations in [Ca2+]I.

In Vitro Regulation of FcRIα Expression on Human Basophils by IgE Antibody

In vivo studies suggested the possibility of an IgE-dependent regulation of high-affinity (FcRI) IgE receptor expression on basophils. The current studies extend these observations to in vitro cultures of human basophils. Incubation of basophils for 3 to 4 weeks resulted in a slow dissociation of IgE antibody, during which time FcRI expression decreased, as measured by flow cytometry using the anti-FcRIα monoclonal antibody, 22E7, or by measuring FcRIα mass by Western blotting of whole-cell lysates. Culture of basophils with IgE resulted in upregulation of FcRIα expression by both flow cytometry and Western blotting of whole-cell lysates. Upregulation followed a linear time course during 2 weeks of culture. The relative increase in FcRIα density depended on the starting density; with starting densities of FcRIα of 10,000 to 170,000 per basophil, the upregulation varied 20- to 1.1-fold, respectively. Upregulation occurred in high-purity basophils, was not influenced by IgG at concentrations up to 1 mg/mL, and was inhibited by dimeric IgE. Heat-inactivated IgE was less effective and the monoclonal antibody CGP51901 that prevents IgE binding to FcRIα blocked the ability of IgE to induce upregulation. The dose-response curve for IgE-induced upregulation had an effective concentration50 of 230 ng/mL. Although the receptor through which IgE induces this upregulation is not yet known, several characteristics suggest that the upregulation is mediated by IgE interacting through FcRIα itself.

In Vitro Regulation of FcRIα Expression on Human Basophils by IgE Antibody

In vivo studies suggested the possibility of an IgE-dependent regulation of high-affinity (FcRI) IgE receptor expression on basophils. The current studies extend these observations to in vitro cultures of human basophils. Incubation of basophils for 3 to 4 weeks resulted in a slow dissociation of IgE antibody, during which time FcRI expression decreased, as measured by flow cytometry using the anti-FcRIα monoclonal antibody, 22E7, or by measuring FcRIα mass by Western blotting of whole-cell lysates. Culture of basophils with IgE resulted in upregulation of FcRIα expression by both flow cytometry and Western blotting of whole-cell lysates. Upregulation followed a linear time course during 2 weeks of culture. The relative increase in FcRIα density depended on the starting density; with starting densities of FcRIα of 10,000 to 170,000 per basophil, the upregulation varied 20- to 1.1-fold, respectively. Upregulation occurred in high-purity basophils, was not influenced by IgG at concentrations up to 1 mg/mL, and was inhibited by dimeric IgE. Heat-inactivated IgE was less effective and the monoclonal antibody CGP51901 that prevents IgE binding to FcRIα blocked the ability of IgE to induce upregulation. The dose-response curve for IgE-induced upregulation had an effective concentration50 of 230 ng/mL. Although the receptor through which IgE induces this upregulation is not yet known, several characteristics suggest that the upregulation is mediated by IgE interacting through FcRIα itself.

Investigation of different recombinant isoforms of grass group-V allergens (timothy grass pollen) isolated by low-stringency cDNA hybridization--antibody binding capacity and allergenic activity

A cDNA library of timothy grass pollen was screened for homologous isoforms of major group-V allergens by low stringency hybridization with a Phl p 5 (Phleum pratense) probe. After restriction analysis of the 40 clones obtained, 17 were selected for cDNA sequencing. Of these clones, two were unrelated to group-V allergens, six showed high similarity but an incomplete open reading frame and nine had high similarity with a complete open reading frame. Comparison of deduced amino acids of ten complete cDNA clones confirmed the presence of two major isoforms, a and b. Within these two subgroups, only minor sequence variations were observed. Eight isoforms were expressed in Escherichia coli K12 and purified to homogeneity. Although the subgroups a and b could be distinguished by their molecular masses and by binding constants towards monoclonal antibodies, all isoforms turned out to be biochemically similar. Ribonuclease activity as a marker for the biological function of group-V allergens was shown to be in the same range for both subgroups. Analysis of allergenic B-cell responses towards the isoforms in 26 grass pollen allergic patients revealed that the IgE reactivities to the different isoforms were identical for each individual. IgE reactivities and allergenic activities of three isovariants and an allergen of a different group were compared in a selected group of four grass pollen allergic patients by immunoblot, histamine-release and skin-prick tests. The IgE reactivity does not necessarily mirror the allergenic activity of the single molecule, and the variability of allergenic activity between the isovariants does not, in every case, depend on the structural differences of these allergens. We conclude that group-V isoallergens in grass pollen, although they can be structurally different, induce a similar B-cell response but can show variable allergenic activity. Thus, the most allergenic isoform of each important group of allergens should be sufficient for the diagnosis of type-I allergy. Whether the isoallergenic variation has any significant influence on the outcome of immunotherapy in allergic disease still has to be elucidated.

Histamine-releasing factors

There is increasing evidence that human basophils accumulate at sites of chronic inflammation, and, in particular, in allergic asthma. Investigators have, therefore, become very interested in identifying proteins that activate these cells. Recently, the gene encoding a candidate for this function, a novel molecule, the IgE-dependent histamine-releasing factor, was cloned.