Monomeric immunoglobulin E stabilizes FcepsilonRIalpha from the human basophil cell line KU812 by protecting it from natural turnover

No difference in human mast cells derived from peanut allergic versus non-allergic subjects

INTRODUCTION

Mast cells are the primary effector cells of allergy. This study aimed at characterizing human peripheral blood-derived mast cells (PBdMC) from peanut allergic and non-allergic subjects by investigating whether the molecular and stimulus-response profile of PBdMC discriminate between peanut allergic and healthy individuals.

METHODS

PBdMC were generated from eight peanut allergic and 10 non-allergic subjects. The molecular profile (cell surface receptor expression) was assessed using flow cytometry. The stimulus-response profile (histamine release induced by secretagogues, secretion of cytokines/chemokines and changes in miRNA expression following anti-IgE activation) was carried out with histamine release test, luminex multiplex assay and miRNA arrays.

RESULTS

Expression of activating receptors (FcϵRI, CD48, CD88, CD117, and C3aR) on PBdMC was not different among peanut allergic and non-allergic subjects. Likewise, inhibitory receptors (CD32, CD200R, CD300a, and siglec-8) displayed comparable levels of expression. Both groups of PBdMC were unresponsive to substance P, compound 48/80 and C5a but released comparable levels of histamine when stimulated with anti-IgE and C3a. Interestingly, among the secreted cytokines/chemokines (IL-8, IL-10, IL-13, IL-23, IL-31, IL-37, MCP-1, VEGF, GM-CSF) PBdMC from peanut allergic subjects showed a different secretion pattern of IL-31 compared to non-allergic subjects. Investigating miRNA expression from resting or activated PBdMC revealed no significantly difference between peanut allergic and non-allergic subjects.

CONCLUSION

The molecular and stimulus-response profile revealed that PBdMC from peanut allergic subjects differently express IL-31 compared to non-allergic subjects. However, since only one altered parameter was found among 893 investigated, it is still questionable if the pathophysiological mechanisms of peanut allergy are revealed in PBdMC.

Endosomal trafficking of the ligated FcvarepsilonRI receptor

In addition to initiating signaling cascades leading to mast cell mediator release, aggregation of the high affinity IgE receptor (FcvarepsilonRI) leads to rapid internalization of the cross-linked receptor. However, little is known about the trafficking of the internalized FcvarepsilonRI. Here we demonstrate that in RBL-2H3 cells, aggregated FcvarepsilonRI appears in the early endosomal antigen 1 (EEA1(+)) domains of the early endosomes within 15min after ligation. Minimal co-localization of FcvarepsilonRI with Rab5 was observed by 30min, followed by its appearance in the Rab7(+) late endosomes and lysosomes at later time points. During endosomal sorting, FcvarepsilonRIalpha and gamma subunits remain associated. In Syk-deficient RBL-2H3 cells, the rate of transport to lysosomes is markedly increased. Taken together, our data demonstrate time-dependent sorting of aggregated FcvarepsilonRI within the endosomal-lysosomal network, and that Syk may play an essential role in regulating the trafficking and retention of FcvarepsilonRI in endosomes.

Immunoglobulin E: role in asthma and allergic disease: lessons from the clinic

The role of immunoglobulin E (IgE) in allergic asthmatic disease is well established. Allergen-specific IgE binds to its cognate receptors, thus triggering a series of cellular events. These events include presentation of antigen by dendritic cells and the degranulation of mast cells and basophils to release numerous factors that play an integral part in potentiating the disease symptoms. Studies in the mouse indicate that a reduction in IgE levels could lead to significant attenuation of the allergic inflammatory response associated with diseases such as asthma, making IgE a target for the development of new therapeutic agents. Omalizumab (Xolair), a recombinant humanised monoclonal anti-IgE antibody that blocks the interaction of IgE with its receptors, is the first anti-IgE agent to undergo clinical development. Several clinical studies have been performed in adults and children with moderate-to-severe allergic asthma to evaluate the efficacy and safety of this agent, but which have also enabled an insight into the role of IgE in human disease. IgE plays a significant role in a number of allergic conditions including allergic rhinitis and allergies to various substances. Recent data suggests that local IgE production may occur in mucosal tissues and that locally significant concentrations of IgE, not reflected by serum IgE concentrations, indicate that it may play a role in non-atopic as well as atopic disease.

The high-affinity immunoglobulin-E receptor (FcepsilonRI) is endocytosed by an AP-2/clathrin-independent, dynamin-dependent mechanism

Aggregation of the high-affinity immunoglobulin E (IgE) receptor (FcepsilonRI), expressed on mast cells and basophils, initiates the immediate hypersensitivity reaction. Aggregated FcepsilonRI has been reported to rapidly migrate to lipid rafts in RBL-2H3 cells. We confirmed that aggregated FcepsilonRI is found in the lipid raft fractions of cellular lysates. Furthermore, we show that the cross-linked FcepsilonRI remains associated with detergent-resistant structures upon internalization. Previous morphological studies have reported that aggregated FepsiloncRI is endocytosed via clathrin-coated pits, which in general are not lipid raft associated. To address this apparent discrepancy, we employed siRNA to suppress expression of components of the clathrin-mediated internalization machinery, namely, clathrin heavy chain, and the AP-2 (alpha-adaptin or mu2-subunit). Transferrin receptor (TfR) is endocytosed by a clathrin-mediated process and, as expected, each transfected siRNA caused a two to threefold elevation of TfR surface expression and almost completely inhibited its endocytosis. In contrast, there was no effect on surface expression levels of FcepsilonRI nor on the endocytosis of the dinitrophenyl-human serum albumin (DNP-HSA)/IgE/FcepsilonRI complex. On the contrary, internalization of DNP-HSA/IgE/FcepsilonRI was inhibited by overexpression of a dominant-negative dynamin mutant. We conclude that internalization of cross-linked FcRI does not require the AP-2/clathrin complex but is dynamin-dependent and may be lipid raft mediated.

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.

A high-affinity natural autoantibody from human cord blood defines a physiologically relevant epitope on the FcepsilonRIalpha

Natural Abs represent the indigenous immune repertoire and are thus present at birth and persist throughout life. Previously, human autoantibodies to the alpha domain of the high-affinity IgE receptor (FcepsilonRIalpha) have been isolated from Ab libraries derived from normal donors and patients with chronic urticaria. To investigate whether these anti-FcepsilonRIalpha Abs are present in the germline repertoire, we constructed a phage Fab display library from human cord blood, which represents the naive immune repertoire before exposure to exogenous Ags. All isolated clones specific to the FcepsilonRIalpha had the same sequence. This single IgM Ab, named CBMalpha8, was strictly in germline configuration and had high affinity and functional in vitro anaphylactogenic activity. Inhibition experiments indicated an overlapping epitope on the FcepsilonRIalpha recognized by both CBMalpha8 and the previously isolated anti-FcepsilonRIalpha Abs from autoimmune and healthy donors. This common epitope on FcepsilonRIalpha coincides with the binding site for IgE. Affinity measurements demonstrated the presence of Abs showing CBMalpha8-like specificity, but with a significantly lower affinity in i.v. Ig, a therapeutic multidonor IgG preparation. We propose a hypothesis of escape mutants, whereby the resulting lower affinity IgG anti-FcepsilonRIalpha Abs are rendered less likely to compete with IgE for binding to FcepsilonRIalpha.

Interleukin-18 primes human basophilic KU812 cells for higher leukotriene synthesis

The human basophilic cell line KU812 that is an established tool for studying the function of human basophils, is differentiated into mature basophils by interleukin (IL-3) or other agents. However, whether leukotrienes (LTs)-synthesis is affected by cytokines in KU812 cells remains unknown. KU812 cells were incubated with IL-3, IL-4, IL-6, IL-13 or IL-18 for up to 14 days. The A23187 stimulated- and IgE cross-linked-synthesis of LTC(4) and LTB(4) were measured using an enzyme immunoassay (EIA). The expression of messenger RNA (mRNA) for LT-synthesizing enzymes was examined by reverse transcriptase polymerase chain reaction (RT-PCR), and the expression of 5-lipoxygenase (5-LO) was examined by immunostaining. Incubation with IL-3 (10 ng/ml) and IL-18 (10 ng/ml) induced the expression of 5-LO. A23187stimulated LT-synthesis and IgE cross-linked LT-synthesis were enhanced after incubation with IL-3 or IL-18. These results indicated that IL-3 and IL-18 primed human basophils for higher LT-synthesis. Thus, both IL-3 and IL-18 might be important factors for regulating LT-synthesis during the differentiation of human basophils.

Lysis with Saponin improves detection of the response through CD203c and CD63 in the basophil activation test after crosslinking of the high affinity IgE receptor FcepsilonRI

BACKGROUND

The basophil activation test (BAT), in which translocation of markers to the surface of blood basophils is measured in response to allergen by flow cytometry, is a rapid assay that is gaining popularity. Two markers are currently being evaluated for the BAT; CD63 and the lineage-specific CD203c. In a recent report, detection of CD203c after lysis with Saponin was shown to be superior to detection of CD63 after lysis with formic acid. We wanted to compare a) lysis with formic acid and lysis with Saponin, b) the response through CD203c and CD63, and c) the definition 10% activated cells above background with the probability binning metric T(chi) > 4, on sets of data generated with blood basophils stimulated with varying concentrations of anti-FcepsilonRI antibody.

METHODS

Blood from volunteers was incubated with serial logarithmic dilutions of anti-FcepsilonRI and subsequently with antibodies to CD203c PE and CD63 FITC. Sets of samples set up in parallel were lysed with either Saponin based Whole Blood Lysing reagent or with formic acid based Immunoprep/Q-prep. Samples were acquired on a FACS Calibur, but were compensated and analysed offline. Responders were defined as persons who had 10% or more activated basophils above background, or a T(chi) > 4, for two consecutive dilutions of anti-FcepsilonRI antibody.

RESULTS

More basophils (median 1164 vs. median 397) and better discrimination of upregulated CD203c and CD63 amongst responders were obtained after lysis with Saponin than after lysis with formic acid. We suggest that CD203c may be a more sensitive marker for the BAT than CD63, as 6/11 responders were found with CD203c, compared with 3/11 with CD63. Most responders (7/11) were identified with probability binning.

CONCLUSION

A combination of lysis with Saponin and the markers CD203c and CD63 computed by probability binning may be the most sensitive method of detecting activation of basophils after stimulation through FcepsilonRI.

A comparative study of the FcepsilonRI molecule on human mast cell and basophil cell lines

BACKGROUND

Mast cells and basophils express the high-affinity IgE receptor FcepsilonRI. We have analysed the human mast cell line LAD2 and four subclones of the basophil cell line KU812 in order to reveal possible differences concerning the FcepsilonRI surface regulation, anti-IgE-triggered activation, FcepsilonRIalpha protein stability and the mRNA level of FcepsilonRIalpha-, beta- and the truncated beta-chain (beta(T)), and thereby determine the utility of these cell lines in investigations of the FcepsilonRI biology.

METHODS

The surface expression of FcepsilonRI was assessed by flow cytometry, using the monoclonal antibody CRA1. The FcepsilonRI-induced cellular activation (i.e. cross-linking of FcepsilonRI) was determined by changes in the intracellular level of Ca2+, which was measured by fluorescence of Fura-2. The level of the FcepsilonRIalpha protein was determined by a Western blot technique and by a radioimmunoassay. The mRNA level of FcepsilonRIalpha, beta- and beta(T)-chain was analysed using real-time PCR.

RESULTS

Two KU812 subclones and especially LAD2 had FcepsilonRI surface expression which was capable of inducing cellular activation. Both the FcepsilonRI expression and stability of the FcepsilonRIalpha protein were increased when IgE was present. All the cell lines expressed mRNA of FcepsilonRIalpha-, beta- and beta(T), with LAD2 tending to have the highest expression. However, a determination of the beta/beta(T) ratio demonstrated no difference between any of the cell clones.

CONCLUSION

These cell lines are important tools in the investigation of both the FcepsilonRI molecule and the effects induced by its activation.

Human dendritic cell 1 and dendritic cell 2 subsets express FcepsilonRI: correlation with serum IgE and allergic asthma

BACKGROUND

Type 1 dendritic cells (DC1) express the high-affinity IgE receptor (FcepsilonRI); however, the regulation of FcepsilonRI expression by DCs is not well understood. Type 2 DC (DC2) expression of FcepsilonRI has not been demonstrated.

OBJECTIVE

We hypothesized that DC2 cellsalso express FcepsilonRI and that expression of FcepsilonRI by the DC1 and DC2 subsets correlates with serum IgE and allergic asthma disease status.

METHODS

To test these hypotheses, we quantitated FcepsilonRI alpha chain expression by the peripheral blood precursor DC1 (pDC1) and pDC2 subsets by using flow cytometry.

RESULTS

FcepsilonRI was expressed by the pDC1 and pDC2 subsets, as well as tissue DCs from tonsils. Relative FcepsilonRI expression by basophil, pDC1, and pDC2 subsets was 12:6.5:1, respectively. In both pDC subsets, FcepsilonRI expression was significantly greater in allergic asthmatic subjects than in nonatopic control subjects. pDC1 and pDC2 expression of FcepsilonRI was highly correlated to serum IgE concentration. The pDC1, pDC2, and basophil subsets demonstrated a similar magnitude of increase in FcepsilonRI expression relative to changes in serum IgE.

CONCLUSIONS

FcepsilonRI expression is characteristic of both the DC1 and DC2 subsets. Furthermore, FcepsilonRI expression by these cells is highly correlated to serum IgE and to basophil FcepsilonRI expression and is greater in subjects with allergic asthma. These data support the concept that novel therapeutic approaches directly targeted at FcepsilonRI expression would affect both the sensitization and the effector phases of the allergen-specific immune response.