Polymerization of actin does not regulate desensitization in human basophils

Defining Optimal Basophil Passive Sensitisation Parameters

BACKGROUND

Detecting drug-specific IgE (sIgE) is crucial for diagnosing immediate drug-induced hypersensitivity reactions. Basophil activation tests serve as a method to determine the presence of drug-sIgE, highlighting the importance of optimising the assay. Optimisation involves considering multiple factors to ensure sensitisation helps detect an antigen sIgE. The study investigates the complex factors influencing basophil responsiveness thresholds and aims to provide rules-of-thumb guidance for expected results.

METHODS

Open and occupied FcεRI receptors were analysed by flow cytometry pre- and postdissociation of surface-bound sIgE. Basophils were then sensitised with serial concentrations of penicillin (BPO)-sIgE in serum or buffer and incubated for 1, 4 and 18 h with or without D2O and/or IL-3. Basophil sensitivity was evaluated based on FcεRI receptor densities, sIgE/total IgE (tIgE) ratios, responses to BPO(21)-HSA, and D2O and/or IL-3 effects, with maximal responses determined using anti-IgE human antibodies. These optimised conditions were tested with peanut-sIgE and cat-sIgE sera.

RESULTS

Basophils from five donors were used. The FcεRI receptor expression initially averaged 155,000/cell (47,000-344,000/cell), with 35% (5%-79%) unoccupied, which postdissociation increased to 98% (82%-100%) unoccupied. Upon sensitisation, the average reloading with BPO-sIgE was 39% (33%-48%). The ED50 (a measure of cellular sensitivity) was approx. 6000 BPO-sIgE/cell, and the average maximal anti-IgE antibody response was 58% (25%-68%). A 4-h sensitisation at 4°C with IL-3 pretreatment and 70% D2O allowed the detection of BPO-sIgE/tIgE ratios as low as 0.02%-0.05% without spontaneous histamine release. Under the same conditions, responses were detected with 0.33% peanut-sIgE and 0.1% cat-sIgE ratios.

CONCLUSION

This study outlines a method to assess basophil sensitisation, emphasising the minimum sIgE/tIgE ratio needed for basophil responsiveness. It considers factors like FcεRI open/unoccupied FcεRI receptors, sIgE/tIgE ratios and the effect of D2O and IL-3. This sets a strong foundation for refining and advancing basophil activation functional assays.

Temporal Modulation of Drug Desensitization Procedures

Drug hypersensitivity reactions are an unavoidable clinical consequence of the presence of new therapeutic agents. These adverse reactions concern patients afflicted with infectious diseases (e.g., hypersensitivity to antibiotics), and with non-infectious chronic diseases, such as in cancers, diabetes or cystic fibrosis treatments, and may occur at the first drug administration or after repeated exposures. Here we revise recent key studies on the mechanisms underlying the desensitization protocols, and propose an additional temporal regulation layer that is based on the circadian control of the signaling pathway involved and on the modulation of the memory effects established by the desensitization procedures.

Optimizing drug inhibition of IgE-mediated anaphylaxis in mice

BACKGROUND

Administering allergens in increasing doses can temporarily suppress IgE-mediated allergy and anaphylaxis by desensitizing mast cells and basophils; however, allergen administration during desensitization therapy can itself induce allergic responses. Several small molecule drugs and nutraceuticals have been used clinically and experimentally to suppress these allergic responses.

OBJECTIVES

This study sought to optimize drug inhibition of IgE-mediated anaphylaxis.

METHODS

Several agents were tested individually and in combination for ability to suppress IgE-mediated anaphylaxis in conventional mice, FcεRIα-humanized mice, and reconstituted immunodeficient mice that have human mast cells and basophils. Hypothermia was the readout for anaphylaxis; therapeutic efficacy was measured by degree of inhibition of hypothermia. Serum mouse mast cell protease 1 level was used to measure extent of mast cell degranulation.

RESULTS

Histamine receptor 1 (HR1) antagonists, β-adrenergic agonists, and a spleen tyrosine kinase (Syk) inhibitor were best at individually inhibiting IgE-mediated anaphylaxis. A Bruton's tyrosine kinase (BTK) inhibitor, administered alone, only inhibited hypothermia when FcεRI signaling was suboptimal. Combinations of these agents could completely or nearly completely inhibit IgE-mediated hypothermia in these models. Both Syk and BTK inhibition decreased mast cell degranulation, but only Syk inhibition also blocked desensitization. Many other agents that are used clinically and experimentally had little or no beneficial effect.

CONCLUSIONS

Combinations of an HR1 antagonist, a β-adrenergic agonist, and a Syk or a BTK inhibitor protect best against IgE-mediated anaphylaxis, while an HR1 antagonist plus a β-adrenergic agonist ± a BTK antagonist is optimal for inhibiting IgE-mediated anaphylaxis without suppressing desensitization.

Response of peripheral blood basophils in subjects with chronic spontaneous urticaria during treatment with omalizumab

BACKGROUND

Treatment of patients with asthma or food allergy with omalizumab results in several consistent changes in circulating basophils. The multiple basophil phenotypes observed in patients with chronic spontaneous urticaria (CSU) present some unique attributes that may not respond in a similar fashion to patients with asthma or food allergy. As part of a clinical study on the therapeutic outcomes of omalizumab treatment in CSU, the basophil compartment was examined for changes in characteristics predicted by prior studies.

OBJECTIVE

This study sought to examine the changes in basophil function and its relationship to auto-antibodies in serum during treatment with omalizumab.

METHODS

At multiple time points before and during omalizumab treatment of patients with CSU, basophil surface IgE and FcεRI expression, cellular spleen tyrosine kinase (SYK) expression, IgE-mediated histamine release (HR), and the presence of auto-antibodies in serum were determined.

RESULTS

Three basophil phenotypes were enumerated in the clinical study and used to group results in this basophil study: subjects with (1) basopenia, (2) normal basophil numbers with normal IgE-mediated HR, and (3) normal basophil numbers with poor HR. Basopenia was highly associated with the presence of auto-antibodies to unoccupied FcεRI and basophil numbers did not change during treatment. Likewise, subjects who are basopenic showed no changes in SYK expression or HR during treatment. In basophils of subjects who are nonbasopenic, increases in SYK expression and HR showed the expected inverse relationship to starting SYK and HR levels. Treatment with omalizumab resulted in similar kinetics for decreases in surface FcεRI and IgE in all 3 groups.

CONCLUSIONS

A unifying interpretation of the results revolves around the presence of auto-antibodies to FcεRI in CSU. If present, basopenia and an absence of changes in basophils during omalizumab treatment are observed. If auto-antibodies are absent, the changes in the basophil compartment are consistent with prior studies of asthma and food allergy. These group differences also are related to efficacy of the treatment for clinical outcomes, as found in the parent clinical study.

Rapid desensitization of humanized mice with anti-human FcεRIα monoclonal antibodies

BACKGROUND

Anaphylaxis is classically mediated by allergen cross-linking of IgE bound to the α chain of FcεRI, the mast cell/basophil high affinity IgE receptor. Allergen cross-linking of the IgE/FcεRI complex activates these cells, inducing release of disease-causing mediators, cytokines, and enzymes. We previously demonstrated that IgE-mediated anaphylaxis could be safely prevented in wild-type BALB/c mice by rapid desensitization with anti-mouse FcεRIα mAb.

OBJECTIVE

This study sought to use humanized mice to extend these results to humans.

METHODS

We actively immunized huFcεRIα/F709 mice, which express human (hu) instead of mouse FcεRIα and a mutant IL-4 receptor that lacks inhibitory function. We passively immunized huFcεRIα mice, as well as human cord blood-reconstituted reNSGS mice, which are immune-deficient, produce mast cell-stimulating human cytokines, and develop numerous human mast cells. For desensitization, we used anti-huFcεRIα mAbs that bind FcεRIα regardless of its association with IgE (noncompeting mAbs), and/or mAbs that compete with IgE for huFcεRIα binding (competing mAbs). Anaphylaxis was induced by intravenous injection of antigen or anti-huIgE mAb.

RESULTS

Anti-huFcεRIα mAb rapid desensitization was safer and more effective than allergen rapid desensitization and suppressed anaphylaxis more rapidly than omalizumab or ligelizumab. Rapid desensitization of naïve, IgE-sensitized huFcεRIα mice and huFcεRIα/F709 mice that were egg-allergic with anti-FcεRIα mAbs safely removed >98% of IgE from peritoneal mast cells and completely suppressed IgE-mediated anaphylaxis. Rapid desensitization of reNSGS mice with anti-FcεRIα mAbs also safely removed ∼98% of mast cell IgE and prevented IgE-mediated anaphylaxis.

CONCLUSIONS

Rapid desensitization with anti-FcεRIα mAbs may be a safe, effective, and practical way to prevent IgE-mediated anaphylaxis.

Recovery from desensitization of IgE-dependent responses in human lung mast cells

BACKGROUND

Clinical desensitization and oral food immunotherapy are therapeutic interventions that allow individuals who react adversely to an allergen (drug or food) to be made tolerant to the allergen. However, tolerance is brief, and allergen hypersensitivity can recur within days following allergen withdrawal.

OBJECTIVE

We hypothesize that the reason these treatments are temporary reflects rapid recovery of mast cells from a desensitized state. We sought to test this.

METHODS

Desensitization of IgE-mediated histamine release from human lung mast cells was explored by methods that partially replicate the pattern of treatment during clinical desensitization. Specific and non-specific desensitization and changes in surface IgE were examined following desensitization. Recovery from desensitization was also studied.

RESULTS

Desensitization of mast cell responses was readily induced with concentrations of antigen or anti-IgE that were suboptimal for secretion. There was little or no non-specific desensitization when lung mast cells were exposed to antigens. There was no loss of cell surface IgE following desensitization. Removing the desensitizing stimulus from the media following desensitization allowed the cells to recover with half-point of recovery of ~1.5 days and complete recovery after 5 days. Both the functional response and histamine content recovered within this time frame. The recovery appeared possible because both antigens and anti-IgE dissociated rapidly from cells after washing to remove excess stimulus.

CONCLUSIONS AND CLINICAL RELEVANCE

Human lung mast cells readily recover from a desensitized state following removal of desensitizing antigen. This finding provides a potential explanation for the ephemeral nature of clinical desensitization.

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.

Marked differences in the signaling requirements for expression of CD203c and CD11b versus CD63 expression and histamine release in human basophils

Many techniques are being used to examine the status of circulating human basophils including the enhanced expression of a variety of cell surface proteins. There is accumulating evidence that there are at least two compartments containing these activation marker proteins but there are only some indications for the signaling requirements for each of the compartments. This study began with published reports by other investigators who potentially dissociated CD63 expression from anaphylactic degranulation with the p38 inhibitor, SB203580, a possible falsification of a previously proposed hypothesis regarding CD63 expression. To explore the signaling requirements for CD63, a variety of pharmacological agents were used to inhibit or enhance 4 endpoints of basophil activation. First, it was found that inhibition of both histamine release and CD63 expression with SB203580 was concordant. But it was also found that this agent had no effect on increased expression of CD203c and CD11b. Actin polymerization inhibitors caused marked enhancement of CD63 expression (concordant with their effects on degranulation) with no effect on expression of CD203c and CD11b. The third generation syk inhibitor, NVP-QAB205, showed a 5-fold lower potency for inhibiting expression of CD203c and CD11b than for CD63. Finally, while desensitization of CD11b and CD203c expression occurs, it is slower than desensitization of the CD63 response. Taken together, these various observations demonstrate a marked difference in the early signaling requirements for the CD11b/CD203c compartment and CD63 degranulation and provide support for the hypothesis that CD11b and CD203c reside in a similar compartment.

Immunology in the Clinic Review Series; focus on allergies: basophils as biomarkers for assessing immune modulation

Allergen-specific immunotherapy is an effective clinical treatment for hypersensitivity to many allergens. Studies of basophils during immunotherapy have provided insight into underlying immune mechanisms and support the potential use of basophil activation as a biomarker of clinical outcomes. This review examines the evidence for different pathways of basophil modulation associated with various forms of immunotherapy. Better understanding the molecular mechanisms of basophil activation and desensitization and the relationship between suppression of these effector cells to clinical outcomes holds promise for further development and improvement in potential therapies for allergic diseases.

Inhibition of IgE-mediated secretion from human basophils with a highly selective Bruton's tyrosine kinase, Btk, inhibitor

The study of receptor-mediated signaling in human basophils is often limited by the availability of selective pharmacological agents. The early signaling reaction mediated by FcεRI aggregation is thought to require the activity of Bruton's tyrosine kinase (btk), an enzyme that has been identified as important in B cells signaling because mutations lead to X-linked agammaglobulinemia. This study uses the btk selective irreversible inhibitor, PCI-32765, to explore the role of btk in a variety of functions associated with the activation of human basophils. Nine endpoints of basophil activation were examined: induced cell surface expression of CD63, CD203c, CD11b; induced secretion of histamine, LTC4, IL-4 and IL-13; the cytosolic calcium response; and the induced loss of syk kinase. Four stimuli were examined; anti-IgE antibody, formyl-met-leu-phe (FMLP), C5a and IL-3. For stimulation with anti-IgE, PCI-32765 inhibited CD63, histamine, LTC4 and IL-4 secretion with an IC50 of 3-6 nM (with 100% inhibition at 50 nM) and it inhibited CD203c and CD11b and the cytosolic calcium response with and IC50 of 30-40 nM. Fifty percent occupancy of btk with PCI-32765 occurred at ~10nM. Consistent with btk functioning downstream or in parallel to syk activation, PCI-32765 did not inhibit the loss of syk induced by anti-IgE in overnight cultures. Finally, PCI-32765 did not significantly inhibit basophil activation by FMLP or C5a and did not inhibit IL-13 release induced by IL-3. These results suggest that btk is specifically required for IgE-mediated activation of human basophils.