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 FcεRI in basophils differs among subjects. This observation raised the possibility that the stoichiometry of FcRβ:FcεRIα is not fixed to 1:1 and might be modifiable during changes in the basophil environment.

Objective

To determine if treatment with omalizumab results in increases in syk expression, anti-IgE-mediated histamine release and disproportionately alters the relative presence of FcRβ and FcεRIα.

Method

Syk, FcεRIα, and FcRβ 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 FMLP, a response that also increases in the presence of IL-3. There was a 60% decrease in the FcRβ:FcεRIα 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 by an IgE-dependent mechanism and that the ratio of FcεRI alpha and beta subunits in basophils is influenced by factors extrinsic to the cell.

BACKGROUND

Omalizumab treatment suppresses FcεRI expression faster on blood basophils than skin mast cells.

OBJECTIVE

We utilized omalizumab to elucidate the relative contributions of basophil versus mast cell FcεRI activation in a nasal allergen challenge (NAC) model.

METHODS

Eighteen cat-allergic subjects were enrolled in a 3.5-month, double-blind, randomized (3.5:1), placebo-controlled trial of omalizumab using standard dosing. At baseline, subjects underwent NAC with lavage for PGD2 measurement, skin prick test titration (SPTT), and blood sampling for basophil histamine release (BHR) and basophil IgE/FcεRI measurements. Basophil studies were repeated at day 3 and then weekly until cat allergen-induced BHR was <20% of baseline or until day 45. Baseline visit procedures were repeated after the BHR reduction (mid-study NAC) and at the treatment period’s completion (final NAC).

RESULTS

Subjects treated with omalizumab who completed all NACs (n=12) demonstrated significant mean reduction in BHR to an optimal dose of cat allergen by mid-study NAC as compared to baseline (74% decrease, p=0.001). In addition, these subjects demonstrated significant decreases in mean combined nasal symptom scores (50% decrease, p=0.007) and total sneeze counts (59% decrease, p=0.01) by mid-study NAC relative to baseline NAC. In contrast, measures of mast cell response (SPTT and nasal lavage PGD2) were only significantly reduced by the final NAC. Subjects on placebo (n=4) did not experience a shift in basophil, NAC symptom, or mast cell measures.

CONCLUSIONS

Reduction in nasal symptom scores occurred when the basophil, but not mast cell, response was reduced on omalizumab, implicating a role for basophils in the acute NAC response.

Background

Basophil activation has been implicated in the pathogenesis of aspirin exacerbated respiratory disease. However, a comprehensive analysis of basophil responses to aspirin in terms of mediator release, cytokine secretion and increased expression of surface activation markers has not been performed.

Objective

To study the in vitro effects of aspirin on the concurrent release of histamine, leukotriene C4 and IL-4 from human basophils and to also evaluate changes in surface activation markers (CD63, CD69 and CD203c) expressed by these cells.

Methods

Basophil-enriched cell suspensions from 10 patients with aspirin exacerbated respiratory disease and 10 healthy volunteers were incubated with lysine-aspirin for up to 3 hours. Cells were analysed for expression of CD63, CD69 and CD203c using flow cytometry. Cell-free supernatants were evaluated for histamine, and leukotriene C4 release and for IL-4 secretion.

Results

Aspirin-induced expression of CD63, CD69 and CD203c yielded 30%, 80% and 70% sensitivity, respectively, but with poor specificity. There was no significant difference in leukotriene C4 synthesis between groups. None of the patients with aspirin exacerbated respiratory disease (or controls) released IL-4 in response to aspirin. A higher dose of 5 mg/ml aspirin mediated non-specific effects on basophils.

Conclusion

Basophil responses to in vitro aspirin challenge are poor indicators of clinical sensitivity. Aspirin activates some basophils by means of mechanisms which differ from the classical IgE mediated pathway. Our study also shows that the use of 27 mM of aspirin (5 mg/ml) used by previous investigators causes nonspecific basophil activation, thereby eliminating its usefulness in a cell based diagnostic test for AERD. Evaluation of in vitro basophil activation has low clinical value in identifying aspirin- induced respiratory reactions

Recently, signaling changes in the FcεRI pathway involving inositol lipid phosphatases have been identified in the basophils of chronic idiopathic urticaria (CIU) subjects. Based on the profile of basophil FcεRI-mediated histamine degranulation, we have segregated CIU subjects into two groups, CIU Responder (CIU R) or CIU Nonresponder (CIU NR). In the present study, we compared expression of SHIP-1, SHIP-2, and Syk protein to histamine release (HR) from mast cells (MC) cultured from the peripheral blood of CIU R, CIU NR, and normal subjects. The MC of CIU R donors contained significantly increased Syk and decreased SHIP-2 as compared to CIU NR (Syk: p=0.038: SHIP-2: p=0.038) and normals (Syk: p=0.042: SHIP-2: p=0.027). Spontaneous HR from CIU donors was increased two-fold compared to normals (p=0.04). In summary, our results suggest a possible predilection for urticarial MC to spontaneously degranulate upon IgE sensitization contributing to the increased pruritis associated with CIU.

Chronic urticaria is a common skin disease without a clear etiology in the vast majority of cases. The similarity of symptoms and lesion pathology to allergen-induced skin reactions supports the idea that skin mast cell and blood basophil IgE receptor activation is involved, however, no exogenous allergen trigger has been identified. The presence of serum IgG autoantibodies targeting IgE or the IgE receptor in ∼40 % of CIU cases supports the theory of an autoimmune basis for the disease. However, issues remain with the assays to detect autoantibodies amongst other serum factors, the relationship of autoantibodies to CIU disease activity, and the occurrence of autoantibodies in healthy subjects. Other studies have identified altered IgE receptor degranulation that reverts in disease remission and is accompanied by changes in signaling molecule expression and function in mast cells and basophils in active CIU subjects. The arrival of therapies targeting IgE and the IgE receptor pathway elements has potential use in CIU.

Food allergy is a serious and potentially life-threatening problem for an estimated 6% of children and 3.7% of adults. This review examines the diagnostic process that begins with a patient's history and physical examination. If the suspicion of IgE-mediated food allergy is compelling based on the history, skin and serology tests are routinely performed to provide confirmation for the presence of food-specific IgE antibody. In selected cases, a provocation challenge may be required as a definitive or gold standard reference test for confirmation of IgE mediated reactions to food. Variables that influence the accuracy of each of the diagnostic algorithm phases are discussed. The clinical significance of food allergen-specific IgE antibody cross-reactivity and IgE antibody epitope mapping of food allergens is overviewed. The advantages and limitations of the various diagnostic procedures are examined with an emphasis on future trends in technology and reagents.