Natural anti-FcεRIα autoantibodies may interfere with diagnostic tests for autoimmune urticaria

IgG autoantibodies against the alpha-chain of the high affinity IgE receptor are claimed to play a pathogenetic role in autoimmune urticaria. The best methods for detection of functional autoantibodies are currently the autologous serum skin test and the basophil histamine release assay. A simplified and feasible screening test would facilitate the diagnosis of autoimmune urticaria. Here we offer an explanation for the difficulties in establishing a screening test for autoantibodies directed against the alpha-chain of the high affinity IgE receptor in autoimmune urticaria. Identical autoantibodies in chronic urticaria patients and healthy donors belonging to the natural autoantibody repertoire were found by sequence analysis of anti-alpha-chain autoantibodies isolated by repertoire cloning from antibody libraries. These natural autoantibodies bound to the receptor and triggered histamine release but only if IgE was previously removed from the receptor. Diagnostic assays used for detection of antibodies directed against the IgE receptor may require signal comparison with and without the artificial removal of IgE, immune complexes, and complement in order to avoid false positive or negative results. After IgE removal diagnostic tests will detect natural autoantibodies against the high affinity IgE receptor regardless of whether they are pathogenic or not.

Blood basophil numbers in chronic ordinary urticaria and healthy controls: diurnal variation, influence of loratadine and prednisolone and relationship to disease activity

BACKGROUND

The basopenia of chronic urticaria relates to histamine releasing autoantibodies in the serum of patients with autoimmune urticaria. This reduction in circulating basophils may be due to active recruitment into weals. If so, it might be expected that numbers in blood would be reduced when urticaria is active and increased after treatment. The primary aim of this study was to look at diurnal variation of basophil numbers in patients with chronic ordinary urticaria (not physical or vasculitic) in relation to disease activity and the effect of treatment with antihistamines and corticosteroids, and to compare the results with healthy controls. A secondary aim was to compare a standard manual counting method with automated basophil counts and to look at numbers of other circulating leucocytes that might be relevant to urticaria pathogenesis.

METHODS

Manual basophil counts using a toluidine blue stain and automated 5-part differentials (Coulter Gen. S) were performed at 4-hourly intervals from 08.00 to 20.00 in 10 healthy controls (six women, age 24 to 63 years) and seven chronic urticaria patients (five women, 24 to 50 years). All chronic urticaria patients had severe daily or almost daily urticaria. Only one of six chronic urticaria sera showed in vitro basophil histamine releasing activity. Counts were performed without treatment, after a week of taking loratadine 10 mg daily and after 3 days of adding prednisolone at 0.6 mg/kg/day (maximum 40 mg). Daily urticarial activity scores (UAS) were derived from weal numbers and itch, maximum 7.

RESULTS

There was no significant overall diurnal variation of basophil numbers in healthy controls or chronic urticaria patients. Mean (SE) manually counted basophil were higher in healthy controls than chronic urticaria (43.4/ microL (2.1) vs. 4.4 (0.8), P < 0.001). Basophil counts were reduced in healthy controls on steroids (19.2 (1.9), P < 0.001) but increased in chronic urticaria (8.9 (1.9), P < 0.001). Loratadine did not influence them. UAS fell on treatment (3.3 (0.4) baseline, 1.4 (0.5) on loratadine and 0.5 (0.2) on prednisolone with loratadine, P < 0.001). There was a negative linear correlation between basophil numbers and UAS in untreated chronic urticaria patients (P = 0.001, Spearman rank correlation). Manual and automated basophil counts showed poor agreement. Lymphocyte numbers were lower in chronic urticaria than healthy controls. Neutrophils increased whereas lymphocytes and eosinophils decreased in all subjects on prednisolone. They were unaffected by loratadine.

CONCLUSION

The results are consistent with the hypothesis that circulating basophils may be recruited from blood into urticarial weals during disease activity. Automated counts are not suitable for assessing basophil numbers in chronic urticaria. The relevance of reduced lymphocyte numbers in chronic urticaria needs to be explored.

Chronic urticaria

Chronic urticaria has a spectrum of clinical presentations and causes. About 50% of patients with "idiopathic" disease have histamine-releasing autoantibodies in their blood. The term autoimmune urticaria is increasingly being accepted for this subgroup of patients, in whom immunosuppressive therapies may be appropriate if conventional approaches to management are unsuccessful. This article reviews the classification, causes, and management of chronic urticaria in light of recent advances in the understanding of its etiology.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should have up-to-date knowledge of the classification, assessment, and management of chronic urticaria and understand where the concept of autoimmune urticaria fits into existing frameworks.

Basophils in chronic urticaria

Blood basophils are reduced in chronic urticaria and respond less well to immunologic stimuli. Active recruitment of basophils from peripheral blood into lesional skin may be important in wheal pathogenesis.

Autoimmunity in chronic urticaria and urticarial vasculitis

In contrast to acute urticaria, etiology cannot be identified in most cases of chronic urticaria. Recent evidence suggests that a subset of patients with chronic urticaria may have an autoimmune basis for their condition. The demonstration of antithyroid autoantibodies in some patients with chronic idiopathic urticaria (CIU) provides support for an association. However, the discovery of a positive skin test response to intradermal injection of autologous serum in as many as 60% of patients with CIU led to the identification of autoantibodies to IgE and the alpha-chain of the high-affinity IgE receptor, Fc epsilon RI alpha. Additional studies have demonstrated that some of these autoantibodies are capable of releasing histamine from donor basophils and mast cells. This article reviews the literature that addresses a possible autoimmune etiology in a subset of patients with CIU. Urticarial vasculitis is differentiated from chronic urticaria based on clinical features and biopsy findings of leukocytoclastic vasculitis. Most cases of urticarial vasculitis are secondary to an underlying systemic disease. The presence of autoantibodies has also been demonstrated in a subset of patients with primary urticarial vasculitis. This article briefly reviews some of this data.

NSAID intolerance in chronic idiopathic urticaria: A study of its relationship with histamine-releasing activity of patients' sera

BACKGROUND

about one fourth of patients with chronic idiopathic urticaria (CIU) experience flares of hives after taking chemically unrelated nonsteroidal anti-inflammatory drugs (NSAID). The reasons for such intolerance are still elusive.

OBJECTIVE

this study aimed to investigate NSAID intolerance in patients with CIU in view of the in vivo and in vitro histamine releasing activity of their sera.

METHODS

117 adults (M/F 41/76) with CIU underwent intradermal test with autologous serum, and the ability of their sera to induce histamine release from normal blood donors was evaluated. NSAID intolerance was ascertained by careful interview.

RESULTS

overall, 32/117 (27 %) patients reported NSAID intolerance. The prevalence on NSAID intolerance did not differ in the three subgroups: negative on both in vivo and in vitro tests (9/36; 25 %), positive or intradermal test but negative on basophil histamine release assay (16/58; 28 %), or positive on both in vivo and in vitro tests (7/23; 30 %).

CONCLUSION

in patients with CIU intolerance to NSAID does not depend on the mechanism of histamine release.

Frequency and characterization of antigen-specific IL-4- and IL-13- producing basophils and T cells in peripheral blood of healthy and asthmatic subjects

BACKGROUND

Both basophils and T cells are known to secrete IL-4 and IL-13 after activation with either nonspecific stimuli or specific antigen, but the relative contribution of these 2 cell types to overall cytokine production is unclear.

OBJECTIVES

To further characterize basophil cytokine production and compare it with that of T cells, we examined the frequency of IL-4- and IL-13-producing basophils and T cells in human PBMCs by means of flow cytometry after activation in allergic asthmatic and normal subjects.

METHODS

PBMCs obtained from whole blood after Percoll gradient were activated with specific antigen or ionomycin and fixed. PBMCs were made permeable; stained with antibodies to IgE, CD3, and either IL-4 or IL-13; and analyzed by means of flow cytometry.

RESULTS

Preformed cytokines were not detected in unactivated basophils. After ionomycin activation, 60% to 90% of basophils from both control and allergic asthmatic subjects expressed IL-4 and IL-13. Specific antigen induced cytokine expression by 10% to 20% of basophils from the asthmatic group only. After specific antigen activation, basophils accounted for 4 times more IL-4-producing cells than did T cells. IL-4 and IL-13 production at 2 hours was exclusively from basophils. After allergen activation, CD40 ligand was upregulated on a subset of peripheral blood basophils.

CONCLUSIONS

These data demonstrate that basophils are the predominant peripheral blood cells that express IL-4 and IL-13 in the first 6 hours after antigen activation and strengthen the putative role of basophils both in IgE production and in the generation of allergic inflammation.

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

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