IgG anti-IgE from atopic dermatitis induces mediator release from basophils and mast cells

In vitro basophil histamine-releasing activity of circulating IgG1 and IgG4 autoanti-IgE antibodies from asthma patients and the demonstration that anti-IgE modulates allergen-induced basophil activation

In this study we have examined the relationship between the in vitro basophil histamine-releasing activity of human IgG anti-IgE, isolated as euglobulin fractions from sera of asthmatic patients, and its IgG1/IgG4 subclass distribution. In particular, we have investigated whether IgG anti-IgE modulates allergen-induced basophil activation. The study has revealed that only a small proportion of IgG anti-IgE samples triggered histamine release from basophils of an asthmatic individual (4/21; 19%), a hay fever sufferer (4/10; 40%) and a healthy person (7/21; 33%). The basophil histamine-releasing activity of IgG anti-IgE did not seem to be determined by the IgG1/IgG4 subclass composition of the IgG anti-IgE preparation used. Furthermore, we have demonstrated that autoanti-IgE antibodies modulate allergen-induced basophil histamine release. The three modulatory effects exerted by IgG anti-IgE antibodies on allergen-triggered basophil activation (i.e. additive, synergistic and blocking) were not dependent on the subclass nature of IgG anti-IgE or the use of histamine-releasing anti-IgE preparations. Our data suggest that IgG anti-IgE antibodies in asthma patients may consist of two functionally distinct subpopulations: those which up-regulate (pro-allergic) and those which down-regulate (anti-allergic) the allergic release of mediators from mast cells and basophils.

Circulating levels of IgG1 and IgG4 anti-IgE antibodies and asthma severity

In this paper, we have determined the levels of IgG1 and IgG4 anti-IgE in the sera of 66 asthma patients suffering from mild (n = 24), moderate (n = 23), or severe (n = 19) symptoms, and 20 nonatopic, healthy subjects. The study has revealed that although asthma patients have significantly elevated levels of IgG1 and IgG4 anti-IgE antibodies, the concentration of these autoantibodies is not related to the severity of asthma. This conclusion may be related to the known heterogeneity of autoanti-IgE antibodies in terms of their ability to trigger basophil histamine release.

Mechanisms of activation of human mast cells and basophils by general anesthetic drugs

A study was performed about the effects of increasing concentrations of muscle relaxants (suxamethonium, d-tubocurarine, vecuronium, and atracurium), hypnotics (propofol, ketamine, and thiopental), opioids (morphine, buprenorphine, and fentanyl), and benzodiazepines (diazepam, flunitrazepam, and midazolam) on the release of preformed (histamine and tryptase) and de novo synthesized (prostaglandin D2: PGD2 and peptide-leukotriene C4: LTC4) chemical mediators from human basophils and mast cells isolated from skin (HSMC), lung parenchyma (HLMC) and heart tissue (HHMC). None of the drugs tested induced the release of histamine or LTC4 from basophils of normal donors. Suxamethonium did not induce mediator release from any type of human mast cell tested. Only the highest concentration of d-tubocurarine used caused histamine release from HSMC and HLMC. Atracurium, more than vecuronium, induced concentration-dependent histamine release from HSMC and HLMC. Propofol induced a concentration-dependent histamine release from HLMC, but not from HHMC. Only the highest concentrations of ketamine and thiopental used caused a significant release of histamine from HLMC. The muscle relaxants and hypnotics examined did not induce any de novo synthesis of PGD2 or LTC4 in mast cells. Morphine only induced histamine and tryptase release from HSMC, but not the de novo synthesis of PGD2. In contrast, buprenorphine caused histamine and tryptase release from HLMC, and not from HSMC, whilst it also induced de novo synthesis of PGD2 and LTC4 in HLMC. Fentanyl did not give any histamine and tryptase release from mast cells. Diazepam and flunitrazepam only induced a small release of histamine from mast cells, whereas midazolam caused the release of histamine from HLMC. The biochemical pathways underlying the release of mediators from human mast cells induced by drugs used during general anaesthesia are different from those underlying the immune release of histamine. From the results obtained with the in vitro model described here, it is clear that new drugs promising for the anesthesiologic arena should be tested in vitro before their potential histamine-releasing activity is experienced in vivo.

The detection of autoantibodies to IgE in plasma of individuals infected with hookworm (Necator americanus) and the demonstration of a predominant IgG1 anti-IgE autoantibody response

In this study we have demonstrated significantly elevated levels of circulating IgG autoanti-IgE antibody in hookworm infected individuals from Kebasob village on Karkar Island, Papua New Guinea. Although anti-IgE activity was demonstrable in IgG1, IgG3 and IgG4, IgG1 was by far the most important subclass of IgG anti-IgE in terms of frequency of detection (34/39; 87.2%) and magnitude of increase (P = 0.0000); with IgG3 (16/39; 41.0%) and IgG4 (15/39; 38.5%) antibodies being considerably less prevalent. Plasma levels of IgG1 anti-IgE (P = 0.0019) and IgG3 anti-IgE (P = 0.0034) showed significant correlations with total IgE concentrations, but not with IgE specific to excretory-secretory worm products; thus suggesting that anti-IgE synthesis is more related to polyclonal hyper IgE production than to antigen-specific IgE stimulation. No correlation was seen between IgG subclass anti-IgE levels and faecal egg counts or worm burden. Given that our data failed to show a negative or a positive correlation between anti-IgE and the degree of infection with hookworm, it is tempting to speculate that the main role of autoanti-IgE is to provide the host with protection against immune complex- and IgE-mediated hypersensitivity reactions to parasitic antigens.

A specific feedback by anti-IgE autoantibodies on the cytokine network in allergy

During recent years we have shown that anti-IgE antibodies can have different biological functions. Depending on their epitope specificity they can be anaphylactogenic or not, they interfere with IgE binding to its receptor or not, and they enhance or inhibit IgE synthesis. Therefore we propose a theoretical model implying that anti-IgE autoantibodies are specific feed back molecules that neutralize IgE induced by the cytokine network. In the normal individual this system would be beneficial, where as the atopic individual, due to differences in its B cell repertoire, will produce the wrong type of anti-IgE antibody. The wrong type of anti-IgE antibody may even aggravate the disease as some of these autoantibodies may induce IgE synthesis or trigger effector cells that in turn generate a Th2 like cytokine pattern.

Detection of circulating histamine releasing autoantibodies with functional properties of anti-IgE in chronic urticaria

Circulating histamine releasing factor(s) have been demonstrated previously in chronic urticaria by an immediate weal-and-flare response to intradermal autologous serum injection. We have studied 25 chronic urticaria patients by in vivo skin testing with autologous sera and an in vitro histamine release assay using mixed leukocytes of healthy donors, to define the nature and functional properties of the serum factor(s). Twenty showed a weal response to autologous serum (mean +/- s.e.m., 37.3 +/- 6.8 mm3). Weal formation was confined to ultrafiltered serum fractions greater than 100 kD in nine of nine patients. There was no response in 10 healthy controls of five patients with symptomatic dermographism. Fourteen chronic urticaria sera elicited histamine release greater than 10% (mean +/- s.e.m., 44.3% +/- 6.7) above basal levels from leukocytes of at least one of seven healthy donors. This in vitro response was also confined to ultrafiltered serum fractions greater than 100 kD in seven of seven sera and was present in IgG fractions of six of seven chronic urticaria sera that showed histamine releasing activity. Functional studies indicated that this histamine releasing autoantibody had the properties of anti-IgE: chronic urticaria sera 'desensitized' basophil leukocytes to subsequent challenge with other chronic urticaria sera and to goat anti-human IgE antibody; human myeloma IgE inhibited histamine release from leukocytes in response to chronic urticaria sera; removal of surface-bound IgE by lactic acid 'stripping' reduced histamine release in response to chronic urticaria sera and anti-IgE and subsequent passive sensitization with IgE myeloma serum partially restored it. Stainable peripheral blood basophils/mm3 in chronic urticaria patients were significantly reduced (mean +/- s.e.m, 7.9 +/- 2.0) when compared to healthy controls (39.6 +/- 4.4), P less than 0.001. These results suggest that histamine releasing autoantibodies are important in the pathogenesis of chronic urticaria by stimulating or facilitating degranulation of basophils and cutaneous mast cells through cross-linking cell surface IgE receptors.

Human basophil releasability. VIII. Increased basophil releasability in patients with scleroderma

We evaluated basophil releasability in 16 female patients with scleroderma (systemic sclerosis) and in 16 normal age- and sex-matched donors. Basophils from patients with scleroderma released significantly more histamine "spontaneously" than did those from normal donors (12.9 +/- 2.1% versus 4.5 +/- 0.7%; P less than 0.0005). Basophil reactivity (maximal percentage histamine release) to anti-IgE was higher in patients with scleroderma than in controls (57.0 +/- 7.5% versus 35.4 +/- 7.8%; P less than 0.05). Basophil sensitivity (the concentration of anti-IgE that causes 40% of maximal percentage histamine release) to anti-IgE in scleroderma patients was similar to that found in controls (4.6 +/- 2.8 x 10(-2) micrograms/ml versus 2.3 +/- 1.0 x 10(-1) micrograms/ml; P not significant). Scleroderma patients also showed enhanced releasability compared with that of the controls when challenged in vitro with interleukin-3 (8.3 +/- 1.7% versus 3.2 +/- 0.6%; P less than 0.01). Releasability induced by the formyl-containing tripeptide, f-met peptide, was significantly higher in the scleroderma patients than in the controls at the 2 lower concentrations used. No differences in basophil reactivity and sensitivity to f-met peptide and calcium ionophore A23187 were found between patients and normal donors. These results show that spontaneous basophil releasability and releasability in response to IgE cross-linking and activation of interleukin-3 receptors are increased in patients with scleroderma.

Natural anti-IgE auto-antibodies interfere with diagnostic IgE determination

A simple method is described which enables measurement of anti-IgE antibodies in free form as well as in immune complexes of IgE and anti-IgE. Anti-IgE antibodies were purified from serum of one selected blood donor with highly elevated levels of such autoantibodies. These purified anti-IgE auto-antibodies inhibited the measurement of myeloma IgE. Purification also revealed that 98% of the subject's serum IgE was masked by anti-IgE auto-antibodies. Our data suggest that IgE determinations in sera containing anti-IgE antibodies might be underestimated.