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

Regulation of IgE activity in inhalational tolerance via formation of IgG anti-IgE/IgE immune complexes

Background

Allergic asthma is an inflammatory disorder of the airways that results from inappropriate production of IgE against harmless, environmental antigens. Sequestration of free IgE using humanized IgG anti-IgE is an effective therapy for asthma and other atopic disorders. However, the status of free IgE in subjects who have naturally developed immune tolerance to inhaled antigens has not been well studied.

Methods

C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) for 7 days to induce allergic airway disease (AAD) or 6 weeks to induce a state of local inhalational tolerance (LIT). Serum from AAD or LIT mice, diluted to achieve equivalent levels of total OVA-specific IgE, was used to sensitize rat basophil leukemia cells for allergen-mediated degranulation. Levels of degranulation were measured in relation to serum concentrations of free IgE and IgG anti-IgE/IgE immune complexes.

Results

Serum from AAD animals induced a greater degree of basophil degranulation than serum from LIT animals. These results correlated with higher levels of free IgE in AAD animals, whereas LIT mice demonstrated a significant increase in IgG anti-IgE/IgE immune complexes relative to their diseased counterparts.

Conclusions

Sequestration of free IgE by naturally occurring IgG anti-IgE may aid in the development of immune tolerance against inhaled allergens. The decrease in bioavailability of free IgE may, in turn, contribute to the overall reduction of asthma symptoms via a mechanism that mimics the therapeutic effects of humanized IgG anti-IgE.

"Auto-anti-IgE": naturally occurring IgG anti-IgE antibodies may inhibit allergen-induced basophil activation

Background

Naturally occurring IgE-specific IgG autoantibodies have been identified in patients with asthma and other diseases, but their spectrum of functions is poorly understood.

Objective

Address the hypothesis that: (i) IgG anti-IgE autoantibodies are detectable in the serum of all subjects but elevated in asthmatic patients regardless of atopic status as compared with controls; (ii) some activate IgE-sensitized basophils; and (iii) some inhibit allergen-induced basophil activation.

Methods

IgE-specific IgG autoantibodies were detected and quantified in sera using ELISA. Sera were examined for their ability to activate IgE-sensitized human blood basophils in the presence and absence of allergen using a basophil activation test, and to inhibit allergen binding to specific IgE on a rat basophilic cell line stably expressing human FcεRI.

Results

IgG autoantibodies binding to both free and FcεRI-bound IgE were detected in patients with atopic and non-atopic asthma, as well as controls. While some were able to activate IgE-sensitised basophils, others inhibited allergen-induced basophil activation, at least partly by inhibiting binding of IgE to specific allergen.

Conclusion

Naturally occurring IgG anti-IgE autoantibodies may inhibit, as well as induce, basophil activation. They act in a manner distinct from therapeutic IgG anti-IgE antibodies such as omalizumab. They may at least partly explain why atopic subjects who make allergen-specific IgE never develop clinical symptoms, and why omalizumab therapy is of variable clinical benefit in severe atopic asthma.

Receptor Interacting Protein 2 (RIP2) Is Dispensable for OVA-Induced Airway Inflammation in Mice

Purpose

Asthma is a pulmonary chronic inflammatory disease characterized by airway obstruction and hyperresponsiveness. Pattern recognition receptors are known to play a key role in the development of allergic diseases as well as host defenses against microbial infection. Receptor interacting protein 2 (RIP2), a serine/threonine kinase, is an adaptor molecule of NOD1 and NOD2, and genetic variation in this receptor is known to be associated with the severity of allergic asthma in children. In this study, we examined the role of RIP2 in the development of allergic airway inflammation in a mouse model.

Methods

Airway inflammation was induced in mice through intranasal administration of ovalbumin (OVA) after 2 intraperitoneal immunizations with OVA. Lung inflammation and mucus hypersecretion were examined histologically and total cell infiltration in bronchoalveolar (BAL) fluids was determined. Levels of the Th2-related cytokines, IL-5 and IL-13, in lung extracts were measured by ELISA. Serum antigen-specific IgE and IgG1 levels were also assessed.

Results

OVA-induced lung inflammation and mucus hypersecretion were not different between WT and RIP2-deficient mice. The IL-5 and IL-13 levels in the bronchoalveolar (BAL) fluids were also not impaired in RIP2-deficient mice compared to WT mice. Moreover, RIP2 deficiency did not affect serum OVA-specific IgG1 and IgE levels.

Conclusions

Our results suggest that RIP2 is not associated with the development of allergic airway inflammation.

FcRn-mediated intestinal absorption of IgG anti-IgE/IgE immune complexes in mice

BACKGROUND

The mechanism(s) responsible for the acquisition of maternal antibody isotypes other than IgG are not fully understood.

OBJECTIVE

To define the ability of the neonatal Fc receptor for IgG uptake (FcRn) to mediate intestinal absorption of IgG(1) anti-IgE/IgE immune complexes.

METHODS

C57BL/6 allergic ovalbumin (OVA)-immune foster mothers were generated to nurse naïve FcRn(+/-) or FcRn(-/-) progeny. At the time of weaning, serum levels of OVA-specific antibodies and IgG(1) anti-IgE/IgE immune complexes were determined in allergic foster mothers and FcRn(+/+), FcRn(+/-), or FcRn(-/-) breastfed offspring. In separate experiments, FcRn(+/-) or FcRn(-/-) neonatal mice were gavage fed TNP-specific IgE as IgG(1) anti-IgE/IgE immune complexes, IgG(1) isotype control and IgE, or IgE alone. Mice were killed 2 h after feeding to determine serum levels and biological activity of absorbed TNP-specific IgE.

RESULTS

As expected, the absorption of maternal OVA-specific IgG(1) in FcRn(-/-) offspring was at levels 10(3) -10(4) less than observed in FcRn(+/+) or FcRn(+/-) offspring. Surprisingly, FcRn expression also influenced the absorption of maternal IgE. OVA-specific IgE was detected in FcRn(+/+) and FcRn(+/-) offspring, but not in FcRn(-/-) offspring. IgG(1) anti-IgE/IgE immune complexes were detected in allergic foster mothers and correlated strongly with levels in FcRn(+/+) and FcRn(+/-) offspring (ρ = 0.88, P < 0.0001). Furthermore, FcRn expression was required for neonatal mice to absorb TNP-specific IgE when fed as IgG(1) anti-IgE/IgE immune complexes. When immune complexes were generated with IgG(1) anti-IgE directed against the Cε4 domain, the absorbed IgE was able to function in antigen-dependent basophil degranulation.

CONCLUSIONS AND CLINICAL RELEVANCE

These data demonstrate a novel mechanism by which FcRn may facilitate absorption of maternal antibodies other than IgG. These findings are clinically relevant because FcRn mediates the transplacental passage of maternal IgG to the fetus. This raises the possibility that FcRn could mediate the transplacental passage of maternal IgE as IgG anti-IgE/IgE immune complexes.

Circulating IgG autoanti-IgE antibodies in atopic patients block the binding of IgE to its low affinity receptor (CD23)

Aims-To investigate the ability of circulating IgG autoanti-IgE antibodies from atopic rhinitis patients to block the binding of IgE to its low affinity receptor (FcepsilonRII), also termed CD23.Methods-This involved the use of a well validated flow cytometric method to detect inhibition of FITC labelled IgE binding to human B cells expressing CD23 (RPMI 8866 cell line).Results-Taking inhibition values greater than 20% as being significant, 15 out of 20 IgG anti-IgE containing sera inhibited the binding of IgE-FITC to the RPMI 8866 cells. The inhibitory effect was recoverable in the IgG fraction of serum, but was not related to the titre of either IgG1 anti-IgE or IgG4 anti-IgE, thus suggesting that it might be related to epitope specificity. No such inhibition was demonstrable with rheumatoid sera containing autoanti-IgG (that is, rheumatoid factor), but lacking autoanti-IgE.Conclusions-The capacity of anti-IgE to block the binding of IgE to CD23 has important implications, particularly in terms of upregulation of IgE synthesis and the consequent perpetuation of the inflammatory response.

Circulating human IgG autoanti-IgE antibodies in asthma patients block the binding of IgE to its high affinity receptor

Aims-To investigate the ability of circulating human IgG autoanti-IgE antibodies from asthma patients to block the binding of IgE to the alpha chain of the high affinity receptor (FcepsilonRI).Methods-This involved the use of a well validated flow cytometric method to detect inhibition of FITC labelled IgE binding to a fibroblast cell line (CHK1E1) transfected with the alpha chain of FcepsilonRI.Results-IgG autoanti-IgE-containing sera blocked the binding of IgE-FITC to the CHK1E1 cells. No such inhibition was demonstrable with rheumatoid sera containing autoanti-IgG (that is, rheumatoid factor) but lacking autoanti-IgE. Percentage inhibition (up to 50%) of IgE binding to the CHK1E1 cells was directly related to the titre of IgG1, but not IgG4, autoanti-IgE in the sera tested (correlation coefficient 0.66, probability 0.003).Conclusions-The capacity of anti-IgE to block the binding of IgE to FcepsilonRI has important clinical implications, particularly in terms of downregulation of allergic reactions.

The prevalence of IgE antibody reactivity against the alkaline serine protease major allergen of Penicillium chrysogenum increases with the age of asthmatic patients

BACKGROUND

Penicillium species are prevalent airborne fungi. However, the prevalence of allergic sensitization to Penicillium antigens and the true impact of these ubiquitous fungi on atopic respiratory disorders remain to be determined.

OBJECTIVE

The purpose of this study was to analyze the prevalence of immunoglobulin (Ig)E and IgG antibodies against Penicillium chrysogenum (Pen ch 13), the alkaline serine protease major allergen of P. chrysogenum, in asthmatic patients of different age groups.

METHODS

Pen ch 13 was purified from a culture medium of P. chrysogenum. The reactivity of IgE and IgG antibodies to Pen ch 13 in the serum samples of 212 asthmatic patients was analyzed by immunoblotting methods.

RESULTS

Sixty-nine (33%) of the 212 sera analyzed showed IgE and/or IgG immunoblot reactivity to Pen ch 13. Significant differences in the prevalence of IgE and/or IgG antibody reactivity to Pen ch 13 were found among eight different age groups of 212 asthmatic patients. The frequency of IgE-binding reactivity to Pen ch 13 increased significantly with the age of the patients. It was 7% for the group less than 10 years old and 42% for the group older than 70 years old. In addition, a significant difference between the prevalence of IgE (7%) and IgG (33%) antibodies against Pen ch 13 in the group aged 10 or less was also found.

CONCLUSIONS

Our study demonstrates that IgE and IgG antibodies specific for Pen ch 13 were detected in approximately one-third of the 212 asthmatic patients analyzed. Our results suggest that allergic sensitization to Pen ch 13, and possibly to other airborne Penicillium species, is more common in older asthmatic patients.

Autoanti-IgE antibodies in patients with allergic and idiopathic rhinitis

The pathophysiology of idiopathic rhinitis is unknown although evidence is accumulating to suggest that, in a proportion of patients, it may be a more localized form of allergic rhinitis in the absence of other atopic symptoms and markers. Anti-IgE is thought to be a systemic marker of atopy. This study compared serum IgG autoanti-IgE levels in patients with idiopathic rhinitis, perennial allergic rhinitis and normal controls. Serum samples were obtained from 19 patients with idiopathic rhinitis, 17 patients with perennial allergic rhinitis and 10 normal non-rhinitic controls. The presence or absence of IgG1 and IgG4 anti-IgE antibodies was detected using enzyme-linked immunosorbent assays. Eighty-eight percent of the patients with perennial allergic rhinitis had raised levels of autoanti-IgE antibodies in their serum. None of the controls or patients with idiopathic rhinitis showed raised levels (P < 0.001). Although patients with idiopathic rhinitis may exhibit clinical and pathological features of allergy, they do not show raised levels of anti-IgE in their serum.

Asthma: a dynamic disease of inflammation and repair

It is now widely accepted that asthma in its varied forms is an inflammatory disorder of the airways in which mediator release from activated mast cells and eosinophils plays a major role. T lymphocytes take a primary role in orchestrating these processes through their capacity to generate a range of cytokines of the interleukin 4 gene cluster encoded on the long arm of chromosome 5. Additional cytokines derived from mast cells and eosinophils also play a key role, especially tumour necrosis factor alpha, which is responsible for initiating the up-regulation of vascular adhesion molecules involved in the recruitment of eosinophils and other inflammatory cells from the circulation. The importance of C-X-C and C-C chemokines as local chemoattractants and activating stimuli is also recognized. In addition to releasing an array of pharmacologically active autacoids, the inflammatory response in asthma results in the generation of proteolytic activities from mast cells (tryptase, chymase), eosinophils (MMP-9) and the epithelium itself (MMP-2, MMP-9), which exert tissue-destructive and cell-signalling effects. The epithelium is also highly activated, as evidenced by the up-regulation of cytokine production, inducible enzymes and soluble mediators. Increased surface expression of the epithelial isoform of CD44 (9v) and subepithelial proliferation of myofibroblasts are indicative of a simultaneous active repair process and the laying down of new interstitial collagens. Together, inflammatory and repair processes create the complex phenotype that characterizes asthma and its progression.

The prevalence of IgG1 and IgG4 autoantibodies to IgE in patients with allergic and non-allergic rhinitis

In this study we have compared the levels of IgG1 and IgG4 autoantibodies to IgE in the sera of patients with allergic rhinitis and non-allergic rhinitis. A group of patients undergoing cosmetic nasal surgery, but who did not have rhinitis or any history of atopy, acted as control. The frequency of positive titres of IgG1 and/or IgG4 anti-IgE was 70% (14/20) in patients with allergic rhinitis, 50% (10/20) in patients with non-allergic rhinitis and 20% (4/20) in the control group. The mean titres of IgG1 anti-IgE and IgG4 anti-IgE were in the order allergic rhinitis > non-allergic rhinitis > controls. In the allergic rhinitis group levels of IgG1 anti-IgE (P = 0.0055) and IgG4 anti-IgE (P = 0.0028) were significantly higher than those found in the control group. The non-allergic rhinitis group also showed significantly higher levels of IgG1 anti-IgE (P = 0.0182) and IgG4 and anti-IgE (P = 0.0359) than the control group. The existence of IgG autoantibodies to IgE in both allergic and non-allergic rhinitis suggests a possible role for these antibodies in the disease process, particularly in patients whose symptoms are not due to an allergic trigger.