Mite allergy is associated with a specific profile of IgG epitopes recognized on antigen p1 of Dermatophagoides pteronyssinus

An Allergen Portrait Gallery: Representative Structures and an Overview of IgE Binding Surfaces

Recent progress in the biochemical classification and structural determination of allergens and allergen-antibody complexes has enhanced our understanding of the molecular determinants of allergenicity. Databases of allergens and their epitopes have facilitated the clustering of allergens according to their sequences and, more recently, their structures. Groups of similar sequences are identified for allergenic proteins from diverse sources, and all allergens are classified into a limited number of protein structural families. A gallery of experimental structures selected from the protein classes with the largest number of allergens demonstrate the structural diversity of the allergen universe. Further comparison of these structures and identification of areas that are different from innocuous proteins within the same protein family can be used to identify features specific to known allergens. Experimental and computational results related to the determination of IgE binding surfaces and methods to define allergen-specific motifs are highlighted.

Sublingual immunotherapy of allergic diseases

The only disease-modifying treatment that is available for allergic patients is allergen-specific immunotherapy. Two competing application forms are used: subcutaneous immunotherapy, which has been used for > 90 years, and a relatively new immunotherapy where the allergen is applied sublingually. Numerous studies have shown efficacy for subcutaneous immunotherapy and have identified possible mechanisms that are responsible for the observed reduction in allergic responses. In contrast, the efficacy of sublingual immunotherapy has not been documented to the same degree and the responsible immunological mechanisms have not yet been clearly defined. This review focuses on the published clinical and experimental data on sublingual immunotherapy and points at possible mechanisms of how sublingual immunotherapy may differ from subcutaneous immunotherapy in its mode of action, and also discusses the potential advantages and pit falls of both therapies.

Mechanisms of immunotherapy: IgG revisited

PURPOSE OF REVIEW

This paper will review historical and recent evidence for the induction of 'blocking' IgG antibodies during successful specific immunotherapy.

RECENT FINDINGS

Specific immunotherapy is frequently associated with a rise in allergen-specific IgG4 antibodies and a modest reduction in specific IgE titres, although this does not always correlate with clinical efficacy. There is accumulating evidence that specific immunotherapy also influences the blocking activity on IgE-mediated responses by IgG4, and cellular assays are commonly used to investigate these changes. Recently, a novel assay, which detects allergen-IgE binding using flow cytometry, has been used to detect 'functional' specific immunotherapy-induced changes in IgG antibody activity. Results suggest that successful specific immunotherapy is associated with an increase in IgG blocking activity that is not solely dependent on the quantity of IgG antibodies.

SUMMARY

Successful immunotherapy is associated with quantitative and qualitative changes in the allergen-specific IgG antibody response. The induction of IgG antibodies with blocking activity may have a protective role not only through the inhibition of allergen-induced, IgE-mediated release of inflammatory mediators from mast cells and basophils, but also through the inhibition of IgE-facilitated antigen presentation to T cells. Qualitative changes in the allergen-specific IgG antibody response may possibly be an important mechanism underlying the clinical efficacy of specific immunotherapy. Monitoring changes in blocking activity using cellular assays may give an early indication of the potential success of treatment.

Chitosan nanoparticles containing plasmid DNA encoding house dust mite allergen, Der p 1 for oral vaccination in mice

Our previous studies indicated that intramuscular (i.m.) immunisation with full length Der p 1 cDNA induced significant humoral response to the left domain (approximately corresponding to amino acids 1-116) but not to the right domain (approximately corresponding to amino acids 117-222) of Der p 1 allergen. This study explored the use of chitosan-DNA nanoparticles for oral immunisation to induce immune responses specific to both the left and right domains of Der p 1. DNA constructs pDer p 1 (1-222) and pDer p 1 (114-222) were complexed with chitosan and delivered orally followed by an i.m. injection of pDer p 1 (1-222) 13 weeks later. Such approach has successfully primed Th1-skewed immune responses against both domains of Der p 1. This strategy could be further optimised for more efficacious gene vaccination for full length Der p 1.

Expression of FcgammaRIII (CD16) on human peripheral blood eosinophils increases in allergic conditions

BACKGROUND

Blood eosinophils have mRNA for FcgammaRIIIB (CD16) but no or minimal spontaneous CD16 expression. Because IFN-gamma and chemotactic factors induce eosinophil CD16 expression in vitro, we postulated that blood eosinophils could express CD16.

OBJECTIVE

Blood of nonallergic controls and subjects with allergic rhinitis, allergic and nonallergic asthma, or hypereosinophilia of various etiologies were analyzed for leukocyte CD16 surface expression.

METHODS

CD16(+) eosinophils were identified on the basis of physico-optic characteristics, major basic protein, CD49b expression, and sorting by flow cytometry and microscope examination.

RESULTS

Subjects with allergic rhinitis and subjects with asthma had higher median percentages of CD16(+) eosinophils (8.1% [1% to 48.6%] and 7.3% [1.4% to 31.1%], respectively) than nonallergic controls and nonallergic asthmatics (3% [0% to 11%] and 4.6% [2.9% to 5.1%], respectively). In subjects with hypereosinophilia, CD16(+) eosinophils were increased only in a case of drug allergy. When subjects with mild allergic asthma were challenged with a relevant aeroallergen, blood CD16(+) eosinophils further increased during or after the late-phase response (6 to 48 hours after challenge; mean +/- SEM, 9.4% +/- 2.5% to 20.0% +/- 3.0%). CD16(+) eosinophils expressed more IL-5 receptor but less CD11b and IL-12p35 than did CD16(-) eosinophils.

CONCLUSION

Upregulation of blood CD16(+) eosinophils in allergic conditions and its association with a modified phenotype suggest that CD16 receptor could play a role in eosinophil activation in allergy.

Characterization of polyclonal allergen-specific IgE responses by affinity distributions

Polyclonal IgE responses have been previously characterized by allergen-specific antibody levels and by identification of amino acid sequences related to immunodominant epitopes. However, the binding affinities related to these antibody families are not well known. Using sera from donors with known sensitivities to ragweed or house dust mite allergens, we studied the binding reactions between the purified allergens Amb a 1 and Der p 1 and allergen-specific IgE's by determining affinity distribution functions. The distributions of binding affinities only exhibited a few dominant reactions indicated by peaks in an affinity distribution display. In all the donors tested, there were two dominant peaks and in 2/3 of the cases there was a third peak for both Amb a 1 and Der p 1. We further characterized the polyclonal interactions between IgE and Der p 1 by inhibiting the specific binding of IgE using peptide fragments known to be constituents of Der p 1 epitopes. Each peptide inhibited only a single peak in the affinity distributions. It would appear that the peaks in the affinity distribution represent antibodies directed to single epitopes. These results suggest that in our atopic population the response is surprisingly uniform. The bulk of the IgE response (70-80%) is of high affinity (10(8)-10(11) M(-1)) and directed towards a few epitopes. The relative affinities towards epitopes seem to be determined by the structure of the epitope and not variations of individuals' immune responses.

Early effect of ultrarush venom immunotherapy on the IgG antibody response

BACKGROUND

We have previously shown in several allergy models that allergic and tolerance status with respect to allergens is associated with a somewhat different dominant specificity of IgG antibodies. The objective was to test this hypothesis in the compelling model of ultrarush venom immunotherapy (VIT), which induces clinical tolerance after only a few hours of treatment.

METHODS

Antibody titers and specificity were evaluated through solid-phase ELISA using streptavidin-biotin technology in 12 patients allergic to wasp venom before and during the ultrarush procedure (at 12 h, 24 h, and 15 days). The results were compared with those from another group of 20 patients treated with venom injections for at least 2 years.

RESULTS

No significant change was observed in IgG titers during the early phase of VIT. The capacity of individual sera to prevent the antigen binding of pooled IgG from allergic patients changed rapidly, with mean percentage inhibitions falling from 80+/-15%, before starting VIT, to 26+/-14%, 35+/-15%, and 34+/-5% after 12 h, 24 h, and 15 days of treatment, respectively (P<0.001 by one-way ANOVA). The capacity of individual sera to prevent the antigen binding of pooled IgG from patients receiving prolonged VIT changed, with mean percent inhibitions increasing from 47+/-8%, before starting VIT, to 76+/-7%, 83+/-6%, and 87+/-6% after 12 h, 24 h, and 15 days of treatment, respectively (P<0.001 by one-way ANOVA).

CONCLUSIONS

During the initial phase of ultrarush VIT, a change in IgG specificity, i.e., a change in the set of epitopes dominantly recognized by IgG on wasp-venom antigens, occurred concomitantly with early clinical tolerance and was already detectable a few hours after the onset of treatment. Although it may be an epiphenomenon, this change represents the earliest humoral modification described so far during this procedure. The mechanism is unknown, but it appears to be a selective depletion of the highest avidity antibody fraction by the venom injected in large doses at this stage of therapy. Finally, our data now show the previously documented association between a particular IgG specificity and the clinical status (allergy vs tolerance) to be true also with ultrarush VIT, a model in which the clinical ability to display allergic symptoms is rapidly reversed.

Relationship between allergic status and specificity of IgG antibody to inhaled allergens: the grass pollen model

BACKGROUND

We have previously reported that IgG antibodies from healthy individuals and patients suffering from non-seasonal mite allergy bind to different sets of epitopes on Der p 1, allowing almost complete discrimination of the populations.

OBJECTIVES

To confirm this observation in a seasonal allergy model where a clear relationship between allergic symptoms and exposure to the offending agent is established. To investigate whether the pattern of modified specificity is related to the differences in IgG subclass hierarchy usually exhibited by nonallergic and allergic populations.

METHODS

The capacity of individual sera from patients allergic to grass pollen and healthy individuals, including grass pollen-sensitized subjects, to prevent the binding of pooled IgG, IgG1, and IgG4 fractions from grass pollen-allergic patients and healthy individuals to solid-phase bound grass pollen antigen was evaluated in enzyme-linked immunosorbent assay (ELISA) using streptavidin-biotin technology. Specificity controls were performed using sera from patients allergic to cat dander and house dust mite.

RESULTS

The capacity of sera to prevent the antigen binding of allergic IgG averaged 84 +/- 5% for allergic sera and 53 +/- 6% for healthy sera (P < 0.001 by one-way anova). Conversely, using the antigen-binding capacity of healthy control IgG as reference, percentage inhibitions averaged 46 +/- 9% in grass pollen-allergic subjects compared with 80 +/- 4%, 82 +/- 2% in healthy individuals, and mite- and cat-allergic patients, respectively, resulting in two well-separated populations (P < 0.0001 by one-way anova). Similar results were found regardless of whether pooled IgG1 or IgG4 were used.

CONCLUSION

Together with previous data, our results define a new type of humoral signature in the immune response to inhaled allergens. Allergic and healthy status differ not only in the presence or absence of specific IgE antibody but also in the preferential expression of distinct IgG specificities that are better correlated with clinical manifestations and are unrelated to subclass distribution.

Anti-betalactoglobulin IgG antibodies bind to a specific profile of epitopes when patients are allergic to cow's milk proteins

BACKGROUND

We demonstrated recently that mite-allergic patients differed from healthy controls in the specificity of their IgG antibodies towards mite antigens.

OBJECTIVE

The present study investigates whether these discriminatory IgG responses could be associated with the expression and the evolution of clinical manifestations in allergy to cow's milk proteins.

METHODS

Antibody specificity was evaluated by comparing IgG-binding to native bovine beta-lactoglobulin (nBLG) and its products of pepsin hydrolysis (dBLG) using a solid-phase enzyme-linked immunosorbent assay (ELISA). Antibody specificity was further investigated in competitive ELISA using streptavidin-biotin technology with purified IgG fractions from selected subjects and specific mouse monoclonals raised against BLG.

RESULTS

IgG antibodies from CM-intolerant or allergic sera (n=222) showed a higher degree of binding to nBLG than to dBLG, while control sera showed similar levels to both nBLG and dBLG (n=99 children/65 adults). Sera from symptomatic patients, wether or not they contained IgE antibodies, demonstrated group-segregating capacities to compete with pooled purified IgG from each clinical class, and with selected murine anti-nBLG monoclonal antibodies for binding to n- and dBLG. Furthermore, this inhibitory capacity shifted dramatically in a small subset (n=14) of children as they developed CM-tolerance.

CONCLUSIONS

The IgG responses to BLG of CM-intolerant or allergic patients are very different from those of healthy controls, being characterized not only by increased titres but also similar patterns of modified specificity, including a marked preference for conformational epitopes. Cross-competition experiments confirmed that the restricted specificity was clinically associated, appearing as an immunological signature, which allowed almost complete discrimination between patient groups. This phenomenon is a particularly promising diagnostic feature in this category of young patients where conventional tests usually only document the status of sensitization.

Modified antigenic reactivity of anti-phospholipase A2 IgG antibodies in patients allergic to bee venom: conversion with immunotherapy and relation to subclass expression

BACKGROUND

We have previously reported that, in addition to modifying IgG levels and subclass distributions, wasp venom immunotherapy (VIT) rapidly changes IgG antibody specificity.

OBJECTIVES

We investigated whether such a change can be documented in the IgG response to the major bee venom allergen, phospholipase A2 (PLA2), from patients allergic to bees treated with VIT; whether it is coupled to the shift in IgG subclass distribution (IgG4 predominance) usually observed during VIT; and whether it restores the specificity displayed by IgG antibodies from nonallergic individuals.

METHODS

Antibody specificity was evaluated in 17 patients allergic to bee venom in competitive ELISAs by using streptavidin biotin technology. Patients were tested before and during specific immunotherapy (at 15 days and 6 months) and compared with another group of 17 patients treated with venom injections for at least 2 years (VIT patients) and 30 healthy individuals.

RESULTS

The capacity of individual sera to prevent PLA2 binding of pooled IgG from allergic patients changed rapidly with mean percentage inhibitions falling from 84% +/- 14% before starting VIT to 27% +/- 13% and 28% +/- 7% after 15 days and 6 months of treatment, respectively (p < 0.001 by one-way analysis of variance [ANOVA]). IgG titers were only slightly increased. The capacity of individual sera to prevent the binding of pooled IgG from patients receiving VIT changed rapidly with mean percentage inhibition increasing from 60% +/- 12% before starting VIT to 85% +/- 6% and 82% +/- 6% after 15 days and 6 months of treatment, respectively (p < 0.001 by one-way ANOVA). Similar results were found regardless of whether pooled IgG1 or pooled IgG4 were used.

CONCLUSION

VIT results in a rapid change in the antigenic reactivity of anti-PLA2 IgG antibody of human allergic sera, restoring, although not completely, the specificity peculiar to lgG from healthy individuals. This suggests that allergic status and immunoprotection correlate with the preferential expression of distinct IgG specificities, which appear equally distributed over the IgG1 and IgG4 antibody subclasses. It is, however, not known whether the shift in IgG specificity is one of the operative mechanisms of VIT.

Wasp venom immunotherapy changes IgG antibody specificity

BACKGROUND

The evolution of the IgG response during venom immunotherapy (VIT) has been previously investigated in terms of antibody titres and subclasses.

OBJECTIVES

The present work studied the evolution of IgG antibody fine specificity in wasp allergic patients treated with rush VIT.

METHODS

Antibody specificity was evaluated in 51 wasp allergic patients in competitive ELISA using streptavidin biotin technology. Patients were tested before and during specific rush immunotherapy (at 15 days, 6 months, 12 months) and compared with 44 patients treated by venom injections for at least 2 years.

RESULTS

The capacity of sera to prevent the antigen binding of pooled IgG from allergic patients changed rapidly with mean percentage inhibitions (+/-SD) falling from 70+/-11-51+/-18% after 15 days of treatment (P<0.001 by one way ANOVA). Similarly, the antigen binding capacity of pooled IgG from VIT patients was differently prevented by sera with mean percentage inhibitions increasing from 37+/-12-65+/-8 after 15 days of treatment (P< 0.0001 by one-way ANOVA).

CONCLUSIONS

The immunodominance pattern of IgG epitopes recognized on wasp venom antigens by sera from wasp allergic patients changes soon after initiating rush VIT. Further studies will indicate whether, instead of measuring IgG titres, this marked change could be used as the basis of a new test for monitoring the outcome of VIT.