Comparison of the allergic and nonallergic CD4+ T-cell responses to the major dog allergen Can f 1

Single-cell characterization of dog allergen-specific T cells reveals TH2 heterogeneity in allergic individuals

BACKGROUND

Allergen-specific type 2 CD4⁺ T_H2 cells are critically involved in the pathogenesis of IgE-mediated allergic diseases. However, the heterogeneity of the T_H2 response has only recently been appreciated.

OBJECTIVE

We sought to characterize at the single-cell level the ex vivo phenotype, transcriptomic profile, and T-cell receptor (TCR) repertoire of circulating CD4⁺ T cells specific to the major dog allergens Can f 1, Can f 4, and Can f 5 in subjects with and without dog allergy.

METHODS

Dog allergen-specific memory CD4⁺ T cells were detected ex vivo by flow cytometry using a CD154-based enrichment assay and single-cell sorted for targeted gene expression analysis and TCR sequencing.

RESULTS

Dog allergen-specific T-cell responses in allergic subjects were dominantly of T_H2 type. T_H2 cells could be phenotypically further divided into 3 subsets, which consisted of T_H2-like (CCR6^-CXCR3^-CRTH2^-), T_H2 (CCR6^-CXCR3^-CRTH2⁺CD161^-), and T_H2A (CCR6^-CXCR3^-CRTH2⁺CD161⁺CD27^-) cells. All these subsets were nonexistent within the allergen-specific T-cell repertoire of healthy subjects. Single-cell transcriptomic profiling confirmed the T_H2-biased signature in allergen-specific T cells from allergic subjects and revealed a T_H1/T_H17 signature in nonallergic subjects. TCR repertoire analyses showed that dog allergen-specific T cells were diverse and allergic subjects demonstrated less clonality compared to nonallergic donors. Finally, TCR and transcriptomic analyses revealed a close relationship between T_H2-like, T_H2, and T_H2A cells, with the last ones representing the most terminally differentiated and highly polarized subtype.

CONCLUSIONS

Our study demonstrates heterogeneity within allergen-specific T_H2 cells at the single-cell level. The results may be utilized for improving immune monitoring after allergen immunotherapy and for designing targeted immunomodulatory approaches.

The effect of regulatory T cells on tolerance to airborne allergens and allergen immunotherapy

Forkhead box P3-positive regulatory T (Treg) cells are essential mediators of tolerance against self-antigens and harmless exogenous antigens. Treg cell deficiencies result in multiple autoimmune and allergic syndromes in neonates. How Treg cells affect conventional allergies against aeroantigens, which are restricted to a few specific proteins released from inhaled particles, remains controversial. The hallmarks of antigen-specific loss of tolerance are allergen-specific T_H2 cells and IgE. However, difficulties in identifying the rare allergen-specific Treg cells have obscured the cellular basis of tolerance to aeroallergens, which is also a major obstacle for the rational design of novel and more efficient allergen-specific immunotherapies. Recent technological progress allowing characterization of allergen-specific effectors and Treg cells with minimal in vitro manipulation revealed their detailed contribution to tolerance. The data identified inhaled particles as immunodominant Treg cell targets in healthy and allergic subjects. Conversely, the supposed immunodominant major allergens being rapidly released from inhaled particles apparently do not actively induce tolerance but are ignored by the immune system. Here, the partially contradictory data on various allergen-specific T-cell types in healthy subjects, allergic patients, and patients undergoing allergen-specific immunotherapy are discussed and integrated into one model, postulating Treg cell-dependent and Treg cell-independent checkpoints of tolerance and allergy development.

Antigen-specific regulatory T-cell responses against aeroantigens and their role in allergy

The mucosal immune system of the respiratory tract is specialized to continuously monitor the external environment and to protect against invading pathogens, while maintaining tolerance to innocuous inhaled particles. Allergies result from a loss of tolerance against harmless antigens characterized by formation of allergen-specific Th2 cells and IgE. Tolerance is often described as a balance between harmful Th2 cells and various types of protective "regulatory" T cells. However, the identity of the protective T cells in healthy vs. allergic individuals or following successful allergen-specific therapy is controversially discussed. Recent technological progress enabling the identification of antigen-specific effector and regulatory T cells has significantly contributed to our understanding of tolerance. Here we discuss the experimental evidence for the various tolerance mechanisms described. We try to integrate the partially contradictory data into a new model proposing different mechanism of tolerance depending on the quality and quantity of the antigens as well as the way of antigen exposure. Understanding the basis of tolerance is essential for the rational design of novel and more efficient immunotherapies.

Characterization of human memory CD4(+) T-cell responses to the dog allergen Can f 4

BACKGROUND

The recently identified dog lipocalin allergen Can f 4 is an important respiratory allergen.

OBJECTIVE

We sought to comprehensively characterize the memory CD4(+) T-cell responses of allergic and nonallergic subjects to Can f 4.

METHODS

Can f 4-specific CD4(+)CD45RO(+) T-cell lines (TCLs) from allergic and healthy subjects were established and characterized by their functional and phenotypic properties. The epitope specificity of the TCLs was tested with 48 overlapping 16-mer peptides spanning the sequence of Can f 4. HLA restriction of the specific TCLs and the binding capacity of the epitope-containing peptides to common HLA class II molecules were studied.

RESULTS

Can f 4-specific memory CD4(+) TCLs were obtained at an 8-fold higher frequency from allergic than from nonallergic subjects. Functionally, the TCLs of allergic subjects exhibited a higher T-cell receptor avidity and expression of CD25 and predominantly produced IL-4 and IL-5. The TCLs of nonallergic subjects mostly secreted IFN-γ and IL-10, with high CXCR3 expression. Several distinct T-cell epitope regions along the allergen were identified. Importantly, the peptides from the region between amino acids 43 and 67 showed promiscuous HLA-binding capacity and induced memory CD4(+) T-cell responses in 90% of the allergic donors.

CONCLUSION

Productive TH2-deviated memory T-cell responses to Can f 4 are observed in allergic but not nonallergic subjects. A 19-mer peptide sequence covering the core of the immunodominant region of the allergen is a potential target for the development of peptide-based allergen immunotherapy.

HLA class II peptide tetramers vs allergen-induced proliferation for identification of allergen-specific CD4 T cells

BACKGROUND

Fluorescence-labeled MHC class II/peptide tetramer complexes are considered as optimal tools to characterize allergen-specific CD4(+) T cells, but this technique is restricted to frequently expressed HLA class II molecules and knowledge of immunodominant epitopes. In contrast, allergen-stimulated proliferation assessed by CFSE dilution is less sophisticated and widely applicable. The major mugwort allergen, Art v 1, contains only one single, immunodominant, HLA-DR1-restricted epitope (Art v 125-36 ). Thus, essentially all Art v 1-reactive cells should be identified by a HLA-DRB1*01:01/Art v 119-36 tetramer.

METHODS

We compared specificity and sensitivity of tetramer(+) and allergen-induced proliferating (CFSE(lo) ) CD4(+) T cells by flow cytometry.

RESULTS

The frequency of tetramer(+) CD4(+) T cells determined ex vivo in PBMC of mugwort-allergic individuals ranged from 0 to 0.029%. After 2-3 weeks of in vitro expansion, sufficient tetramer(+) T cells for phenotyping were detected in 83% of Art v 125-36 -reactive T-cell lines (TCL) from mugwort-allergic individuals, but not in TCL from healthy individuals. The tetramers defined bona fide Th2 cells. Notably, Art v 125-36 -reactive TCL depleted of tetramer(+) T cells still reacted to the peptide, and only 44% of Art v 125-36 -specific T-cell clones were detected by the tetramer. CFSE(lo) CD4(+) T cells contained only 0.3-10.7% of tetramer(+) T cells and very low proportions of Th2 cells.

CONCLUSION

Allergen-specific T cells can be identified by HLA class II tetramers with high specificity, but unexpected low sensitivity. In contrast, allergen-stimulated CFSE(lo) CD4(+) T cells contain extremely high fractions of bystander cells. Therefore, for T-cell monitoring, either method should be interpreted with caution.

Quantification of circulating house dust mite-specific IL-4- and IL-13-secreting T cells correlates with rhinitis severity in asthmatic children and varies with the seasons

BACKGROUND

Defining suitable markers to diagnose and monitor allergy and its severity is essential to correctly assign patients for specific immunotherapy. Circulating levels of specific IgE are good markers of sensitization, but not of clinically symptomatic allergy.

OBJECTIVE

To quantify circulating interleukin (IL)-4- and IL-13-secreting T cells specific for house dust mite (HDM) in children presenting HDM-allergic asthma associated or not with rhinitis and correlate results with clinical symptoms.

METHODS

We analysed 26 children with HDM respiratory disease (allergic rhinitis and asthma) together with six children with non-allergic asthma. Peripheral blood mononuclear cells were stimulated with HDM extract in a 24-h ELISpot assay to quantify the number of HDM-specific IL-4- and IL-13-secreting T cells. Asthma severity and control, and rhinitis severity were scored according to the Global Initiative for Asthma (GINA) and the Allergic Rhinitis and its Impact on Asthma (ARIA) Guidelines.

RESULTS

The number of HDM-specific IL-4- and IL-13-secreting T cells was higher in patients with allergic asthma as compared to patients with non-allergic asthma. It varied with the season of blood sampling with two peaks in the fall and early spring. Independently of the season, the number of HDM-specific IL-4-secreting T cells correlated with rhinitis severity (OR = 2; 95% IC:1.1-3.8; P = 0.04).

CONCLUSIONS AND CLINICAL RELEVANCE

Allergen-specific IL-4- and IL-13-producing T cells were only detected in HDM-allergic asthmatic children (not in patients with non-allergic asthma). Their numbers correlated with clinical severity of allergic rhinitis.

Human CD4+ T cell responses to the dog major allergen Can f 1 and its human homologue tear lipocalin resemble each other

Lipocalin allergens form a notable group of proteins, as they contain most of the significant respiratory allergens from mammals. The basis for the allergenic capacity of allergens in the lipocalin family, that is, the development of T-helper type 2 immunity against them, is still unresolved. As immunogenicity has been proposed to be a decisive feature of allergens, the purpose of this work was to examine human CD4+ T cell responses to the major dog allergen Can f 1 and to compare them with those to its human homologue, tear lipocalin (TL). For this, specific T cell lines were induced in vitro from the peripheral blood mononuclear cells of Can f 1-allergic and healthy dog dust-exposed subjects with peptides containing the immunodominant T cell epitopes of Can f 1 and the corresponding TL peptides. We found that the frequency of Can f 1 and TL-specific T cells in both subject groups was low and close to each other, the difference being about two-fold. Importantly, we found that the proliferative responses of both Can f 1 and TL-specific T cell lines from allergic subjects were stronger than those from healthy subjects, but that the strength of the responses within the subject groups did not differ between these two antigens. Moreover, the phenotype of the Can f 1 and TL-specific T cell lines, determined by cytokine production and expression of cell surface markers, resembled each other. The HLA system appeared to have a minimal role in explaining the allergenicity of Can f 1, as the allergic and healthy subjects' HLA background did not differ, and HLA binding was very similar between Can f 1 and TL peptides. Along with existing data on lipocalin allergens, we conclude that strong antigenicity is not decisive for the allergenicity of Can f 1.

Immune responses to inhalant Mammalian allergens

In Europe and the USA, at least one person in four is exposed every day to inhalant allergens of mammalian origin, a considerable number is regularly exposed for professional reasons and almost everyone is occasionally exposed to inhalant allergens from pets or domestic animals. The production of IgE to these inhalant allergens, often complicated by asthma and rhinitis, defines the atopic status. However, the immune response to these allergens largely imprints the cellular immune compartment and also drives non-IgE humoral immune responses in the allergic and non-allergic population. During the recent years, it has become clear that IgE antibodies recognize mammalian allergens that belong to three protein or glycoprotein families: the secretoglobins, the lipocalins, and the serum albumins. In this article, we review the humoral and cellular immune responses to the major members of these families and try to define common characteristics and also distinctive features.

Differential CD4+ T-cell responses of allergic and non-allergic subjects to the immunodominant epitope region of the horse major allergen Equ c 1

The responses of allergen-specific CD4(+) T cells of allergic and healthy individuals are still incompletely understood. Our objective was to investigate the functional and phenotypic properties of CD4(+) T cells of horse-allergic and healthy subjects specific to the immunodominant epitope region of the major horse allergen Equ c 1. Specific T-cell lines (TCLs) and clones were generated from peripheral blood mononuclear cells with Equ c 1(143-160), the peptide containing the immunodominant epitope region of Equ c 1. The frequency, proliferative response, cytokine production and HLA restriction of the cells were examined. The frequency of Equ c 1-specific CD4(+) T cells was low (approximately 1 per 10(6) CD4(+) T cells) in both allergic and non-allergic subjects. The cells of allergic subjects had a stronger proliferative capacity than those of non-allergic subjects, and they predominantly emerged from the memory T-cell pool and expressed the T helper type 2 cytokine profile, whereas the cells of non-allergic subjects emerged from the naive T-cell pool and produced low levels of interferon-γ and interleukin-10. T-cell response to Equ c 1(143-160) was restricted by several common HLA class II molecules from both DQ and DR loci. As the phenotypic and functional properties of Equ c 1-specific CD4(+) T cells differ between allergic and non-allergic subjects, allergen-specific T cells appear to be tightly implicated in the development of diseased or healthy outcome. Restriction of the specific CD4(+) T-cell response by multiple HLA alleles suggests that Equ c 1(143-160) is a promising candidate for peptide-based immunotherapy.

Characterization of CD4+ T cell subsets in allergy

Allergen specific T(H)2 cells are a key component of allergic disease, but their characterization has been hindered by technical limitations and lack of epitope data. Knowledge about the factors that drive the differentiation of naïve T cells into allergy-promoting T(H)2 cells and the influence of allergen specific immunotherapy on the phenotype and function of allergen-specific T cells have also been limited. Recent advances indicate that innate and adaptive immune factors drive the development of diverse subsets of allergen-specific T cells. While allergen-specific T cells are present even in non-allergic subjects, highly differentiated T(H)2 cells are present only in allergic subjects and their disappearance correlates with successful immunotherapy. Therefore, elimination of pathogenic T(H)2 cells is an essential step in tolerance induction.

Mammalian lipocalin allergens--insights into their enigmatic allergenicity

Most of the important mammal-derived respiratory allergens, as well as a milk allergen and a few insect allergens, belong to the lipocalin protein family. As mammalian lipocalin allergens are found in dander, saliva and urine, they disperse effectively and are widely present in the indoor environments. Initially, lipocalins were characterized as transport proteins for small, principally hydrophobic molecules, but now they are known to be involved in many other biological functions. Although the amino acid identity between lipocalins is generally at the level of 20-30%, it can be considerably higher. Lipocalin allergens do not exhibit any known physicochemical, functional or structural property that would account for their allergenicity, that is, the capacity to induce T-helper type 2 immunity against them. A distinctive feature of mammalian lipocalin allergens is their poor capacity to stimulate the cellular arm of the human or murine immune system. Nevertheless, they induce IgE production in a large proportion of atopic individuals exposed to the allergen source. The poor capacity of mammalian lipocalin allergens to stimulate the cellular immune system does not appear to result from the function of regulatory T cells. Instead, the T cell epitopes of mammalian lipocalin allergens are few and those examined have proved to be suboptimal. Moreover, the frequency of mammalian lipocalin allergen-specific CD4(+) T cells is very low in the peripheral blood. Importantly, recent research suggests that the lipocalin allergen-specific T cell repertoires differ considerably between allergic and healthy subjects. These observations are compatible with our hypothesis that the way CD4(+) T-helper cells recognize the epitopes of mammalian lipocalin allergens may be implicated in their allergenicity. Indeed, as several lipocalins exhibit homologies of 40-60% over species, mammalian lipocalin allergens may be immunologically at the borderline of self and non-self, which would not allow a strong anti-allergenic immune response against them.

Advances in environmental and occupational respiratory disease in 2010

2010 Found a number of significant advances in environmental and occupational respiratory disease. The role of sensitization and the subsequent production of allergic disease have been explored. New allergens and their T- and B-cell epitopes have been characterized. Novel approaches to the diagnosis and evaluation of food allergy have been described. The role of pollutants as they affect respiratory disease and the effects of age extremes on sensitization and asthma have been addressed. Significant advances in the understanding of inflammatory changes in both the upper and lower respiratory systems occurred. Novel therapeutic approaches have been explored, including the development of hypoallergens from improved molecular biology techniques. New effective approaches to asthma therapy have been identified. Exposure reduction through air filtration and novel immunotherapy approaches, such as sublingual therapy, have made significant advances.

Allergen-specific naïve and memory CD4+ T cells exhibit functional and phenotypic differences between individuals with or without allergy

Although allergen-specific CD4(+) T cells are detectable in the peripheral blood of both individuals with or without allergy, their frequencies and phenotypes within the memory as well as naïve repertoires are incompletely known. Here, we analyzed the DRB1*0401-restricted responses of peripheral blood-derived memory (CD4(+)CD45RO(+)) and naïve (CD4(+)CD45RA(+)) T cells from subjects with or without allergy against the immunodominant epitope of the major cow dander allergen Bos d 2 by HLA class II tetramers in vitro. The frequency of Bos d 2(127-142)-specific memory T cells in the peripheral blood-derived cultures appeared to be higher in subjects with allergy than those without, whereas naïve Bos d 2(127-142)-specific T cells were detectable in the cultures of both groups at nearly the same frequency. Surprisingly, the TCR avidity of Bos d 2(127-142)-specific T cells of naïve origin, as assessed by the intensity of HLA class II tetramer staining, was found to be higher in individuals with allergy. Upon restimulation, long-term Bos d 2(127-142)-specific T-cell lines generated from both memory and naïve T-cell pools from individuals with allergy proliferated more strongly, produced more IL-4 and IL-10, and expressed higher levels of CD25 but lower levels of CXCR3 than the T-cell lines from individuals without allergy, demonstrating differences also at the functional level. Collectively, our current results suggest that not only the memory but also the naïve allergen-specific T-cell repertoires differ between individuals with or without allergy.