Peanut allergic subjects' peripheral blood mononuclear cell proliferative responses to crude peanut protein

Lymphoproliferative responses to dendritic cell presentation of sensitizing allergens in atopic children with multiple allergies

BACKGROUND

Peripheral blood mononuclear cells (PBMCs) proliferate inconsistently, rendering current lymphoproliferation assays unreliable in diagnosis.

OBJECTIVE

To investigate the utility and nature of proliferation responses in allergy by comparison of the standard lymphoproliferation with a new dendritic cell (DC) stimulated assay.

METHODS

Monocyte-derived DCs were pulsed with allergens and incubated with autologous T cells for 7 days. DC-stimulated and standard PBMC proliferation responses to 3 common dietary allergens in children with allergy and without atopy were measured by incorporation of tritiated thymidine and reduction of carboxyl fluorescein succinimidyl ester staining.

RESULTS

The DC presentation of sensitizing allergens induced significantly higher proliferative responses than PBMC stimulation (P = .04) and greater distinction between normal and allergic responses. DC-induced stimulation indices of children without sensitivity and those with allergy were significantly different with all 3 foods (P < .001). All children with allergy presented with peanut allergy and 12 of 14 (86%) β-lactoglobulin-pulsed DC preparations proliferated more than 3.3-fold above un-pulsed cells, but 8 of 18 children (44%) with ovalbumin egg allergy showed proliferation below this level. The stimulation index of DC tritiated thymidine incorporation correlated closely with carboxyl fluorescein succinimidyl ester reduction (P < .001). Sensitivity of detection of peanut, milk, or egg allergy was 100%, 85.7%, or 55.6% and specificity was 60%, 88.9%, or 86.7%, respectively. DC-stimulated T cells expressed increased levels of CD45 RO and CD25 and most produced interferon-γ. DC-stimulated proliferation correlated with total immunoglobulin E and peanut antigen-stimulated proliferation correlated with peanut specific immunoglobulin E (P = .03).

CONCLUSION

The DC-induced lymphoproliferation had higher sensitivity, specificity, and reproducibility than the standard assay and caused increased memory and activated T-cell proliferation in children with food allergy.

Markers of tolerance development to food allergens

IgE-mediated reactions to food allergens are the most common cause of anaphylaxis in childhood. Although allergies to cow's milk, egg, or soy proteins, in contrast to peanut and tree nut allergens, resolve within the first 6 years of life in up to 60% due to natural tolerance development, this process is not well understood. At present, there is no cure or treatment for food allergy that would result in an induction of tolerance to the symptom-eliciting food. Avoidance, providing an emergency plan and education, is the standard of treatment. Oral immunotherapeutic approaches have been proven reasonable efficacy; however, they are associated with high rates of side-effects and low numbers of patients achieving tolerance. Nevertheless, mechanisms that take place during oral immunotherapy may help to understand tolerance development. On the basis of these therapeutic interventions, events like loss of basophil activation and induction of regulatory lymphocyte subsets and of blocking antibodies have been described. Their functional importance at a clinical level, however, remains to be investigated in detail. Consequently, there is eminent need to understand the process of tolerance development to food allergens and define biomarkers to develop and monitor new treatment strategies for food allergy.

Beyond skin testing: state of the art and new horizons in food allergy diagnostic testing

Food allergy affects approximately 1% to 10.8% of the general population, and its prevalence seems to be increasing. An accurate diagnosis is particularly important because a misdiagnosis could lead to life-threatening reactions or to unnecessary restrictive diets. However, allergy tests currently used in clinical practice have limited accuracy, and an oral food challenge, considered as the gold standard, is often required to confirm or exclude a food allergy. This article reviews several promising novel approaches for the diagnosis of food allergy, such as new molecular diagnostic technologies and functional assays, along with their potential clinical applications.

Cutaneous lymphocyte antigen and α4β7 T-lymphocyte responses are associated with peanut allergy and tolerance in children

BACKGROUND

It is unclear whether the initial route of allergen exposure in early life could influence the subsequent development of allergy, with cutaneous sensitization leading to peanut allergy (PA), and tolerance induced by oral exposure. The skin- and gastrointestinal (GI)-homing markers, cutaneous lymphocyte antigen (CLA) and α4β7 integrin, are used to determine whether the state of PA correlates with peanut-specific CLA responses, with tolerance associated with predominant α4β7 responses.

METHODS

CLA+ and α4β7+ memory T cells were isolated and cultured with peanut extract to assess their proliferation. Stimulation indices were compared in peanut allergic and non-allergic (NA) groups, and peanut-specific cytokine production was measured.

RESULTS

In peanut allergic patients, peanut-specific proliferation predominates in the skin-homing CLA+ subset, whilst peanut-tolerant groups have a mixed CLA/α4β7 response (P = 0.008). Comparison with a control food antigen (ovalbumin) showed that these differences are allergen specific. Cytokine responses showed trends towards Th1 skewing in the GI-homing α4β7+ cells of peanut-tolerant groups and Th2 skewing in the skin-homing CLA+ cells of peanut allergic patients.

CONCLUSION

The predominance of the CLA+ response to peanut in peanut allergic patients is consistent with the hypothesis that allergic sensitization occurs through the skin. The predominant α4β7+ response in peanut-tolerant groups suggests that allergen exposure through the GI tract induces tolerance.

IgE-mediated facilitated antigen presentation underlies higher immune responses in peanut allergy

BACKGROUND

Peanut allergy poses significant healthcare problems, because its prevalence is increasing in many countries, and it is rarely outgrown. To explore the immunological mechanisms that underlie peanut allergy and tolerance, we compared the peanut-specific responses of peanut-allergic (PA) and nonallergic (NA) individuals.

METHODS

We measured peanut-specific peripheral blood mononuclear cells (PBMC) proliferation using tritiated thymidine. The frequency of peanut-specific T cells amongst PBMC was determined by carboxyfluorescein succinimidyl ester labelling. The role of IgE-dependent facilitated antigen presentation (FAP) in modulating proliferation was investigated by depleting IgE from plasma with anti-IgE-coated beads and then assessing PBMC proliferation in the presence of IgE-depleted or nondepleted plasma.

RESULTS

We found that peanut-specific PBMC proliferation is higher and peaks earlier in PA than in NA donors. We investigated the immunological mechanisms that could underlie these differences. We found that both PA and NA have memory responses to peanut, but the frequency of peanut-specific T cells is higher in PA than in NA. Facilitated antigen presentation could cause both the higher proliferation and precursor frequency in PA. Facilitated antigen presentation activity in vitro was confirmed by showing that IgE depletion decreases proliferation, while adding IgE back restores it.

CONCLUSION

Our results identify FAP as a mechanism that underlies higher responses to peanut in PA. In these individuals, high levels of peanut-specific IgE could furthermore maintain long-term allergic T-cell responses. We raise the question whether, in the future, therapies targeting IgE such as anti-IgE antibodies may be used to suppress these T-cell responses.

Correlation of allergen-specific IgG subclass antibodies and T lymphocyte cytokine responses in children with multiple food allergies

Cytokines can affect the quantity and class of allergen-specific immunoglobulins through the T cell polarization that accompanies atopy. Antigen-specific IgG subclasses and IgE antibodies were compared with intracellular T cell cytokine changes to sensitizing antigens in 23 children with multiple food allergies and 20 healthy controls. Allergic children showed higher levels of total and food-specific IgE, IgG1 and IgG4 to peanut, milk and egg than non-atopic children or adults, coinciding with a TH2 cytokine response to sensitizing antigens. IgG1 and IgG4 antibodies specific to milk and egg and peanut protein were elevated relative to age-matched healthy children (p <or= 0.05) and, in milk- and egg-sensitized children, correlated with cytokine responses (p < 0.05). Peanut-sensitized children additionally had elevated levels of IgG2 and IgG3 also which correlated inversely (p < 0.003 and p < 0.04, respectively) with IFNgamma production. Elevated allergen-specific IgG subclass antibodies in sensitized children correlated with total IgE levels (p <or= 0.05) in all three food allergen groups. The ratio of specific IgG1 to IgG4 was highest in those with high IgE, inverted with resolution of allergy, and correlated with total IgE levels (p <or= 0.01) in milk- and egg-sensitized children. The correlation of TH2 responses with allergen-specific antibodies would implicate polarized T cells in food allergic children in IgE hypersensitivity and overproduction of particular IgG subclasses alike. IgG1:IgG4 ratio declines with allergy sensitization and may denote emerging tolerance.

T cell responses to major peanut allergens in children with and without peanut allergy

BACKGROUND

T cell responses involved in peanut allergy are poorly understood.

OBJECTIVE

To investigate T cell responses towards major peanut allergens in peanut-allergic (PA) subjects compared with peanut-sensitized (PS) non-allergic children and non-atopic (NA) controls.

METHODS

Eighteen PA children, seven non-allergic PS children and 11 NA adults were included. Peripheral blood mononuclear cells were stimulated with a crude peanut extract (CPE). Short-term T cell lines were generated and subsequently stimulated with CPE and purified Ara h 1, Ara h 2, Ara h 3 and Ara h 6. The proliferation and production of IL-13, IFN-gamma, IL-10 and TNF-alpha were analysed.

RESULTS

Proliferation to CPE and major allergens was enhanced in PA subjects. The primary response to CPE was comparable with PS subjects, with increased production of IL-13 and IFN-gamma compared with NA. Production of IL-10 was not observed. In short-term T cell lines, the response to CPE was stronger in PA than in PS and NA subjects. Only PA children had a detectable response to major peanut allergens, characterized by IL-13 production. The response was the highest after Ara h 3 stimulation, and the lowest after Ara h 2 stimulation. No significant correlation was observed between peanut-specific IgE levels and T cell responses to CPE.

CONCLUSION

T cell responses to CPE in PA and PS children were characterized by Th1 and Th2 cytokines. Only PA children showed enhanced Th2 responses to Ara h 1, Ara h 3 and Ara h 6.

Characterization of lymphocyte responses to peanuts in normal children, peanut-allergic children, and allergic children who acquired tolerance to peanuts

Comparing lymphocyte responses to allergenic and nonallergenic foods could reveal the differences between pathogenic and normal immune responses to foods. Defining the cytokine-producing phenotypes of peanut-specific lymphocytes from peanut-allergic children, children who outgrew peanut allergy, and children who have always tolerated peanuts may be useful for understanding the mechanisms of food tolerance. Investigating immune responses against foods is hindered, however, by the fact that circulating food antigen-specific lymphocytes are very rare. In a novel approach we used carboxyfluorescein succinimidyl ester to detect peanut-specific lymphocytes by flow cytometry. We confirmed that these cells are indeed peanut specific by cloning. Peanut-allergic donors show Th2 polarization of cytokine production by peanut-specific cells (IFN-gamma (low), TNF-alpha (low), IL-4 (high), IL-5 (high), IL-13 (high)). Conversely, nonallergic children and children who have outgrown their allergy show Th1 skewing to peanut antigens (IFN-gamma(high), TNF-alpha (high), IL-4 (low), IL-5 (low), IL-13(low)), similarly to nonallergenic food antigens (beta-lactoglobulin, OVA). This finding suggests that peanut antigens do not intrinsically induce Th2 skewing, but that the type of response depends upon the donor's allergic status. In conclusion, food allergic status is characterized by a Th2 response whereas Th1-skewed responses underlie oral tolerance.

Polymorphism in the STAT6 gene encodes risk for nut allergy

Nut allergy is an important and potentially life threatening food allergy with a prevalence of one in 150 children in the UK population. STAT6 (signal transducer and activator of transcription) is an important molecule in the induction and regulation of an allergic response, which maps to chromosome 12q in a region previously linked with total serum IgE concentration and atopy in different populations. We have examined the frequency of a single nucleotide polymorphism (SNP) in the 3'UTR region of STAT6 gene in 71 UK Caucasoid patients diagnosed with nut allergy and 45 atopic patients without nut allergy using PCR-RFLP and compared these with 184 UK healthy controls. The STAT6 G allele frequency was significantly increased in nut allergy patients compared with blood donor controls (P < 0.0001, OR = 2.9, 95% CI: 1.7-4.9), which was under a recessive model (GG vs GA+AA, P = 0.0001, OR = 3.2, 95% CI: 1.7-5.8) but not in atopic patients without nut allergy. The G allele was most frequent in the severe cases and GG homozygosity was associated with the increased risk of severe reaction (OR = 3.9, 95% CI: 1.9-8.3). We conclude that STAT6 3'UTR polymorphism is associated with susceptibility and severity in nut allergic patients in our population.

Modification of T-cell receptor Vbeta repertoire in response to allergen stimulation in peanut allergy

BACKGROUND

Peanut is one of the most common foods causing allergic reactions and is the most common cause of fatal and near-fatal food-related anaphylaxis. Little is known of the immunologic mechanisms that underlie peanut allergy.

OBJECTIVES

In this study we examined clonality of the T-cell response (TCR) to peanut in MHC class II identical, peanut allergy-discordant sibling pairs.

METHODS

Four sibling pairs were investigated. The TCR repertoire was analyzed before and after in vitro stimulation of PBMCs with crude peanut or PHA, as control for general/nonspecific reactivity. Eighteen TCR-Vbeta families were examined by flow cytometry. Where significant differences in incidence of particular TCR-Vbeta families were observed, PCR familyspecific cDNA amplification and gene scanning were performed.

RESULTS

After stimulation with peanut, no selective expansion of any TCR-Vbeta subpopulation was observed with flow cytometry, in either the peanut-allergic or nonallergic siblings, with the exception of 1 peanut-allergic subject who demonstrated a significant increase of TCR-Vbeta11(+) cells (0.3%-5.9% of the total CD3(+) cells). However, gene scanning revealed predominant single-size PCR products for TCRBV11 in all peanut-allergic subjects after peanut stimulation. TCRBV11 polyclo-nality was observed in allergic and nonallergic subjects before peanut stimulation and in nonallergic subjects after peanut stimulation. In comparison, all subjects, before and after stimulation with peanut, showed polyclonality for TCRBV2.

CONCLUSIONS

Our results argue for clonal or oligoclonal TCRs to crude peanut and indicate that changes in the TCRBV11 subpopulation are restricted to peanut-allergic subjects after stimulation with crude peanut allergen.