Patterns of immunoglobulin G responses to egg and peanut allergens are distinct: ovalbumin-specific immunoglobulin responses are ubiquitous, but peanut-specific immunoglobulin responses are up-regulated in peanut allergy

BACKGROUND

The clinical significance of food-specific IgG subclasses in food allergy and tolerance remains unclear. Specific IgG titres are often reported in non-standardized units, which do not allow comparisons between studies or allergens.

OBJECTIVE

To quantify, in absolute units, ovalbumin (OVA)- and peanut-specific IgG levels in children with peanut or egg allergy (active or resolved) and in non-allergic controls. Methods Children aged 1-15 years were recruited. Peanut allergy was diagnosed by convincing history and a 95% predictive level of specific IgE; egg allergy or resolution was confirmed by oral challenge. Serum IgG, IgG1 and IgG4 levels (microg/mL) to OVA and peanut extract were quantified by ELISA.

RESULTS

OVA- and peanut-specific IgG was detected in all subjects. In non-allergic controls (n=18), OVA-specific IgG levels were significantly higher than peanut-specific IgG (median microg/mL IgG=15.9 vs. 2.2, IgG1=1.3 vs. 0.6, IgG4=7.9 vs. 0.7; P<0.01). There were no differences in OVA-specific IgG, IgG1 and IgG4 between egg-allergic (n=40), egg-resolved (n=22) and control (n=18) subjects. In contrast, peanut-specific IgG (median microg/mL IgG=17.0, IgG1=3.3, IgG4=5.2) were significantly higher in peanut-allergic subjects (n=59) compared with controls and with non-peanut-sensitized but egg-allergic subjects (n=26). Overall, the range of IgG4 was greater than IgG1, and IgG4 was the dominant subclass in >60% of all subjects.

CONCLUSION

OVA-specific IgG levels of egg-allergic, egg-resolved or control groups are not distinguishable. Higher peanut-specific IgG levels are associated with clinical allergy, but the range of IgG titres of the allergic and control groups overlapped. Hence, OVA and peanut-specific IgG measurements do not appear to be of diagnostic value. Strong IgG responses to OVA may be a normal physiological response to a protein frequently ingested from infancy, whereas up-regulated IgG responses in peanut allergy may be indicative of a dysregulated immune response to peanut allergens.

Humoral and cellular responses to cow milk proteins in patients with milk-induced IgE-mediated and non-IgE-mediated disorders

BACKGROUND

Cow milk allergy (CMA) is one of the most common food allergies in childhood. Patients with CMA present with a wide range of immunoglobulin (Ig)E- and non-IgE-mediated clinical syndromes. Limited information is known about the specific humoral and cellular responses to cow milk proteins in these various forms of CMA.

OBJECTIVE

The aim of the study was to determine IgE, IgA, IgG1 and IgG4 antibody levels and lymphocyte proliferative responses to the major cow milk allergens in patients with IgE- and non-IgE-mediated CMA.

METHODS

One hundred and forty cow milk allergic patients, 6 months to 22 years of age, were included in the study. One hundred and thirteen patients had IgE-mediated CMA, 11 had milk protein-induced enterocolitis syndrome and 16 had allergic eosinophilic gastroenteritis. Twenty-one patients without food allergy, 8 months to 18 years of age, served as controls. Serum IgE, IgA, IgG1 and IgG4 antibodies to alpha-, beta-, and kappa-casein, alpha-lactalbumin and beta-lactoglobulin were measured using enzyme-linked immunosorbent assays. For a subset of these patients, we performed lymphocyte proliferation assays to the various milk allergens.

RESULTS

Patients with IgE-mediated CMA had higher specific IgE concentrations to casein compared with whey proteins (P < 0.001). In this group of patients, there was a positive correlation between IgE levels and levels of the other isotypes for all four milk proteins (P < 0.001). In general, the caseins were the more allergenic and antigenic proteins in all groups of patients. Patients with enterocolitis syndrome produced less milk protein-specific IgG4 (P < 0.05) and had a trend for higher IgA antibody levels when compared to the control group. Lymphocyte proliferative responses in all groups with CMA were significantly higher than controls (P < 0.05), although this response was similar in patients with IgE- and non-IgE-mediated CMA.

CONCLUSION

There is a distinct pattern of humoral antibody response in the different forms of CMA. Patients with IgE-mediated CMA have an elevated polyisotypic response to cow milk protein. The relative lack of specific IgG4 production in patients with enterocolitis syndrome may be involved in the pathogenesis of the disease. In general, caseins appear to be the predominant allergen in patients with CMA.

A novel model of sensitization and oral tolerance to peanut protein

The prevalence of food allergic diseases is rising and poses an increasing clinical problem. Peanut allergy affects around 1% of the population and is a common food allergy associated with severe clinical manifestations. The exact route of primary sensitization is unknown although the gastrointestinal immune system is likely to play an important role. Exposure of the gastrointestinal tract to soluble antigens normally leads to a state of antigen-specific systemic hyporesponsiveness (oral tolerance). A deviation from this process is thought to be responsible for food-allergic diseases. In this study, we have developed a murine model to investigate immunoregulatory processes after ingestion of peanut protein and compared this to a model of oral tolerance to chicken egg ovalbumin (OVA). We demonstrate that oral tolerance induction is highly dose dependent and differs for the allergenic proteins peanut and OVA. Tolerance to peanut requires a significantly higher oral dose than tolerance to OVA. Low doses of peanut are more likely to induce oral sensitization and increased production of interleukin-4 and specific immunoglobulin E upon challenge. When tolerance is induced both T helper 1 and 2 responses are suppressed. These results show that oral tolerance to peanut can be induced experimentally but that peanut proteins have a potent sensitizing effect. This model can now be used to define regulatory mechanisms following oral exposure to allergenic proteins on local, mucosal and systemic immunity and to investigate the immunomodulating effects of non-oral routes of allergen exposure on the development of allergic sensitization to peanut and other food allergens.

Mixed antibody and T cell responses to peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 in an oral sensitization model

BACKGROUND

Peanut allergy is known for its severity and persistence through life. Several peanut proteins have been identified as allergenic and are indicated as Ara h 1-7. Very little is known about the mechanisms that underlie sensitization to peanut proteins.

OBJECTIVE

The purpose of the present study was to reveal the immune responses that are induced against peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 during sensitization, including the very early responses.

METHODS

Humoral and T cell responses against peanut and the peanut allergens were examined in an early and later stage of sensitization in an established murine model of peanut anaphylaxis. Therefore C3H/HeJ mice were orally exposed to two different doses of peanut extract plus cholera toxin.

RESULTS

Oral sensitization to peanut was characterized by an antigen-induced mixed cytokine response in the spleen (IL-4, IL-5, IL-10 and IFN-gamma), which could already be observed 7 days after the onset of exposure. Additionally, polyisotypic humoral responses (IgE, IgG1 and IgG2a) against peanut were found in the serum. Moreover, we demonstrated that these T helper (Th)1/Th2 cytokine and antibody responses were also directed specifically against the major peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6.

CONCLUSIONS

This study implicates that both Th1 and Th2 phenomena are involved in the development of peanut allergy in the C3H/HeJ murine model. Furthermore, we show that the present oral model is suitable to examine immune responses to food allergens during different stages of sensitization upon treatment with a whole food extract.