Background
Along with the recent development of diagnostic techniques it has become increasingly popular to use serum concentration levels of specific IgG (sIgG) and IgG
4 (sIgG
4) as markers of food hypersensitivity. Vast popularity of these diagnostically incorrect tests provoked EAACI to issue an official statement which was later supported by AAAAI and CSACI [
1‐
3]. Scientific associations do not recommend using sIgG and sIgG
4 assays in the food hypersensitivity diagnostics. They point out that many individuals have their elevated levels which do not correspond to clinical symptoms of the disease. The research has shown that in humans the presence of food sIgG and sIgG
4 is highly individual. The sIgG appear in half of the population, usually as a response to the most common foods [
4]. The sIgG
4 is only in the case of some food allergens of cow’s milk and egg protein. It has not been resolved so far why in healthy people the frequency and the titers of food sIgG and sIgG
4 show such substantial individual variations. Does it depend merely on the frequency of food consumption and the nature of the antigen? Or are there any additional factors?
In this paper we make a hypothesis that these factors can be gastrointestinal inflammatory diseases. One of them is coeliac disease (CD) which can be asymptomatic [
5]. The adults with untreated CD showed higher sIgG activity for gliadin, casein and ovalbumin [
6,
7]. There have been no research in this respect into other gastrointestinal diseases, hence the question arises if in their case the titers of food sIgG and sIgG
4 are different from normal. Some of these diseases, e.g. the infection with Helicobacter pylori (HP), are very common and can take a non-symptomatic or mildly symptomatic form or its symptoms may be non-specific.
The purpose of this paper is a comparative analysis of the frequency and titers of wheat and rice sIgG and sIgG4 in healthy children and the children with IgE-mediated wheat allergy (WA), with CD and HP. Moreover, we evaluate the usefulness of assays of wheat sIgG and sIgG4 in the WA diagnostics. Although wheat is one of the most common food allergens in children, the presence of food sIgG and sIgG4 in WA has’nt been discussed in the literature.
Methods
We compared 338 assays each of wheat and rice sIgG and sIgG
4 antibodies determined in 200 children in four groups: 50 children with WA (50 assays each at the time of diagnosis and during the elimination diet; 38 assays during the tolerance); 50 children with CD (diagnosis – aCD, remission - rCD), 50 children with HP and 50 children from the control group (Table
1). Information was collected about the subjects’ consumption of wheat and rice (a questionnaire). The course of WA in a group of 50 children described in this paper (clinical picture over the years, tolerance development age and its factors, specific IgE and IgE on diagnosis, during diet treatment and tolerance) were specified earlier in References #8.
Table 1
Characteristics of the study patients
Control group | 50 | 26 | 66,4 | 12 – 197 |
Wheat allergy | | | | |
-Diagnosis -Diet treatment -Tolerance | 50 50 38 | 32 32 20 | 13,0 36,0 69,5 | 2 – 22 21 – 42 37 – 192 |
Coeliac disease | | | | |
-Active -Remission | 50 50 | 19 19 | 76,3 98,6 | 33 – 230 57 – 254 |
Helicobacter pylori infection | 50 | 23 | 97,4 | 58 – 212 |
WA was diagnosed in children with positive food challenge results (double-blind placebo-controlled food challenge, DBPCFC) with symptoms occurring within 2 h after wheat consumption and positive SPT as well as with the levels of wheat sIgE higher than 0.7 kU/L. The first challenge test was performed as the open food challenge (OFC), the second - always as the DBPCFC followed by the OFCs. DBPCFC has been described in detail before [
8]. 38 children developed tolerance. The subjects were diagnosed with other food allergies, most frequently to cow’s milk, egg protein and peanuts. During the observation the majority of children were diagnosed with atopic dermatitis (78 %), asthma (48 %) and allergic rhinitis (34 %). The progress of WA has been described in detail in References #8. The sIgG and sIgG
4 assays were made at the time of diagnosis (the median age was 13 months: 2–22 months.), after 2 years of treatment with a wheat-free diet (the median age was 36 months: 21–42 months.) and during the period of tolerance - negative OFC with wheat (the median age was 69.5 months: 37–192 months).
CD children were examined at the time of diagnosis – aCD (76.3 months: 33 – 230 month.) and remission – rCD (98.6 months: 57 – 254 months). The aCD was made for children with the malabsorption syndrome (Marsh IIIC) and with antibodies to tissue transglutaminase as well as with endomysial antibodies [
5]. The rCD was diagnosed when this antibodies were normal. The sIgG and sIgG
4 assays were not made until after 12 monthsnths of remission, usually 2 years after the diagnosis.
HP was diagnosed in children (97.4 months: 58 – 212 mo.) with typical endoscopic (gastritis, positive CLO test) and histological picture (chronic gastritis) [
9].
The control group (66.4 months: 12 – 197 months.) was composed of patients in whom lesions in the upper part of the digestive tract were ruled out (endoscopic and histological examination). Children had been admitted due to abdominal pains or dwarfism (suspected malabsorption syndrome). They were diagnosed with functional gastrointestinal disorders or constitutional dwarfism.
The inclusion criteria were: diagnosed WA, CD or HP infection and the consent of participants and their guardians.
The criteria for a child to be excluded from observation were other chronic diseases and decreased concentration of total IgG. For children from the CD group, the HP group and the control group an additional elimination factor was atopy which was diagnosed on the basis of an elevated level of tIgE and/or positive sIgE test results for 8 allergens (milk, egg, peanut, cat, Cladosporium herbarum, Dermathophagoides pteronyssinus, grass, sagebrush) and/or a positive SPT (10 air-borne and 10 food allergens). 56 children were lost to follow-up: 52 children with atopy and from WA group: 1 child with ulcerative colitis and 3 children who visited the clinic only once.
All the patients remained under the care of an attending physician (an allergologist or gastroenterologist) throughout the whole observation period. Children were patients of the outpatient clinic and the gastroenterology department. The study was conducted from January 1990 to May 2012.
The titers of tIgE (accuracy 2–9,1 %, sensitivity <2 kU/L, specificity 100 %), sIgE (accuracy 5–11 %, sensitivity <0,35 kU/L, specificity 100 %), sIgG (accuracy 5–10 %, sensitivity <20ug/L, specificity 100 %) and sIgG4 (accuracy 4–7 %, sensitivity <1,5ug/L, specificity >95 %) to wheat and rice were determined by means the FEIA method using the ImmunoCAP System (UniCAP, CAP 100; Pharmacia & Upjohn Diagnostics AB, Uppsala, Sweden). SPTs were performed by means of commercial solutions manufactured by Allergopharma (Germany). The wheal reactions were read after 15 min. (histamine) - 20 min (allergens). Tests were considered positive when the wheal size was ≥ 3 mm in diameter in comparison with the negative control (control solution).
The data were characterized by the median, the minimum and maximum values. The Mann–Whitney test was used to compare sIgG and sIgG4 levels among the patients in the examined groups. The correlation between the selected variables was evaluated with the Spearman rank correlation. A tool used for the statistical analysis was STATA 11, License No 30110532736.
The study was conducted in compliance with the Declaration of Helsinki and following the consent by the Ethical Committee of the Pomeranian Medical University in Szczecin (BN-001/107/90). Sources of funding for the research: State Committee for Scientific Research grant No4 PO5E 086 14 and the clinic in-house research budget.
Discussion
In our study we examined the frequency and titers of wheat and rice IgG and IgG
4. We compared a group children not suffering from atopy and gastrointestinal diseases in the upper part of the digestive tract (control group) to a group of children with WA and with CD and HP, two common and usually mildly symptomatic gastrointestinal diseases. Atopy had been excluded from the study since it is known to predispose to developing food sIgG and sIgG
4 [
7,
10,
11].
Wheat and rice sIgG are not present in all healthy children (control group) but are more common in children with wheat allergy, coeliac disease and Helicobacter pylori infection
The results confirm other authors’ observation that food sIgG do not develop in all healthy children. In addition to that, their incidence and titers vary depending on the food [
4]. In this study we detected double as much wheat sIgG as rice IgG (66 % and 30 %) (Table
2). Our research has also shown that wheat sIgG reach higher titers than the ones that are rice specific. In children with WA, CD and HP not only did we observe more common wheat and rice sIgG, but they also reached higher concentration levels in serum (Figs.
1,
3). We did not find the wheat and rice sIgG
4 fraction in children from the control group who suffered neither from atopy nor from any gastrointestinal disease (Table
2). The fraction was present in children from the remaining groups: WA, CD and HP (Figs.
2,
4).
The highest concentrations and frequency of wheat and rice sIgG were observed in aCD, while in rCD their frequency was lower and their titer values were smaller (Fig.
2).
Wheat and rice IgG4 don’t present in healthy children (control group) but are more common in children with wheat allergy, coeliac disease and Helicobacter pylori infection (Table 2)
The results confirm other authors’ observation that food IgG
4 do not develop in healthy children as a reaction to all kinds of food. As a prevailing subclass they are synthesized for some food allergens only, mainly to chicken egg protein and cow’s milk. They are most common and reach the highest titers for the chicken egg protein ovomucoid, while in the case of cow’s milk casein, gliadin and gluten the system first of all synthesizes subclasses 1 and 3 of immunoglobulin G [
6].
Wheat sIgG and sIgG4 do not correlate with the wheat allergy clinical picture
In the majority of children with WA and CD the humoral response to wheat in the class sIgG and sIgG
4 was persistent – specific antibodies were present in serum even after wheat had been eliminated from the diet. In WA they were still found in most of the subjects, sIgG titer did not change and sIgG
4 decreased (
p < .05). In rCD their concentration fell considerably. Persisting long-term highly stable sIgE and sIgG
4 epitope-binding patterns were also observed among patients with peanut allergy who were avoiding the allergen [
12,
13].
In contrast to children with WA, the elimination of a food from healthy children’s diet results in decreased sIgG titers [
14]. Also in milk allergic small children being on a milk-free diet a considerable fall in sIgG serum concentration was observed, which had taken place before their tolerance to milk was developed [
15,
16]. Infants with longstanding presence of milk or hen’s egg sIgG suffered from a persistent allergy to those foods [
17].
We also found out that the frequency and titers of wheat sIgG and sIgG
4 did not correlate to the WA clinical picture. They were developed by the majority of children, but not in all of them, and their frequency was the same in all the disease phases (Table
2). Rice sIgG was observed in the majority of children in all the WA phases, while rice sIgG
4 - in a half of the subjects. This indicates that in WA the immune response is changed. It refers not only to food allergens, but also to tolerated foods.
However, several opposite findings have been published that the sIgG and sIgG
4 titers do not differ between healthy individuals and patients with atopy or with food allergy to cow’s milk, chicken’s egg and kiwi [
16,
18,
19]. Tay et al. found that serum concentration of ovalbumin sIgG and sIgG
4 is identical in healthy, allergic and tolerant individuals, but in the case of peanut sIgG and sIgG
4 the titers are higher in allergic and atopic patients than in healthy subjects [
10].
It is generally assumed that in children with food allergy the elevated titers of food sIgG are the effect of their increased intestinal permeability. When an allergen is eliminated from a diet, intestinal permeability normalizes [
20]. In our study group, most of the WA children (78 %) suffered from atopic dermatitis as well. As Majamaa and Isolauri have found out, in such patients the transport of food macromolecules is seven times larger than in healthy individuals and it includes 20 % of the absorbed proteins [
21,
22].
The development of food tolerance, both natural and in oral immunotherapy, is associated with the increase in food sIgG
4 [
23‐
26]. The maintenance of tolerance to cow’s milk in atopic individuals is characterized by the fall in sIgE titers and high levels of sIgG
4 [
27]. Children with egg allergy who have developed tolerance to baked egg also experience lowered sIgE and elevated sIgG
4 concentrations [
28]. Low titers of sIgG
4 in young children with food allergy indicate its longstanding character. High serum concentrations of sIgG
4 is characteristic to these food allergic children who develop their tolerance early [
29,
30]. Sletten et al. claimed opposite findings that in children with milk allergy high titers of sIgG
4 for milk allergens decrease during the tolerance period [
31].
In conclusion, the incidence and titers of sIgG and sIgG4 are determined not only by the type of food, but also by the type and the activity of a gastrointestinal disease. Higher incidence and titers of food sIgG and sIgG4 were observed in all the diseases under study, i.e. in WA, CD and HP. This indicates that gastrointestinal diseases, due to its commonness and mildly-symptomatic nature, can be one of the factors responsible for high individual versatility of food sIgG and sIgG4.
The highest concentration of wheat and rice sIgG are in children with coeliac disease
High concentrations of food sIgG in serum are characteristic of CD (Fig.
3). They are elevated also at the time of remission when they reach slightly higher titers than in HP infection. Elevated sIgG
4 is not a distinctive feature of CD as it is secondary to the rise in sIgG. Still, in CD these antibodies reach top values that are just slightly lower than in WA where the wheat sIgG
4 synthesis is preferential (Figs.
2,
4). What is more, it is worth noting that in WA and CD the enhanced synthesis of sIgG and sIgG
4 includes not only the symptom-inducing food (wheat), but also the food which is tolerated (rice). This confirms that in WA, CD and HP the immune response to various foods is changed.
Wheat sIgG and sIgG4 are useless in the wheat allergy diagnostics
The findings of our study also point to the fact that the assays of wheat sIgG and sIgG4 are useless in the WA diagnostics. In WA the concentration of these antibodies increases as a response to not only wheat, but to other foods as well, hence it is impossible to determine the actual allergen. The elevated titers persist throughout all the disease phases, so patients recently diagnosed for allergy cannot be distinguished from those who are being treated with elimination diet or have entered the period of tolerance.
The above findings are burdened by a small size of the sample (50 children in each of the groups). Therefore, it is necessary to confirm the findings in a larger group of patients.
Competing interests
The authors declare that they have no competing interests.
All the authors have no financial relationships relevant to this article to disclose.
Authors’ contributions
GC-B conceptualized and designed the study, designed the data collection instruments, coordinated and supervised data collection, drafted the initial manuscript, and approved the final manuscript as submitted. MB conceptualized the study, supervised data collection, carried out the analyses, drafted the initial manuscript and approved the final manuscript as submitted. AG conceptualized the study, data collection, carried out the analyses, drafted the initial manuscript and approved the final manuscript as submitted.
Grażyna Czaja-Bulsa – Prof Pomeranian Medical University in Szczecin, Poland
- paediatrician, allergologist, gastroenterologist
- head of Pediatrics and Pediatric Nursery Unit of The Pomeranian Medical University
- head of Division of Paediatrics, Gastroenterology and Rheumatology of The „Zdroje” Hospital
Michał Bulsa – MD
Aneta Gębala – MD, PhD, paediatrician, gastroenterologist