AVIDITY OF IgG ANTIBODIES AGAINST GLIADIN AND β-LACTOGLOBULIN IN FOOD ALLERGY/INTOLERANCE.

Abstract

109 Avidity denotes the overall strength of the interaction between antibody and antigen. The biological effectiveness of an antibody is related to its avidity. Gliadin and β-lactoglobulin (BLG) are trigger antigens in celiac disease and cow's milk protein allergy, respectively. The aim of the present study was to examine the avidity of IgG antibodies against gliadin and BLG in children with and without food allergy/intolerance. Patients: The avidity of IgG anti-gliadin antibodies was analysed in healthy children (n=30, age 7-48 months), celiac children with active disease or in remission (n=21, age 10-43 months). The avidity of IgG anti-BLG antibodies was measured in sera from healthy children (n=33, age 8-48 months), children with celiac disease, active disease or in remission (n=27, age 10-47 months) and children with cow's milk protein allergy manifested as gastrointestinal and/or skin symptoms(n=36, age 3-41 months). Methods: A thiocyanate elution assay was used to determine the relative avidity index (Jones et al., J Immunol Methods 1987; 105: 111-117). IgG antibody levels in sera were determined with ELISA.Results: In healthy children the avidity of IgG serum anti-gliadin antibodies as well as IgG anti-BLG antibodies increased significantly with age(regression analysis, p< 0.05 and p< 0.001, respectively). Such a clear avidity maturation was also found in celiac children, especially in those with active disease. Untreated celiac children showed, adjusted for age, significantly higher avidity of IgG anti-BLG antibodies than healthy children(p< 0.05), whereas children with cow's milk protein allergy displayed an avidity in the same range as the group of healthy children. Celiac children, followed longitudinally with regard to the avidity of their anti-gliadin antibodies, demonstrated a slightly increasing avidity when in remission on gluten-free diet, in parallel, decreasing IgG anti-gliadin antibody levels were found. At relapse after gluten challenge a marked progression of avidity was seen. Thus, the avidity of IgG anti-gliadin antibodies were higher in celiac children at relapse on gluten challenge than in healthy children of the same age (p< 0.03). A significant correlation between avidity and IgG antibody levels against BLG was found in healthy children and patients with cow's milk protein intolerance (r=0.47, p< 0.05 and r=0.51 p< 0.05, respectively). Likewise, healthy children showed a weak positive correlation between avidity and anti-gliadin antibody levels (r=0.35, p< 0.05). No such relationship was found in sera from children with celiac disease.Conclusions: The persistent antigen exposure to gliadin and BLG results in an increasing avidity of corresponding IgG antibodies during the first years of life. The appearance of high-avidity IgG antibodies against gliadin or BLG in cases of celiac disease is possibly the effect of increased permeability due to the enteropathy and/or the inflammatory responseper se. The progressive avidity seen over time may be appropriate, allowing the immune system to deal effectively with these antigens. Additionally, during disease conditions such as celiac disease, high-avidity antibodies might contribute to the disease process participating in complement-mediated lysis or antibody-dependent cell-mediated cytotoxicity(ADCC).