Development and Analytical Evaluation of a Microarray Assay for Quantitative Determination of Human Blood IgG...

Food intolerance mediated by IgG antibodies is an adverse reaction resulting from the difficulty to digest or metabolize a food or food component(s) and is manifested by numerous nonspecific symptoms, potentially also provoking systemic inflammation and allergy symptoms. Consequently, the detection of circulating food-specific IgG has a diagnostic value with possible clinical applications.

We produced microarray chips able to analyse 16 blood samples simultaneously. After validation of the characteristics and performance using stringent quality control criteria, we investigated their diagnostic validity for IgG-mediated intolerance in 6575 subjects from the Italian population to 92 purified food proteins. Moreover, this assay was performed on capillary blood samples collected from the fingertip, permitting a minimally invasive and practical collection of blood.

Sixteen antigens showed an IgG response greater than 10 % and eight aliments of these had a reactivity greater than 15 %. Wheat (20.4 %), cow's milk (30.8 %), brewer's yeast (23.4 %) and mozzarella cheese (22.4 %) produced a very high IgG response, greater than 20 %, probably due to their widespread use in the Italian cuisine. Goat's milk, various milk derivatives (like gorgonzola, Grana Padano and parmesan cheese), durum wheat, kamut, egg and gluten had a reactivity greater than 15 %. Four food antigens (emmer, pecorino cheese, ricotta and rye) caused a moderate IgG reactivity ranging between 10 and 15 %. The other food extracts showed a mean low IgG reactivity below 10 %. No significant differences were observed between female and male subjects or among the various Italian regions analysed. In contrast, the highly reactive food antigens showed a decrease in IgG response with increasing age.

After validation, our microarray chips proved to be a robust method with good reproducibility and low variation. Even if the primary aim of this study is to evaluate the incidence of IgG-mediated reactivity in the Italian population using a novel microarray technology and to compare the results with a previous study conducted using enzyme-linked immunosorbent assay (ELISA), this analytical approach can also help identify the triggers of intolerance symptoms and help doctors or nutritionists in selecting the best treatment for patients, with the additional aim of clarifying the controversy surrounding IgG testing. Finally, our microarray technology enables high throughput, ensuring that a large number of samples can be analysed with significant savings in time, reagent and costs, while remaining minimally invasive for patients.