ELISA Method for Quantitative Measurement of IgA and IgG Specific Anti-gliadin Antibodies

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Abstract
In this study we describe the application of an enzyme-linked immunosorbent assay (ELISA) for the measurement of anti-alpha-gliadin antibodies (AGA) in absolute units (microgram protein/ml). Enriched samples of IgA and IgG AGA were obtained by means of protein A chromatography after immunoaffinity purification of pooled sera from untreated celiac patients. No cross-reactivity with other food antigens (beta-lactalbumin, soya proteins, ovalbumin) was detected. The quantitative evaluation of protein content in IgA and IgG AGA samples obtained by immunoaffinity chromatography, was performed by means of ELISA sandwich method using a reference curve obtained with pure standard human immunoglobulins. Scalar concentrations of purified IgA and IgG were then used to obtain a reference standard curve by means of an ELISA method. Such standard curve was utilized for titrating AGA in 214 sample sera. The minimal detectable concentration of IgA and IgG AGA was 0.02 micrograms/ml. The reproducibility of within- and between-assay resulted very good for IgA-AGA and acceptable for IgG-AGA. The method here described seems to be satisfactory not only for quantitative diagnostic purposes in routine screenings but also in epidemiological studies. Moreover, it can constitute a suitable way to solve practical problems of quality control of AGA ELISA assay.

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