Measurement of faecal immunoglobulin a levels in young children

A nephelometric immunoassay was developed to quantify immunoglobulin A (IgA) in children's stools. This method enables IgA in faecal protein extracts to be measured over a large range of concentrations (1.61-51.50 mg/L) with good accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation (CVs) of 1-6%). An excellent recovery (105%) was obtained in stool samples overloaded by purified colostral IgA, demonstrating that the method used for faecal IgA extraction is adapted, not to induce significant IgA degradation, and probably allow a complete extraction of IgA. The amount of faecal IgA, as determined in stool samples from 125 children (6-24 months old), was an average of 14 mg per 100 g of stools (about 10% of the total protein stool content), with large individual variation (3-30 mg per 100 g of stools). No correlation was observed between faecal IgA amounts and the children's age or sex. Such an immunoassay could enable exhaustive noninvasive investigations of the maturation of the intestinal immune system, as well as accurate studies of the effect of oral dietary supplementation on IgA regulation.