An enzyme-linked immunosorbent assay for human secretory immunoglobulin A in parotid saliva

An enzyme-linked immunosorbent assay (ELISA), based on the double antibody sandwich method, was developed to quantify human secretory immunoglobulin A (sIgA) in saliva samples obtained from the parotid gland. The system consisted in: coating antibody (anti-IgA) at 2.5 micrograms/mL, enzyme-antibody conjugate (anti-IgA-SC-HRP) at 1/40,000 dilution in a 15 min enzyme-substrate reaction. Standard curves, prepared with sIgA purified from human colostrum, were consistently linear from 10 to 2500 ng/mL, which represents the sensitivity and saturation limits of the assay, respectively. This assay has a reproducibility ranging from 12% to 20% with samples of different concentration of sIgA, and an accuracy ranging from 95.7% to 106.7%, compared to radial immunodiffusion (RID). This system was specific for sIgA, since no reaction occurred with exogenously added human purified IgG, IgM or albumin, nor with the proteins in the detection system. The main features of this ELISA are: a) it is highly specific and sensitive for sIgA; b) quantitation of sIgA in parotid saliva samples can be made in relatively short time (4 to 5 hours); c) many samples can be run per microplate; d) it can be adapted to almost any clinical laboratory at reasonable costs and e) it is suitable for automatization. On the other hand, parotid saliva is an easy-to obtain sample using the Curby device and represents a non-invasive method causing minimum discomfort to subjects. The use of this type of samples, together with this ELISA, would allow large-scale screening of sIgA levels, both in normal and diseased populations.