A Sensitive Method for Specific Quantitation of Secretory IgA

A method to quantitate specifically secretory IgA (SIgA) has been developed using the enzyme-linked immunosorbent assay. The IgA in the test sample was adsorbed to anti-alpha antibodies attached to plastic tubes via a cost of IgA myeloma protein. The reacted SIgA was determined using anti-secretory component antiserum conjugated with alkaline phosphatase. The technique permitted quantitation of secretory IgA in biological fluids like milk, urine, and saliva with a reproducibility of +/-7%, down to 0.03 mg/l. In contrast to earlier techniques, the presence of up to 157% of serum IgA without secretory component (SC) and free SC did not disturb the measurements of SIgA. Furthermore, variations in pH and osmolarity, within biological ranges in secretions, did not influence the estimations.