Effect of in vitro treatment with reducing drugs on structure and function of human secretory immunoglobulin A

Samples of unstimulated whole saliva from 15 healthy children with 0.5--6 mg/100 ml of secretory IgA and from 10 healthy adults with 4--18 mg/100 ml of secretory IgA were pooled and treated in vitro with dithiothreitol and alpha-mercaptopropionylglycine. The effect of these reducing drugs on the immunochemical properties of secretory IgA was evaluated. Dithiothreitol induced depolymerization of secretory IgA and splitting of the secretory piece from the IgA molecule; furthermore it strongly reduced the titer of secretory antibodies to Escherichia coli antigens. The drug alpha-mercaptopropionylglycine apparently did not affect either the polymeric structure of secretory IgA or the titer of secretory anti-E. coli antibodies; however it induced splitting of the secretory piece. On the whole it appers that drugs with reducing properties, currently employed for liquifying mucous secretions in clinical practice, should be carefully evaluated for possible depressive side-effects on local immunity.