Human serum antibodies specific for secretory IgA.

Human antibodies which react in a haemagglutination system with secretory IgA, but not serum IgA, were found in serum from 14 per cent of normal subjects, 8 per cent of patients with chronic inflammatory bowel diseases and over 50 per cent of subjects with either peptic ulcer or alcoholic cirrhosis. The specificity of these reactions for secretory IgA was confirmed in inhibition experiments using a panel of immunoglobulin proteins. The anti-secretory piece factors in two sera were found by zone electrophoresis and sucrose density gradient experiments to have physical characteristics most compatible with IgG and IgA proteins, respectively. Further characterization of the specificity of these anti-secretory IgA factors, using a panel of colostral IgA proteins from individual mothers and isolated secretory piece, demonstrated a high degree of variability in antigenic specificity for secretory IgA. In three of five sera tested, the reaction was specific for components in isolated secretory piece. Inhibition studies using products of peptic digestion of colostral IgA suggest that secretory piece is attached to the Fc fragment of the molecule and that digestion releases at least some secretory piece molecules relatively intact. Although the significance of these anti-secretory IgA antibodies is presently unknown, it is anticipated that they will be valuable as reagents in further studies on the molecular structure and biology of secretory IgA.