Characterisation of the main molecular forms of human fecal immunoglobulin A

The molecular composition of fecal IgA is poorly documented, although it is of theoretical and practical importance to determine the different forms of IgA in faeces. Two main molecular forms were isolated by successive steps of ion-exchange chromatography and gel-filtration. The first consisted of secretory IgA dimers dissociating into slightly lower molecular mass forms under the influence of the electric field during electrophoresis. The other contained cleaved-IgA complexed with alpha 1-antitrypsin, that is considered to be a serum origin marker. These results confirm that secretory IgA are relatively resistant to digestive enzymes in vivo, and suggest that alpha 1-antitrypsin-bound fragments originate from serum IgA monomers. Analysis of the proportions of these forms may be of value in the investigation of gut diseases.