PURIFICATION, ANTIBODY ACTIVITY AND ULTRASTRUCTURE OF SECRETORY AND HIGH‐POLYMER IgA

Abstract

Simple methods for the purification of secretory and high‐polymer serum IgA are described. Gel filtration on exceptionally tall agarose columns was an essential step in these purification procedures. The presence of s‐IgA‐albumin complexes was noted in some colostrum samples. These complexes could be dissociated by mild reduction. Colostral IgA and high‐polymer serum IgA from individuals vaccinated with poliovirus contained virus‐neutralizing antibodies in modest titres. The ultrastructure of secretory IgA resembled a wishbone and the mean dimensions of the molecule were approximately 125 Å x 30 Å. The ultrastructural findings are compatible with a molecular model in which two IgA monomers are superimposed upon each other in a close‐packed state with the secretory piece inserted in the constant region of the α‐chains. The high‐polymer serum IgA studied was made up of four filamentous structures joined at a central point. The total span of the molecule was approximately 100 Å and the dimensions of subunits protruding from the centre were 50 to 55 Å x 20 Å.