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

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 A x 30 A. 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 A and the dimensions of subunits protruding from the centre were 50 to 55 A x 20 A.