Human secretory immunoglobulins. VI. Association of free secretory piece with serum IgA in vitro

Abstract

In vitro complexing of native free secretory piece (SP) was relatively specific for serum IgA, but only a minor proportion of the molecules combined. Two types of aggregate with the molecular size of polymer IgA were formed. One was indistinguishable from native secretory IgA; it contained disulphide-linked SP and exhibited a closely packed quaternary structure with inaccessible I determinant. This determinant was exposed in the other type which apparently represented relatively loose complexes stabilized solely by noncovalent forces.