Immunoconglutinins in human saliva--a group of unusual IgA antibodies.

It has been found that most normal human salivas contain high titres of immunoconglutinin activity (antibody to bound complement components). These salivary immunoconglutinins (IKs) have been found to show highly unusual properties. Thus the activity is dependent on calcium ions and readily reversible by EDTA. On the basis of this property the salivary IKs have been substantially purified by absorption and elution from antigen—antibody—complement complexes. EDTA-reversibility is a characteristic property of bovine conglutinin but the salivary factors in all other ways behave as immunoconglutinins rather than conglutinin. The activity is also uncharacteristically readily inhibited by the presence of free serum. Antigenically the salivary IKs appear to be IgA but their sedimentation coefficient is greater than 19S even in molar acetic acid. The origin and function of these salivary factors is unclear. IgA antibodies are generally believed not to fix complement, nor is whole complement activity present in saliva, so there is unlikely to be a good local antigenic stimulus. It may be that they represent antibodies to cross-reacting antigens.