The ultrastructure of Australia antigen in the presence and the absence of specific antibodies.

The technical conditions which allow high resolution electron microscopy of Australia (AU) antigen have been investigated. It was found that uranyl acetate, used as a negative stain, provided reliable and consistent results. AU antigen may have a tubular or two round forms, the dimensions of which are reported. Evidence is presented which suggests that the round forms derive from the tubular forms. In the absence of added antibody AU antigen appears to consist of subunits, regularly arranged in a helical lattice. After reaction with specific antibody the geometry of the lattice is less evident or even totally obscured due to the presence of material attached to the particle surface. It has been shown that this material consists of antibody molecules having the dimensions and shape typical of IgG. At higher antibody concentrations, clumps of antigen particles are formed. It is suggested that the changes in the elementary structure be used as a marker for the presence of a reaction between AU antigen and antibody. The formation of clumps is considered to be a less reliable marker because of the occurrence of nonspecific agglutination of particles with the negative staining procedure. AU antigen particles prepared from the sera of patients suffering from chronic hepatitis were found to have antibody attached to their surface. Whether this finding is a typical feature of this liver disease or merely an occasional observation, is not clear at present.