Prozone Effects in Indirect Immunofluorescence

A marked prozone effect was observed in indirect immunofluorescence (IFL) with rabbit antisera against rat renal proximal tubular epithelial brush border (BB) antigens: anti-BB antibodies were not detectable if used in high concentrations but were readily demonstrated if sufficiently diluted. The prozone effect occurred in spite of demonstrated binding of anti-BB antibodies to target antigens. No prozone was seen when direct IFL was used, and 'cross-reacting' antigens in small-intestinal epithelial brush border were detectable by indirect IFL without prozone. It was concluded that the anti-immunoglobulin conjugates were unable to reach antigenic determinants on tightly clustered immunoglobulin molecules. Thus prozone effects seem to depend primarily on the density of antigen determinants in the target tissues.