Failure of rabbit anti-Streptococcus mutans serum to penetrate in vitro plaque

An indirect fluorescent antibody technique indicated that specific antiserums did not penetrate in vitro plaque formed by Streptococcus mutans. Specific reactions did occur between the antiserums and antigens in the surface layers of plaque globules. Measurements of plaque diameters indicated that the serums exerted a nonspecific effect of enhancing plaque growth.