Biological activity of secretory IgA--comparison of agglutinating specificity with SIgA and Ca++-dependent agglutinin--.

Ca++-dependent bacterial agglutinin was isolated from the human parotid saliva by gel filtration of Sepharose 2B. The agglutinin appeared in the void volume fractions. Treatment of this agglutinin with EDTA resulted in the loss of its ability to agglutinate the bacteria. Standardized solutions of the agglutinin were tested for the agglutinating activity against 18 strains of oral indigenous bacteria. It was found that the agglutinin exhibited varying degrees of activity to all the test strains and the activity was generally higher than that of secretory IgA. It was also found that the receptor sites of the Ca++-dependent agglutinin for Str. sanguis and Str. mitis were identical whereas SIgA contained a number of available binding sites, for different bacterial species.