Functional Role of Secretory IgA1 and IgA2 Antibodies Against Streptococcus Mutans

Abstract

Previously, we have reported that dental caries-resistant (CR) subjects have significantly higher levels of parotid salivary immunoglobulin A (IgA) and serum IgG antibodies to Streptococcus mutans antigens than caries-susceptible (CS) individuals by enzyme-linked immunosorbent assay (ELISA). Furthermore, we have shown that unfractionated parotid saliva and sera from CR volunteers inhibit S. mutans enzyme activities more than CS samples. CS individuals had higher levels of total parotid salivary IgA1 and IgA2 than CR subjects. There were higher levels of parotid salivary IgA2, but not IgA1, antibodies to S. mutans by ELISA in CR subjects than CS individuals. We have now purified IgA1 and IgA2 from pooled parotid saliva of CR and CS subjects using jacalin-agarose. Pooled CS IgA1 and IgA2 inhibited S. mutans growth more than CR samples on an equal weight basis at 10 ng/ml. CS IgA1 inhibited S. mutans adherence more than CR IgA1. IgA1 and IgA2 from both CR and CS individuals inhibited S. mutans acid production equally. In contrast, CR IgA1 and IgA2 inhibited S. mutans glucosyltransferase (GTF) and glucose-phosphotransferase (PTS) enzyme activity more than CS fractions. Purified colostral IgA2 at 550 ng/ml inhibited S. mutans growth and GTF enzyme activity better than IgA1 from the same woman at the same concentration. These results suggest that IgA1 and IgA2 antibodies from caries immune subjects inhibit S. mutans enzyme activity better than growth, adherence and acid production and indicate that the IgA1 and IgA2 purification may remove an important anti-S. mutans factor. Furthermore, the data suggest that IgA2 may be better at inhibiting S. mutans virulence factors than IgA1