Analysis of Streptococcus mutans biofilm proteins recognized by salivary immunoglobulin A

The purpose of this study was to examine the Streptococcus mutans biofilm cellular proteins recognized by immunoglobulin A (IgA) in saliva from various caries-defined populations.

Biofilm and planktonic S. mutans UA159 cells were prepared. The proteins were extracted, separated by two-dimensional gel electrophoresis, transferred to blotting membranes, and probed for IgA using individual saliva samples from three groups of subjects; those who developed 0 caries (no active caries), 5-9 caries (medium), or more than 10 caries (severe) over a 12-month interval.

Several proteins were recognized by salivary IgA in all groups of saliva but spot distribution and intensity varied greatly between the groups, and some proteins were recognized more strongly in biofilm cells than in planktonic culture, and vice versa. Furthermore, 15 proteins were only recognized by saliva from the 'no active caries' group, and four proteins were recognized by saliva samples from subjects in all three groups. Specifically, antigen I/II was recognized less in biofilm cells by caries-free saliva compared with planktonic cells. However, salivary IgA antibody to antigen I/II was absent in blots using saliva from the 'medium caries' and 'severe caries' groups.

The bacterial molecules recognized by caries-free saliva are significant factors for S. mutans caries formation, and their inhibition could be a therapeutic target. In addition, saliva of caries-free subjects includes significant IgA antibody against antigen I/II of S. mutans, indicating a protective mechanism. However, microorganisms may protect themselves from host immune attack by forming biofilms and decreasing expression of antigen I/II.