Active release of bound antibody by Streptococcus mutans

Abstract

Previous studies have shown that Streptococcus mutans is capable of releasing many surface protein antigens, particularly antigen P1. Antigen P1 is immunodominant and has been implicated in adherence of S. mutans to the acquired pellicles. The purpose of this study is to investigate the significance of release of this antigen by the cells. S. mutans NG8 (serotype c) was incubated with an anti-P1 rabbit immunoglobulin G (IgG) or a human colostral IgA which contains natural anti-P1 activity. Results indicated that the bound antibodies were released by the cells in a pH-and time-dependent manner. The optimal pH for release was between 6 and 8, and the release rate reached a plateau in 1 h at 37؇C. The release of bound antibodies was considered an active process, since heat-killed cells remained capable of antibody binding but failed to release the antibodies. The release was also dependent on the age of the culture, with early-exponential-phase cells releasing the maximum amount of bound IgG. The released IgG was isolated by polyethylene glycol precipitation and protein A-Sepharose column chromatography and found to be associated with antigen P1, indicating that the antibodies were released together with the antigen in the form of immune complexes. The binding of S. mutans by secretory IgA (SIgA) inhibited the adherence of the cells to salivary agglutinin-coated hydroxylapatite. However, when the SIgA-coated S. mutans was allowed to release the bound antibodies, the inhibitory effect of SIgA on adherence was abrogated. These results suggest that S. mutans is capable of shedding surface-bound antibodies in the form of antibody-antigen immune complexes. Such an action may be a strategy employed by the cells to counter the neutralizing effect of naturally occurring antibodies in the oral cavity.

Fraction 1 capsular antigen (F1) purification from Yersinia pestis CO92 and from an Escherichia coli recombinant strain and efficacy against lethal plague challenge

“…One explanation of this observation may be that even though high levels of F1 antibody are present, cell-free F1 may bind significant quantities of this circulating immunoglobulin, titrating out its activity. Alternatively, cell-associated F1 which has bound antibody may be sloughed from the bacteria as has been described for some antibody-bound streptococcal surface antigens (24). These immune-avoidance hypotheses are consistent with our observation that the bulk of the F1 is released from the microorganism in vitro after an extended growth period.…”

Clonal diversity of Streptococcus mitis biovar 1 isolates from the oral cavity of human neonates

“…For example, oral bacteria such as Streptococcus sanguis, Streptococcus oralis, and a significant number of strains of S. mitis biovar 1 produce an IgA1 protease capable of cleaving IgA1 antibodies (13,40). Secreted antigens may bind antibody away from the bacterial cell surface (29), or host salivary macromolecules may mask bacterial cell-surface antigens from immune recognition. Chronic exposure of the host to resident bacteria may give rise to the induction of low-avidity antibody (14).…”

Role of C-Terminal Domains in Surface Attachment of the Fructosyltransferase of Streptococcus salivariusATCC 25975

“…Surface protein-releasing enzyme activity has been characterized in some pathogenic streptococci (16). Other studies have shown that oral streptococci release surface proteins, particularly antigens such as antigen A and protein P1, by the action of endogenous proteinases (7,17). The implication of these studies is that these streptococci shed antibody-antigen complexes as a means of evading the host immune system (15).…”