Dental plaque biofilm transforms host-derived β2-microglobulin into polymorphic fibrils for integration into the biofilm matrix

Dental plaque is a polymicrobial biofilm formed on tooth surfaces despite continuous exposure to variable host-derived antimicrobial factors. To date, the underlying mechanisms remain nebulous. This study aimed to determine whether dental plaque biofilms affect the major salivary antimicrobial protein β₂-microglobulin (B2M). Immunostaining of human dental plaque specimens with an anti-B2M antibody revealed that B2M exists as elongated fibers, punctate structures, and amorphous aggregates. Fractionation of dental plaque suspensions revealed that B2M was present in both the soluble and insoluble fractions. B2M, which forms insoluble fibrils associated with dialysis-related amyloidosis, exhibited comparable fibril-forming properties in dental plaque. Immunostaining with a developed anti-B2M amyloid fibril antibody showed that fibrillar B2Ms (fB2Ms) were distributed throughout the dental plaque specimens. <i>In vitro</i> experiments using purified B2M demonstrated that environmental factors characteristic of dental plaque, specifically phosphate ions, bacterial short-chain fatty acids (acetic, butyric, lactic, and propionic acids), and divalent calcium and magnesium ions, significantly promoted fB2M formation. In a <i>Streptococcus mutans</i> biofilm model, native B2M transformed into fibrils only in the presence of these environmental factors, resulting in the loss of its antimicrobial activity and its incorporation into the biofilm matrix. The preformed fB2Ms increased <i>S. mutans</i> biofilm growth, decreased biofilm adhesion, and transformed the biofilm matrix architecture from a membranous to a reticulated organization, potentially facilitating biofilm dissemination. Dental plaque biofilms employed a specialized "molecular hijacking" strategy to counteract host defense mechanisms and ensure persistence through fibrillation. Our findings provide novel insights into biofilm pathogenesis, host-microbe interactions, and potential plaque control approaches.