Cytokine release and NLRP3 inflammasome activation induced by low-abundance oral bacterial biofilms.

Background: Low-abundance bacterial (LAB) species, despite their low prevalence, may contribute to oral inflammatory diseases by triggering host immune responses. The NLRP3 inflammasome plays a key role in inflammation, but its activation by LAB species remains unclear. Aim: This study examined whether selected LAB species and their biofilm-secreted components induce cytokine production and inflammasome activation in human peripheral blood mononuclear cells (PBMCs). Methods: Biofilms of selected LAB species were established, and supernatants were collected. PBMCs were stimulated with biofilms or supernatants, and cytokine levels were quantified using ELISA. The expression of NLRP3 and Caspase-1 genes was analyzed through real-time PCR. Results: Biofilms induced significantly higher levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, and IL-18) compared to supernatants, with C. hominis, N. flavescens, and D. pneumosintes being the most potent inducers. Biofilms also led to a marked increase in NLRP3 expression, while supernatants primarily activated Caspase-1 expression, indicating distinct inflammasome activation pathways. Conclusions: These findings highlight the immunostimulatory potential of LAB species, particularly their ability to activate NLRP3 and drive inflammation. The differential activation of NLRP3/Caspase-1 by biofilms and supernatants suggests distinct pathogenic mechanisms. Targeting such mechanisms/pathways could offer new therapeutic strategies to mitigate inflammation linked to oral infections.