Interleukin-1ß is internalised by viable Aggregatibacter actinomycetemcomitans biofilm and locates to the outer edges of nucleoids.

ABSTRACT

The opportunistic pathogen Aggregatibacter actinomycetemcomitans causes periodontitis, which is a biofilm infection that destroys tooth-supportive tissues. Interleukin (IL)-1ß, a central proinflammatory cytokine of periodontitis, is an essential first line cytokine for local inflammation that modulates the cell proliferation and anti-pathogen response of human gingival keratinocytes. Previously, we demonstrated that A. actinomycetemcomitans biofilms bind IL-1ß; however, whether this binding is an active process is not known. In this study, we showed for the first time with immuno-electron microscopy that viable bacterial biofilm cells internalised IL-1ß when co-cultured with an organotypic mucosa. Decreased biofilm viability hindered the ability of biofilm to sequester IL-1ß and caused IL-1ß leakage into the culture medium. In some A. actinomycetemcomitans cells, intracellular IL-1ß localized to the outer edges of the nucleoids. We identified the DNA-binding protein HU as an IL-1ß interacting protein with mass spectroscopy and showed the interaction of recombinant HU and IL-1ßin vitro using enzyme-linked immunosorbent assay (ELISA). Close contact with a viable A. actinomycetemcomitans biofilm decreased the proliferation and apoptosis of human gingival keratinocytes as demonstrated using Ki-67 and the terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining, respectively. Our results suggest that viable A. actinomycetemcomitans biofilms may disturb the critical first steps of local inflammation in periodontitis by binding and internalising IL-1ß. The interaction of IL-1ß with conserved HU provides a potential mechanism for shaping bacterial gene expression.