Oral Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Porphyromonas gingivalis surface-associated molecules stimulate a host immune response (#9)

Jacqueline E. Heath 1 , Jason C. Lenzo 1 , James A. Holden 1 , Christine A. Seers 1 , Catherine A. Butler 1 , Paul D. Veith 1 , Neil M. O'Brien-Simpson 1 , Eric C. Reynolds 1
  1. Oral Health CRC, Melbourne Dental School and Bio21 Institute, The University of Melbourne, Carlton, VIC, Australia
The Gram-negative oral pathogen Porphyromonas gingivalis produces surface-associated virulence factor proteins that are exported across the OM using the Type IX Secretion System (T9SS). The abundant P. gingivalis virulence factors and T9SS substrates, the gingipains, are involved in host cell interactions and the aberrant pro-inflammatory host immune response. An lptO- mutant, deficient in the LptO component of the T9SS and a pg1058- mutant deficient in the PG1058 component, were shown to lack the surface-associated T9SS substrates. The influence of the T9SS on interactions of P. gingivalis with the human host and the ability of P. gingivalis to stimulate a pro-inflammatory host immune response were assessed in-vitro, by comparing responses to wild-type to the pg1058- and lptO- T9SS mutants. Susceptibility to macrophage phagocytosis was assessed using bacterial labelling and flow cytometry which was in the order wild-type>pg1058->lptO-. Host cell receptor signalling pathways were assessed using cell line reporter assays. NF-kB activation was induced equally by the wild-type, pg1058- and lptO- mutants, whereas the ability to stimulate TLR2 signalling was in the order pg1058->lptO->wild-typewhilst the ability to stimulate TLR4 signalling was in the order lptO->pg1058->wild-type. Stimulation of cytokine production by macrophages, epithelia and endothelia upon exposure to P. gingivalis was assessed using a Bioplex assay. The wild-type and T9SS mutants stimulated equivalent pro-inflammatory cytokine production by the macrophages. The epithelial and endothelial cells constitutively produced low levels of several cytokines. Cytokine production by epithelia and endothelia was either suppressed or cytokines were degraded by the wild-type, whilst the pg1058- mutant showed a reduction in epithelial cytokine production. Together these data suggest that in addition to the T9SS substrates there are differences in the surface-associated molecules of the wild-type, pg1058- and lptO- T9SS mutants which can influence human host interactions and immune response and thereby the virulence of P. gingivalis.