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.