Macrophage Subset Sensitivity to Endotoxin Tolerisation by Porphyromonas gingivalis

Macrophages (M Phi s) determine oral mucosal responses; mediating tolerance to commensal microbes and food whilst maintaining the capacity to activate immune defences to pathogens. MW responses are determined by both differentiation and activation stimuli, giving rise to two distinct subsets; pro-inflammatory M1- and anti-inflammatory/regulatory M2-M Phi s. M2-like subsets predominate tolerance induction whereas M1 M Phi s predominate in inflammatory pathologies, mediating destructive inflammatory mechanisms, such as those in chronic P. gingivalis (PG) periodontal infection. MW responses can be suppressed to benefit either the host or the pathogen. Chronic stimulation by bacterial pathogen associated molecular patterns (PAMPs), such as LPS, is well established to induce tolerance. The aim of this study was to investigate the susceptibility of MW subsets to suppression by P. gingivalis. CD14(hi) and CD14(lo) M1- and M2-like MWs were generated in vitro from the THP-1 monocyte cell line by differentiation with PMA and vitamin D-3, respectively. MW subsets were pre-treated with heat-killed PG (HKPG) and PG-LPS prior to stimulation by bacterial PAMPs. Modulation of inflammation was measured by TNF alpha, IL-1 beta, IL-6, IL-10 ELISA and NF beta B activation by reporter gene assay. HKPG and PG-LPS differentially suppress PAMP-induced TNFa, IL-6 and IL-10 but fail to suppress IL-1b expression in M1 and M2 M Phi s. In addition, P. gingivalis suppressed NF beta B activation in CD14(lo) and CD14(hi) M2 regulatory MWs and CD14(lo) M1 M Phi s whereas CD14(hi) M1 pro-inflammatory M Phi s were refractory to suppression. In conclusion, P. gingivalis selectively tolerises regulatory M2 M Phi s with little effect on proinflammatory CD14(hi) M1 M Phi s; differential suppression facilitating immunopathology at the expense of immunity.