Human dendritic cells respond to Porphyromonas gingivalis LPS by promoting a Th2 effector response in vitro

Understanding how mucosal pathogens modulate the immune response may facilitate the development of vaccines for disparate human diseases. In the present study, human monocyte-derived DC (MDDC) were pulsed with LPS of the oral pathogen Porphyromonas gingivalis and Escherichia coli 25922 and analyzed for: (i) production of Th-biasing/inflammatory cytokines; (ii) maturation/costimulatory molecules; and (iii) induction of allogeneic CD4⁺ and naive CD45RA⁺ T cell proliferation and release of Th1 or Th2 cytokines. We show that E. coli LPS-pulsed MDDC released Th1-biasing cytokines - consisting of high levels of IL-12 p70, IFN-γ-inducible protein 10 (IP-10) - but also TNF-α, IL-10, IL-6 ana IL-1β. In contrast, no IL-12 p70 or IP-10, and lower levels of TNF-α and IL-10 were induced by P. gingivalis LPS. These differences were sustained at LPS doses that yielded nearly equivalent maturation of MDDC; moreover the T cell response was consistent: E. coli LPS-pulsed MDDC induced higher T cell proliferation, and T cells released more IFN-γ and IL-2, but less IL-5 than T cells co-cultured with P. gingivalis LPS pulsed-MDDC. IL-13 was secreted by naive CD45RA⁺CD45RO^-CD4⁺T cells in response to P. gingivalisLPS-pulsed MDDC. These results suggest that human MDDC can be polarized by LPS from the mucosal pathogen P. gingivalis to induce a Th2 effector response in vitro.