Porphyromonas gingiva/is Escape from Autophagy in Human Myeloid Dendritic Cells via Minor Mfa-1 Fimbria- DC-SIGN Interactions

Abstract

In professional phagocytes, early receptor recognition is crucial to determine the fate of engulfed microorganisms. Among the many pattern recognition receptors (PRRs) expressed by dendritic cells (DCs), the C-type lectin DC-SIGN is of particular interest as it has been associated with immunosuppression by infecting pathogens. While autophagy has emerged as a major immune mechanism against microbes, very little is presently understood about its role in elimination of intracellular pathogens; especially in the context of the PRR diversity expressed by DCs. Hence, the study aimed to investigate the role of DC-SIGN targeting by the anaerobic pathogen Porphyromonas gingiva/is in its intracellular survival within myeloid DCs and how intracellular routing through early and late endosomes. autophagosomes and lysosomes relate to this survival. Employed in this investigation were human monocyte derived DCs and a panel of isogenic fimbriae deficient mutant strains of P. gingivabs that express the DC-SIGN ligand (Mfa-1 fimbriae) and/or the TLR2 ligand (FimA fimbriae). The results show that uptake of P. gingiva/is by the nonDC- SJGN dependent route resulted in intracellular killing and elimination of intracellular content of P. gingiva/is. This route was associated with early endosomal routing through Rab5, increased LC3-ll and LAMP-l, as well as the formation of double membrane intracellular phagophores. In contrast, DC -SIGN dependent uptake did not induce significant levels of Rab5, LC3- IL and LAMP 1. Moreover, P. gingiva/is was mostly contained within single membrane vesicles where it survived intracellularly. Survival was ameliorated by forced autophagy. These results suggest that myeloid DCs are fully capable of eliminating intracellular pathogens by autophagy but that selective engagement of DC-SIGN is a microbial tactic for evasion of antibacterial autophagy leading to intracellular survival.