Regulation of phagosomal maturation in dendritic cells upon TLR stimulation

ALLOATTI, ANDRÉS; HOFFMANN, EIK; VARGAS, PABLO; SAN ROMAN, MABEL; KOTSIAS, FIORELLA; LENNON, ANA-MARIA; AMIGORENA, SEBASTIAN

Amsterdam

Congreso; V EMBO meeting 2013; 2013

EMBO

Clearance of pathogens plays a critical role in innate and adaptive immunity. Phagosomal fusion with late endosomes and lysosomes enhances proteolysis, causing degradation of the phagocytic content, especially in macrophages and neutrophils. In dendritic cells (DCs), however, phagocytosis serves a different function: it provides immunogenic peptides for antigen presentation to initiate immune responses. Therefore, the phagocytic pathway in DCs is organized to prevent antigen destruction. In DCs, stimulation of particular Toll-like receptors (TLRs) can influence the rate of phagosome fusion with lysosomes, thereby modulating both antigen degradation and presentation. We show here, that in bone marrow-derived DCs, stimulation of TLR4 by lipopolysaccharide (LPS) delays fusion between phagosomes and lysosomes by a yet unknown mechanism. Using ovalbumin-conjugated beads as a model system, we applied video microscopy as well as ultra-structural approaches and showed that pre-treatment of cells with LPS leads to clustering of lysosomes in the peri-nuclear region in a subpopulation of DCs. These cells displayed strongly reduced phago-lysosomal fusion activity measured by flow cytometry-based single organelle analysis. In addition, stimulation of TLR4 also increased cross-presentation of both bead-bound and soluble antigens to antigen-specific T lymphocytes. Altogether, our results provide evidence that TLR stimulation allows DCs to re-organize the distribution of late endosomes and lysosomes, in order to regulate phagosomal maturation for efficient antigen presentation by impairing the activity of phago-lysosomal fusion.