Apoptosis of mouse dendritic cells is triggered by listeriolysin, the major virulence determinant of Listeria monocytogenes

Abstract

Infection of a murine-spleen dendritic cell line by Listeria monocytogenes was found to induce cell death through apoptosis. To characterize the bacterial product(s) involved in induction of apoptosis, dendritic cells were infected with the L. monocytogenes EGD strain and several isogenic mutants deficient in the production of individual listerial virulence factors. The ability to induce cellular apoptosis was retained by all mutants tested, except the prfA and delta hly mutants, both of which are unable to produce listeriolysin. Apoptosis was also induced by purified listeriolysin suggesting that this protein directly induces apoptosis. Purified recombinant listeriolysins rendered either weakly haemolytic by a C-484 to S mutation, or nonhaemolytic by a W-491 to A mutation exhibited little or no capacity to induce apoptosis, indicating that both activities are associated within the same protein region. Treatment with purified listeriolysin or L. monocytogenes infection also triggers apoptosis in explanted bone-marrow dendritic cells. Thus invasion of dendritic cells by L. monocytogenes, which results in cell death, may play an important role in the pathogenesis of listerial infections by impairing immune responses, hindering bacterial clearance and promoting spread of the infection.

Recombinant E. coli efficiently delivers antigen and maturation signals to human dendritic cells: Presentation of MART1 to CD8+ T cells

“…Clonal analysis of MART1-specific CTLs has shown that MART1/T-cell receptor interactions are tightly restricted to HLA-A2, 37 and a recent study found that mature human MoDCs do not efficiently process and present the MART1 [27][28][29][30][31][32][33][34][35] epitope from whole MART1 due to the presence of the immunoproteasome, 38 suggesting that delivery of some whole proteins, including MART1, may not be an effective method of antigen delivery to DCs. Immature DCs express both the standard proteasome and immunoproteasomes.…”

“…The presentation of the MART1 [27][28][29][30][31][32][33][34][35] epitope to the HLA-A2 molecule on MoDCs was examined by measuring IFN-␥ production by the CD8 ϩ T cells within the MART1-specific CTL population in response to E. coli-infected DCs. Immature DCs (10 5 cells, either HLA-matched and HLA-mismatched) were incubated with E. coli (at a ratio of 10 bacteria per DC for 16 hr) or pulsed with control peptides (10 g/ml, 1 hr).…”

“…In order to determine whether this phenomenon was restricted to OVA and murine APC/T-cell interactions, we investigated whether E. coli/LLO could be used to deliver the MART1 antigen to the MHC class I processing pathways of human DCs. Full-length 357 bp MART1 cDNA, containing the MART1 [27][28][29][30][31][32][33][34][35] HLA-A2-restricted epitope, was cloned into the pCRT7/CT-TOPO inducible expression vector. Inducible expression of MART1 protein was achieved in both native E. coli and E. coli/LLO (Fig.…”

“…As a consequence of the interaction with bacteria, human DCs undergo marked phenotypic and functional maturation. Furthermore, we show that fixed E. coli/ LLO expressing the well-characterised human melanoma antigen, MART1, 20,21 efficiently deliver the HLA-A2-restricted MART1 [27][28][29][30][31][32][33][34][35] epitope for processing and presentation on human MoDCs, suggesting the potential of this system as a novel strategy for human tumour immunotherapy.…”

Cell death during sepsis: integration of disintegration in the inflammatory response to overwhelming infection

“…GAS also elaborate the potent heterocyclic peptide cytolysin streptolysin S (SLS) [45] which can deplete host phagocytes and help promote bacterial survival [46] through a proinflammatory, calpaindependent cell death pathway [47] L. monocytogenes lyses the phagosomal membrane and escapes into the cytosol to initiate an intracellular infection, a process dependent on the pore-formin toxin listeriolysin O (LLO). Subsequently, intracellular L. monocytogenes induces LLO-dependent apoptosis in different cell types, including hepatocytes [48], lymphocytes [49] and dendritic cells [50]. LLO might insert into the mitochondrial membrane, allowing release of cytochrome c or efflux of Ca 2?…”