Histoplasma capsulatumYeasts Are Phagocytosed Via Very Late Antigen-5, Killed, and Processed for Antigen Presentation by Human Dendritic Cells

Abstract

Histoplasma capsulatum (Hc) is a facultative, intracellular parasite of world-wide importance. As the induction of cell-mediated immunity to Hc is of critical importance in host defense, we sought to determine whether dendritic cells (DC) could function as a primary APC for this pathogenic fungus. DC obtained by culture of human monocytes in the presence of GM-CSF and IL-4 phagocytosed Hc yeasts in a time-dependent manner. Upon ingestion, the intracellular growth of yeasts within DC was completely inhibited compared with rapid growth within human macrophages. Electron microscopy of DC with ingested Hc revealed that many of the yeasts were degraded as early as 2 h postingestion. In contrast to macrophages, human DC recognized Hc yeasts via the fibronectin receptor, very late Ag-5, and not via CD18 receptors. DC stimulated Hc-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of viable and heat-killed Hc yeasts, but greater proliferation was achieved after ingestion of viable yeasts. These data demonstrate that human DC can phagocytose and degrade a fungal pathogen and subsequently process the appropriate Ags for stimulation of lymphocyte proliferation. In vivo, such interactions between DC and Hc may facilitate the induction of cell-mediated immunity.

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).…”

“…Human DCs have recently been shown to phagocytose a variety of microbial pathogens efficiently, including Listeria monocytogenes, 25,26 Borrelia burgdorferi, 27 Mycobacterium tuberculosis, 15 M. bovis BCG, 28 Histoplasma capsulatum, 29 and Streptococcus gordonii. 30 Although murine DCs have previously been shown to take up E. coli, we wished to determine the efficiency with which human MoDCs phagocytose recombinant E. coli.…”

“…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.…”