Direct proteasome-independent cross-presentation of viral antigen by plasmacytoid dendritic cells on major histocompatibility complex class I

Abstract

Although plasmacytoid dendritic cells (pDCs) respond to virus replication in a non-specific fashion by producing large amounts of type I interferon, a rapid, direct role of pDCs in activating antiviral lymphocytes is less clear. Here we showed that pDCs possess the capacity to rapidly initiate antigenspecific antiviral CD8 + T cell responses. Following virus exposure, pDCs efficiently and rapidly internalized exogenous viral antigens and then presented those antigens on major histocompatibility complex (MHC) class I to CD8 + T cells. Processing of exogenous antigen occurred within endocytic organelles and did not require transit of antigen to the cytosol. Intracellular stores of MHC class I partially colocalized with transferrin receptor and internalized transferrin in endosomes, suggesting that such recycling endosomes are sites of peptide loading onto MHC class I or peptide transit. These data demonstrate that pDCs utilize ready-made stores of MHC class I to rapidly present exogenous antigen to CD8 + T cells.The high rate of viral replication represents a considerable challenge for the immune response. Human DCs can be classified into two major cell subsets, myeloid and plasmacytoid DCs, both of which are critical for the initiation of viral immune responses 1,2 . The presentation of viral peptides to CD4 + and CD8 + T cells is mediated by major histocompatibility complex (MHC) class II molecules and class I, respectively. DC maturation leads to a variety of changes including, activation induced antigen processing and increased surface expression of MHC class I and class II 3,4 . Exogenous antigen presentation on MHC class II molecules by myeloid DC (mDCs) is a rapid and coordinated process 5 . Pools of pre-synthesized MHC class II are stored in late endosomal and lysosomal compartments, which are loaded in an activationdependent manner and translocated to the cell surface 6-10 . NIH Public Access RESULTS pDCs drive CD8 + T cell proliferationHealthy donor pDCs and mDCs were purified from blood by negative depletion followed by direct cell sorting for mDCs (HLA-DR high CD11c high) and pDCs (HLA-DR high CD123 high). Their APC function was assessed by their ability to induce the proliferation of allogeneic (allo) CD4 + and CD8 + T cells. pDCs demonstrated no allo-stimulatory capacity for either CD4 + or CD8 + T cells, while mDCs showed low stimulatory capacity (data not shown). Upon activation with influenza virus, both pDCs and mDCs induced strong proliferation of allo-CD4 + and CD8 + T cells. Influenza virus-treated pDCs induced stronger allo-proliferation of CD8 + T cells when compared to their myeloid counterpart (Fig. 1a,b, upper panels). Reactivation of the pDC-expanded CD8 + T cells with anti-CD3 and anti-CD28 led to high levels of IFN-γ secretion, indicating the acquisition of effector function (data not shown). In contrast, influenza virus-treated mDCs induced a higher proliferation of allo-CD4 + T cells (Fig. 1a,b, bottom panels) indicating that the difference in CD8 + T cell proliferation wa...

Targeting Uptake Receptors on Human Plasmacytoid Dendritic Cells Triggers Antigen Cross-Presentation and Robust Type I IFN Secretion

“…However, for a potent antitumor response, both CD4 + and CD8 + T cell activation is essential. Although human pDCs were previously thought to poorly cross-present exogenous Ag to CD8 + T cells, accumulating evidence now suggests that human pDCs are endowed with an efficient cross-presenting machinery (9)(10)(11)(12)(13)(14). Just recently, we could demonstrate the potency of pDCs in a small cohort of metastatic melanoma patients, in whom vaccination with activated pDCs induced favorable immune responses and significantly extended overall survival (15).…”

Type I Interferons Mediate the Innate Cytokine Response to Recombinant Fowlpox Virus but Not the Induction of Plasmacytoid Dendritic Cell-Dependent Adaptive Immunity

“…This is profound, considering the important role type I IFNs play in regulating adaptive immunity to a number of other viral infections and, of particular note here, the dsDNA viruses VV and adenovirus (AdV5), which lack the ability to elicit an adaptive immune response in the absence of type I IFNs (61,62). We therefore propose that the main role of pDCs here is not to provide type I IFNs but to act as antigen-presenting cells (APCs) (13), a property recently shown to involve ligation of TLR7 and TLR9 (35), which are, coincidently, the two same TLRs that we have found to be responsible for innate recognition of FPV (E. L. Lousberg, submitted for publication). In antigen presentation experiments which involved the proliferation of OT-I T cells in vitro and in vivo, we demonstrated that pDCs had an important role in antigen presentation and were in fact responsible for presenting antigen to a significantly greater extent than cDCs when DCs were harvested from a previously immunized mouse and coincubated with OT-I T cells.…”

Fcγ receptor antigen targeting potentiates cross-presentation by human blood and lymphoid tissue BDCA-3+ dendritic cells

“…In contrast, in human plasmacytoid DCs, cross-presentation of viral antigen is independent of proteasome digestion, with all processing being performed in the endosomal pathway. 31 In ovalbumin cross-presentation by mouse DC systems, data collectively suggests that processing may occur in either the endosomal or cytosolic/proteasomal pathway, depending on the endocytic route taken (ie, choice of binding to endocytic receptors) and configuration of the antigen (ie, soluble or particulate). 4,15,28,32,33 Our data in human MoDCs now shows that for HCMV pp65, Fc␥R-mediated uptake potentiates crosspresentation in a manner that requires processing both in the endosomal pathway and by the proteasome.…”

“…3 Evidence for cytosolic entry of (partly) processed protein, and subsequent proteasome involvement is abundant, 33,36-38 but proteasome-independent routes have been described as well. 31,32 In case of proteasome-dependent cross-presentation, newly formed peptides could enter the ER 39 For personal use only. on May 12, 2018.…”