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...

Summary Mucosal IgA secreted by local plasma cells (PCs) is a critical component of mucosal immunity. Although IgA class switching can occur at mucosal sites, high-affinity PCs are optimally generated in germinal centers (GCs) in a T cell-dependent fashion. However, the mechanism of how CD4+ helper T cells induce mucosal-homing IgA-PCs remains unclear. We show here that TGFβ1 and IL-21, produced by follicular helper T cells (TFH), synergize to generate abundant IgA-plasmablasts (PBs). In the presence of IL-21, TGFβ1 promotes naive B cell proliferation and differentiation, and it overrides IL-21-induced IgG class switching in favor of IgA. Furthermore, in combination with IL-21, TGFβ1 downregulates CXCR5 while upregulating CCR10 on PBs, enabling their exit from GCs and migration towards local mucosa. This is supported by the presence of CCR10+IgA+PBs in tonsil GCs. These findings show that TFH contribute to mucosal IgA. Thus, mucosal vaccines should aim to induce robust TFH responses.

Objective Targeting HIV antigens directly to dendritic cells using monoclonal antibodies against cell-surface receptors has been shown to evoke potent cellular immunity in animal models. The objective of this study was to configure an anti-human CD40 antibody fused to a string of five highly conserved CD4+ and CD8+ T-cell epitope-rich regions of HIV-1 Gag, Nef and Pol (αCD40.HIV5pep), and then to demonstrate the capacity of this candidate therapeutic vaccine to target these HIV peptide antigens to human dendritic cells to expand functional HIV-specific T cells. Methods Antigen-specific cytokine production using intracellular flow cytometry and multiplex bead-based assay, and suppression of viral inhibition, were used to characterize the T cells expanded by αCD40.HIV5pep from HIV-infected patient peripheral blood mononuclear cell (PBMC) and dendritic cell/T-cell co-cultures. Results This candidate vaccine expands memory CD4+ and CD8+ T cells specific to multiple epitopes within all five peptide regions across a wide range of major histocompatibility complex (MHC) haplotypes from HIV-infected patient PBMC and dendritic cell/T-cell co-cultures. These in vitro expanded HIV antigen-specific CD4+ and CD8+ T cells produce multiple cytokines and chemokines. αCD40.HIV5pep-expanded CD8+ T cells have characteristics of cytotoxic effector cells and are able to kill autologous target cells and suppress HIV-1 replication in vitro. Conclusion Our data demonstrate the therapeutic potential of this CD40-targeting HIV candidate vaccine in inducing a broad repertoire of multifunctional T cells in patients.

Monocytes exposed to serum from SLE patients promote B cell differentiation to IgG and IgA plasmablasts dependent on BAFF and IL-10 or APRIL, respectively.

Dendritic cells (DCs) are major antigen-presenting cells that can efficiently prime and cross-prime antigen-specific T cells. Delivering antigen to DCs via surface receptors is thus an appealing strategy to evoke cellular immunity. Nonetheless, which DC surface receptor to target to yield the optimal CD8+ and CD4+ T cell responses remains elusive. Herein, we report the superiority of CD40 over 9 different lectins and scavenger receptors at evoking antigen-specific CD8+ T cell responses. However, lectins (e.g., LOX-1 and Dectin-1) were more efficient than CD40 at eliciting CD4+ T cell responses. Common and distinct patterns of subcellular and intracellular localization of receptor-bound αCD40, αLOX-1 and αDectin-1 further support their functional specialization at enhancing antigen presentation to either CD8+ or CD4+ T cells. Lastly, we demonstrate that antigen targeting to CD40 can evoke potent antigen-specific CD8+ T cell responses in human CD40 transgenic mice. This study provides fundamental information for the rational design of vaccines against cancers and viral infections.