Abstract Mucosal IgA secreted by local plasma cells (PCs) is a critical component of mucosal immunity. Although IgA class switching can occur at mucosal sites in a T cell-independent manner, 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 TGFb1 and IL-21, produced by follicular helper T cells (TFH), synergize to generate abundant IgA-plasmablasts (PBs) that express CCR10. In the presence of IL-21, TGFb1 promotes naive B cell proliferation and differentiation. In addition it overrides IL-21-induced IgG class switching in favor of IgA. Furthermore, in combination with IL-21, TGFb1 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+ cells in tonsil GCs. In conclusion, TFH, through IL-21 and TGFb1 contribute to the generation of human mucosal-homing IgA+ PCs. Thus, mucosal vaccines should aim to induce robust TFH responses.
Abstract Dectin-1 recognizing fungal pathogens and mycobacteria, delivers intracellular signals to activate DCs. Here we report that Dectin-1 expressed on human DCs possesses unique immunological function that potentiates antigen-specific CD8+ T cell responses. We first generated an agonistic anti-Dectin-1 monoclonal antibody (mAb), which recognized Leu192-Asn202 in Dectin-1 and efficiently bound to both in vitro monocyte-derived DCs and in vivo CD1c+ skin dermal DCs, but not Langerin cells. Syk-dependent activation by anti-Dectin-1 mAb induced DCs to upregulate T cell costimulatory molecules, particularly CD70 and 4-1BBL, as well as cytokines and chemokines. This signaling via Dectin-1 allowed DCs to potentiate both memory and naïve CD8+ T cell responses by promoting their expansions and functional activities. Furthermore, both neo- and non-self-antigens delivered to DCs via Dectin-1 resulted in potent antigen-specific CD8+ T cell responses. This was largely dependent on CD70 and 4-1BBL upregulated by the signaling via Dectin-1. We also demonstrated that Dectin-1-mediated activation of DCs did not promote Foxp3+ and IL-10-producing regulatory CD4+ T cell responses, but potentiated CD4+ helper T cell function for inducing effector CD8+ T cells. We conclude that Dectin-1 on human DCs has unique function for eliciting antigen-specific CD8+ T cell responses by taking up antigens and delivering intracellular signals favoring effector CD8+ T cell responses.
Dectin-1, a C-type lectin recognizing fungal and mycobacterial pathogens, can deliver intracellular signals that activate dendritic cells (DCs), resulting in initiation of immune responses and expansion of Th17 CD4(+) T cell responses. In this paper, we studied the roles of human Dectin-1 (hDectin-1) expressed on DCs in the induction and activation of Ag-specific CD8(+) T cell responses. We first generated an agonistic anti-hDectin-1 mAb, which recognizes the hDectin-1 Glu(143)-Ile(162) region. It bound to in vitro monocyte-derived DCs and to in vivo CD1c(+)CD1a(+) dermal DCs but not to epidermal Langerhans cells. Anti-hDectin-1-mediated DC activation resulted in upregulation of costimulatory molecules and secretion of multiple cytokines and chemokines in a Syk-dependent manner. DCs activated with the anti-hDectin-1 mAb could significantly enhance both neo and foreign Ag-specific CD8(+) T cell responses by promoting both the expansion of CD8(+) T cells and their functional activities. We further demonstrated that delivering Ags to DCs via hDectin-1 using anti-hDectin-1-Ag conjugates resulted in potent Ag-specific CD8(+) T cell responses. Thus, hDectin-1 expressed on DCs can contribute to the induction and activation of cellular immunity against intracellular pathogens, such as mycobacteria, that are recognized by DCs via Dectin-1. Vaccines based on delivering Ags to DCs with an agonistic anti-hDectin-1 mAb could elicit CD8(+) T cell-mediated immunity.
Abstract The mechanisms by which microbial vaccines interact with human APCs remain elusive. Herein, we describe the transcriptional programs induced in human DCs by pathogens, innate receptor ligands and vaccines. Exposure of DCs to influenza, Salmonella enterica and Staphylococcus aureus allows us to build a modular framework containing 204 transcript clusters. We use this framework to characterize the responses of human monocytes, monocyte-derived DCs and blood DC subsets to 13 vaccines. Different vaccines induce distinct transcriptional programs based on pathogen type, adjuvant formulation and APC targeted. Fluzone, Pneumovax and Gardasil, respectively, activate monocyte-derived DCs, monocytes and CD1c+ blood DCs, highlighting APC specialization in response to vaccines. Finally, the blood signatures from individuals vaccinated with Fluzone or infected with influenza reveal a signature of adaptive immunity activation following vaccination and symptomatic infections, but not asymptomatic infections. These data, offered with a web interface, may guide the development of improved vaccines.
Targeting of Ags directly to dendritic cells (DCs) through anti-DC receptor Ab fused to Ag proteins is a promising approach to vaccine development. However, not all Ags can be expressed as a rAb directly fused to a protein Ag. In this study, we show that noncovalent assembly of Ab-Ag complexes, mediated by interaction between dockerin and cohesin domains from cellulose-degrading bacteria, can greatly expand the range of Ags for this DC-targeting vaccine technology. rAbs with a dockerin domain fused to the rAb H chain C terminus are efficiently secreted by mammalian cells, and many Ags not secreted as rAb fusion proteins are readily expressed as cohesin directly fused to Ag either via secretion from mammalian cells or as soluble cytoplasmic Escherichia coli products. These form very stable and homogeneous complexes with rAb fused to dockerin. In vitro, these complexes can efficiently bind to human DC receptors followed by presentation to Ag-specific CD4⁺ and CD8⁺ T cells. Low doses of the HA1 subunit of influenza hemagglutinin conjugated through this means to anti-Langerin rAbs elicited Flu HA1-specific Ab and T cell responses in mice. Thus, the noncovalent assembly of rAb and Ag through dockerin and cohesin interaction provides a useful modular strategy for development and testing of prototype vaccines for elicitation of Ag-specific T and B cell responses, particularly when direct rAb fusions to Ag cannot be expressed.
The development of autoantibodies is a hallmark of systemic lupus erythematosus (SLE). SLE serum can induce monocyte differentiation into dendritic cells (DCs) in a type I IFN–dependent manner. Such SLE-DCs activate T cells, but whether they promote B cell responses is not known. In this study, we demonstrate that SLE-DCs can efficiently stimulate naive and memory B cells to differentiate into IgG- and IgA-plasmablasts (PBs) resembling those found in the blood of SLE patients. SLE-DC–mediated IgG-PB differentiation is dependent on B cell–activating factor (BAFF) and IL-10, whereas IgA-PB differentiation is dependent on a proliferation-inducing ligand (APRIL). Importantly, SLE-DCs express CD138 and trans-present CD138-bound APRIL to B cells, leading to the induction of IgA switching and PB differentiation in an IFN-α–independent manner. We further found that this mechanism of providing B cell help is relevant in vivo, as CD138-bound APRIL is expressed on blood monocytes from active SLE patients. Collectively, our study suggests that a direct myeloid DC–B cell interplay might contribute to the pathogenesis of SLE.
