Wataru Ise

Peripheral CD103+ dendritic cells form a unified subset developmentally related to CD8α+ conventional dendritic cells

Although CD103-expressing dendritic cells (DCs) are widely present in nonlymphoid tissues, the transcription factors controlling their development and their relationship to other DC subsets remain unclear. Mice lacking the transcription factor Batf3 have a defect in the development of CD8α+ conventional DCs (cDCs) within lymphoid tissues. We demonstrate that Batf3−/− mice also lack CD103+CD11b− DCs in the lung, intestine, mesenteric lymph nodes (MLNs), dermis, and skin-draining lymph nodes. Notably, Batf3−/− mice displayed reduced priming of CD8 T cells after pulmonary Sendai virus infection, with increased pulmonary inflammation. In the MLNs and intestine, Batf3 deficiency resulted in the specific lack of CD103+CD11b− DCs, with the population of CD103+CD11b+ DCs remaining intact. Batf3−/− mice showed no evidence of spontaneous gastrointestinal inflammation and had a normal contact hypersensitivity (CHS) response, despite previous suggestions that CD103+ DCs were required for immune homeostasis in the gut and CHS. The relationship between CD8α+ cDCs and nonlymphoid CD103+ DCs implied by their shared dependence on Batf3 was further supported by similar patterns of gene expression and their shared developmental dependence on the transcription factor Irf8. These data provide evidence for a developmental relationship between lymphoid organ–resident CD8α+ cDCs and nonlymphoid CD103+ DCs.

Memory B cells

The immune system can remember a previously experienced pathogen and can evoke an enhanced response to reinfection that depends on memory lymphocyte populations. Recent advances in tracking antigen-experienced memory B cells have revealed the existence of distinct classes of cells that have considerable functional differences. Some of these differences seem to be determined by the stimulation history during memory cell formation. To induce rapid recall antibody responses, the contributions of other types of cells, such as memory T follicular helper cells, have also now begun to be appreciated. In this Review, we discuss these and other recent advances in our understanding of memory B cells, focusing on the underlying mechanisms that are required for rapid and effective recall antibody responses.

Regulatory T Cells Control Antigen-Specific Expansion of Tfh Cell Number and Humoral Immune Responses via the Coreceptor CTLA-4

CD4(+)Foxp3-expressing Treg cells, which constitutively express the inhibitory coreceptor CTLA-4, are indispensable for immune homeostasis. We determined the roles of Treg cells and T follicular regulatory (Tfr) cells in the control of humoral immune responses. Depletion of Treg cells, blocking of CTLA-4 or a Treg cell specific reduction in CTLA-4 expression, resulted in an increase in the formation of antigen-specific Tfh cells, germinal center (GC), and plasma and memory B cells after vaccination. In the absence of Treg cell-expressed CTLA-4, large numbers of Tfr cells were present but were unable to restrain Tfh cell and GC formation. Temporary Treg cell depletion during primary immunization was sufficient to enhance secondary immune responses. Treg cells directly inhibited, via CTLA-4, B cell expression of CD80 and CD86, which was essential for Tfh cell formation. Thus, Treg and Tfr cells control Tfh cell and germinal center development, via CTLA-4-dependent regulation of CD80 and CD86 expression.

Naive CD4+ T Cells Exhibit Distinct Expression Patterns of Cytokines and Cell Surface Molecules on Their Primary Responses to Varying Doses of Antigen

The amount of an Ag used for stimulation affects the type and magnitude of T cell responses. In this study we have investigated the primary response of naive CD4+ T cells derived from OVA-specific TCR-transgenic mice (OVA23-3) upon stimulation with varying doses of the antigenic peptide, OVA323–339. IL-4 expression was maximal with 50 nM Ag and decreased significantly with increasing doses. In contrast, IFN-γ expression, which was also detected at 50 nM Ag, increased with increasing doses. The expression patterns of mRNA for the Th2-specific transcription factors GATA-3 and c-Maf were parallel to that of IL-4. These expression profiles were not altered by the addition of anti-IL-4 plus anti-IL-12 mAbs, suggesting that cytokine receptor signaling is not essential. Naive CD4+ T cells stimulated with 5 nM Ag elicited IgM secretion from cocultured B cells, whereas those stimulated with 50 nM Ag or more elicited apoptosis of B cells. This may be because at lower doses of Ag (5 nM), naive CD4+ T cells express CD40 ligand and OX40, whereas at higher doses (50 nM), they express Fas ligand. Clearly, the expression of each type of molecule depends on the Ag dose, and different molecules had different expression patterns. Thus, in the primary response, naive CD4+ T cells can exhibit different functions depending on the dose of Ag.

Memory B cells contribute to rapid Bcl6 expression by memory follicular helper T cells.

Significance Follicular helper T (TFH) cells have emerged as the key cell type required for the formation of germinal centers and subsequent long-lasting antibody responses. It has been demonstrated that TFH cells enter the memory pool. However, it is unclear how the generation, survival, or activation of those TFH memory cells is regulated. Here we show that B-cell lymphoma 6 (Bcl6), a master regulator of TFH generation, is required for maintenance of TFH memory cells and subsequent humoral memory. In these recall responses, antigen-specific memory B cells majorly contribute to the quick induction of Bcl6 in TFH memory cells. Our results reinforce the importance of cognate interaction between memory TFH and memory B cells and give important implications for development of better vaccines. In primary humoral responses, B-cell lymphoma 6 (Bcl6) is a master regulator of follicular helper T (TFH) cell differentiation; however, its activation mechanisms and role in memory responses remain unclear. Here we demonstrate that survival of CXCR5+ TFH memory cells, and thus subsequent recall antibody response, require Bcl6 expression. Furthermore, we show that, upon rechallenge with soluble antigen Bcl6 in memory TFH cells is rapidly induced in a dendritic cell-independent manner and that peptide:class II complexes (pMHC) on cognate memory B cells significantly contribute to this induction. Given the previous evidence that antigen-specific B cells residing in the follicles acquire antigens within minutes of injection, our results suggest that memory B cells present antigens to the cognate TFH memory cells, thereby contributing to rapid Bcl6 reexpression and differentiation of the TFH memory cells during humoral memory responses.

Orally Tolerized T Cells Can Form Conjugates with APCs but Are Defective in Immunological Synapse Formation

Oral tolerance is systemic immune hyporesponsiveness induced by the oral administration of soluble Ags. Hyporesponsiveness of Ag-specific CD4 T cells is responsible for this phenomenon. However, the molecular mechanisms underlying the hyporesponsive state of these T cells are not fully understood. In the present study, we investigated the ability of orally tolerized T cells to form conjugates with Ag-bearing APCs and to translocate TCR, protein kinase C-θ (PKC-θ), and lipid rafts into the interface between T cells and APCs. Orally tolerized T cells were prepared from the spleens of OVA-fed DO11.10 mice. Interestingly, the orally tolerized T cells did not show any impairment in the formation of conjugates with APCs. The conjugates were formed in a LFA-1-dependent manner. Upon antigenic stimulation, the tolerized T cells could indeed activate Rap1, which is critical for LFA-1 activation and thus cell adhesion. However, orally tolerized T cells showed defects in the translocation of TCR, PKC-θ, and lipid rafts into the interface between T cells and APCs. Translocation of TCR and PKC-θ to lipid raft fractions upon antigenic stimulation was also impaired in the tolerized T cells. Ag-induced activation of Vav, Rac1, and cdc42, which are essential for immunological synapse and raft aggregation, were down-regulated in orally tolerized T cells. These results demonstrate that orally tolerized T cells can respond to specific Ags in terms of conjugate formation but not with appropriate immunological synapse formation. This may account for the hyporesponsive state of orally tolerized T cells.

Sialylation converts arthritogenic IgG into inhibitors of collagen-induced arthritis

Rheumatoid arthritis (RA)-associated IgG antibodies such as anti-citrullinated protein antibodies (ACPAs) have diverse glycosylation variants; however, key sugar chains modulating the arthritogenic activity of IgG remain to be clarified. Here, we show that reduced sialylation is a common feature of RA-associated IgG in humans and in mouse models of arthritis. Genetically blocking sialylation in activated B cells results in exacerbation of joint inflammation in a collagen-induced arthritis (CIA) model. On the other hand, artificial sialylation of anti-type II collagen antibodies, including ACPAs, not only attenuates arthritogenic activity, but also suppresses the development of CIA in the antibody-infused mice, whereas sialylation of other IgG does not prevent CIA. Thus, our data demonstrate that sialylation levels control the arthritogenicity of RA-associated IgG, presenting a potential target for antigen-specific immunotherapy.

Lactobacillus acidophilus strain L-92 induces apoptosis of antigen-stimulated T cells by modulating dendritic cell function.

Beneficial effects of lactobacilli have been reported for patients with allergic diseases and intestinal disorders such as inflammatory bowel disease. However, it is not fully understood how such bacteria influence the immunologic response. For this purpose, we investigated the effect of Lactobacillus acidophilus strain L-92 (L-92) on antigen-stimulated T cell responses in vitro and in vivo. In vitro, L-92 decreased the proliferation of CD4(+) T cells stimulated with antigen, and also induced apoptosis of antigen-stimulated T cells. On the other hand, interferon (IFN)-gamma secretion from naïve T cells was increased while interleukin (IL)-4 secretion was decreased by L-92. Co-culture with L-92 induced apoptosis of differentiated Th1 and Th2 cells. The degree of apoptosis induction was higher in Th2 cells. Moreover, L-92 up-regulated the expression of B7-H1 and down-regulated that of B7-H2 on dendritic cells (DCs), and DCs exposed to L-92 also induced apoptosis of antigen-stimulated T cells. Finally, orally administered L-92 induced apoptosis of OVA-specific TCR Tg T cells. These results indicate that L-92 attenuates the CD4(+) T cell response by inducing DC-mediated apoptosis and that it might exert beneficial effects in patients with diseases resulting from a hyper-response of CD4(+) T cells.

Hydroxypropyl-β-Cyclodextrin Spikes Local Inflammation That Induces Th2 Cell and T Follicular Helper Cell Responses to the Coadministered Antigen

Cyclodextrins are commonly used as a safe excipient to enhance the solubility and bioavailability of hydrophobic pharmaceutical agents. Their efficacies and mechanisms as drug-delivery systems have been investigated for decades, but their immunological properties have not been examined. In this study, we reprofiled hydroxypropyl-β-cyclodextrin (HP-β-CD) as a vaccine adjuvant and found that it acts as a potent and unique adjuvant. HP-β-CD triggered the innate immune response at the injection site, was trapped by MARCO+ macrophages, increased Ag uptake by dendritic cells, and facilitated the generation of T follicular helper cells in the draining lymph nodes. It significantly enhanced Ag-specific Th2 and IgG Ab responses as potently as did the conventional adjuvant, aluminum salt (alum), whereas its ability to induce Ag-specific IgE was less than that of alum. At the injection site, HP-β-CD induced the temporary release of host dsDNA, a damage-associated molecular pattern. DNase-treated mice, MyD88-deficient mice, and TBK1-deficient mice showed significantly reduced Ab responses after immunization with this adjuvant. Finally, we demonstrated that HP-β-CD–adjuvanted influenza hemagglutinin split vaccine protected against a lethal challenge with a clinically isolated pandemic H1N1 influenza virus, and the adjuvant effect of HP-β-CD was demonstrated in cynomolgus macaques. Our results suggest that HP-β-CD acts as a potent MyD88- and TBK1-dependent T follicular helper cell adjuvant and is readily applicable to various vaccines.

Primary response of naive CD4+ T cells to amino acid-substituted analogs of an antigenic peptide can show distinct activation patterns: Th1- and Th2-type cytokine secretion, and helper activity for antibody production without apparent cytokine secretion

Naive CD4+ T cells differentiate into two types of helper T cells showing an interferon‐γ‐predominant (Th1) or an interleukin‐4‐predominant (Th2) cytokine secretion profile after repeated antigenic stimulation. Their differentiation can be influenced by slight differences in the interaction between the T cell receptor (TCR) and its ligand at the time of primary activation. However, the primary response of freshly isolated naive CD4+ T cells to altered TCR ligands is still unclear. Here, we investigated the primary response of splenic naive CD4+ T cells derived from transgenic mice expressing TCR specific for residues 323–339 of ovalbumin (OVA323–339) bound to I‐Ad molecules. Naive CD4+ T cells secreted either Th1‐ or Th2‐type cytokines immediately after stimulation with OVA323–339 or its single amino acid‐substituted analogs. Helper activity for antibody secretion by co‐cultured resting B cells was also found in the primary response, accompanied by either low‐level Th2‐type cytokine secretion or no apparent cytokine secretion. Our results clearly indicate that dichotomy of the Th1/Th2 cytokine secretion profile can be elicited upon primary activation of naive CD4+ T cells. We also demonstrate that the helper activity of naive CD4+ T cells for antibody production does not correspond to the amounts of the relevant cytokines secreted.