Granzyme A Deficiency Breaks Immune Tolerance and Promotes Autoimmune Diabetes Through a Type I Interferon-Dependent Pathway.

Granzyme A is a protease implicated in the degradation of intracellular DNA. Nucleotide complexes are known triggers of systemic autoimmunity, but a role in organ-specific autoimmune disease has not been demonstrated. To investigate whether such a mechanism could be an endogenous trigger for autoimmunity, we examined the impact of granzyme A deficiency in the NOD mouse model of autoimmune diabetes. Granzyme A deficiency resulted in an increased incidence in diabetes associated with accumulation of ssDNA in immune cells and induction of an interferon response in pancreatic islets. Central tolerance to proinsulin in transgenic NOD mice was broken on a granzyme A-deficient background. We have identified a novel endogenous trigger for autoimmune diabetes and an in vivo role for granzyme A in maintaining immune tolerance.

The pro-apoptotic BH3-only protein Bid is dispensable for development of insulitis and diabetes in the non-obese diabetic mouse.

Type 1 diabetes is caused by death of insulin-producing pancreatic beta cells. Beta-cell apoptosis induced by FasL may be important in type 1 diabetes in humans and in the non-obese diabetic (NOD) mouse model. Deficiency of the pro-apoptotic BH3-only molecule Bid protects beta cells from FasL-induced apoptosis in vitro. We aimed to test the requirement for Bid, and the significance of Bid-dependent FasL-induced beta-cell apoptosis in type 1 diabetes. We backcrossed Bid-deficient mice, produced by homologous recombination and thus without transgene overexpression, onto a NOD genetic background. Genome-wide single nucleotide polymorphism analysis demonstrated that diabetes-related genetic regions were NOD genotype. Transferred beta cell antigen-specific CD8+ T cells proliferated normally in the pancreatic lymph nodes of Bid-deficient mice. Moreover, Bid-deficient NOD mice developed type 1 diabetes and insulitis similarly to wild-type NOD mice. Our data indicate that beta-cell apoptosis in type 1 diabetes can proceed without Fas-induced killing mediated by the BH3-only protein Bid.

NF-κB in type 1 diabetes.

Type 1 diabetes is an autoimmune disease in which pancreatic beta cells are destroyed by autoreactive T cells. It is a common pediatric disease with increasing incidence. Islet transplantation may be a therapeutic option, however, the current limitations of this procedure mean that for most sufferers of type 1 diabetes there is no cure. The transcription factor NF-κB has been widely studied for its role in development of type 1 diabetes. Recent data have shown that NF-κB is required for activation of autoreactive T cells, and its hyperactivity in monocytes and dendritic cells results in altered cytokine secretion and antigen presentation, which ultimately contributes to the initiation of type 1 diabetes. NF-κB is also activated by a number of proinflammatory cytokines to regulate both the survival and death of beta cells. The critical role of NF-κB in type 1 diabetes renders it a promising pharmaceutical target in the intervention of this disease and further understanding of the NF-κB pathway will have an important implication on the development of novel and safe therapeutic strategies.

Abnormal NF-kappa B function characterizes human type 1 diabetes dendritic cells and monocytes.

Dendritic cell (DC) differentiation is abnormal in type 1 diabetes mellitus (T1DM). However, the nature of the relationship between this abnormality and disease pathogenesis is unknown. We studied the LPS response in monocytes and monocyte-derived DCs isolated from T1DM patients and from non-T1DM controls. In T1DM patients, late LPS-mediated nuclear DNA binding by RelA, p50, c-Rel, and RelB was impaired as compared with type 2 DM, rheumatoid arthritis, and healthy subjects, associated with impaired DC CD40 and MHC class I induction but normal cytokine production. In TIDM monocytes, RelA and RelB were constitutively activated, and the src homology 2 domain-containing protein tyrosine phosphatase (SHP-1), a negative regulator of NF-kappaB, was overexpressed. Addition of sodium stibogluconate, a SHP-1 inhibitor, to DCs differentiating from monocyte precursors restored their capacity to respond to LPS in approximately 60% of patients. The monocyte and DC NF-kappaB response to LPS is thus a novel phenotypic and likely pathogenetic marker for human T1DM. SHP-1 is at least one NF-kappaB regulatory mechanism which might be induced as a result of abnormal inflammatory signaling responses in T1DM monocytes.

p38 Mitogen-Activated protein kinase mediates dual role of ultraviolet B radiation in induction of maturation and apoptosis of monocyte-derived dendritic cells.

Although ultraviolet B (UVB) induces apoptosis and functional perturbations in dendritic cells (DC), for example, Langerhans cells (LC), it also stimulates some LC into maturation after irradiation in vivo. To analyze its reciprocal effects on DC, we elucidated the direct effect of UVB on DC in vitro using human monocyte-derived DC (MoDC). UVB from 50 to 200 J per m2 stimulated the maturation of MoDC with (1) augmented expression of CD86 and HLA-DR, (2) enhanced production of IL-1beta, IL-6, IL-8, and TNF-alpha at both the mRNA and protein levels, and (3) enhanced allostimulatory capacity on a per-cell basis, whereas the exceeded doses induced apoptotic cell death. Western-blot analysis of MoDC after UVB demonstrated a concentration-dependent phosphorylation of p38- and c-JUN N-terminal kinase (JNK)-mitogen-activated protein kinases (MAPK), but not that of extracellular signal-regulated kinases. p38 MAPK-inhibitor, SB203580, inhibited both UVB-induced maturation and apoptosis of MoDC. Interestingly, MoDC that had undergone apoptosis exhibited an augmented expression of HLA-DR without upregulation of CD86 antigen, suggesting their tolerogenic phenotype. Thus, our study revealed a dual effect of UVB, to stimulate maturation or to induce apoptosis in MoDC, depending on the dosage, via p38 MAPK pathway.

Interleukin-3 in cooperation with transforming growth factor beta induces granulocyte macrophage colony stimulating factor independent differentiation of human CD34+ hematopoietic progenitor cells into dendritic cells with features of Langerhans cells.

Recently, we have reported that M-CSF in cooperation with TGF-beta1 can induce Langerhans cell (LC) development from hematopoietic progenitor cells (HPCs) without GM-CSF. In the present study, we examined whether TGF-beta1 changes the differentiation of HPCs induced by IL-3 towards LC development. We cultured HPCs in a serum-free medium in the presence of IL-3 and a combination cytokines including Flt3L, SCF, and TNF-alpha with or without TGF-beta1. DCs induced by the IL-3 culture (IL-3 DCs) did not significantly differ from those induced by the GM-CSF culture (GM-CSF DCs). Namely, both expressed CDla, F-cadherin, and Langerin in the presence of TGF-beta1 and stimulated allogeneic T cells at a similar magnitude. In contrast to GM-CSF DCs, IL-3 DCs lacked the expression of Birbeck granules (BGs) in spite of their expression of Langerin. When we compared the expression of Langerin between these two DCs, however, it became clear that both Langerin protein and mRNA were significantly lower in IL-3 DCs than in GM-CSF DCs. These studies again demonstrated the ability of TGF-beta1 to polarize the differentiation of HPCs induced by IL-3 towards LC development, although IL-3 DCs were unable to form BGs partly because of their poor ability to induce Langerin.

p38 Mitogen-activated protein kinase and extracellular signal-regulated kinases play distinct roles in the activation of dendritic cells by two representative haptens, NiCl2 and 2,4-dinitrochlorobenzene.

Previous studies have demonstrated that haptens induce several phenotypic and functional changes of dendritic cells in vivo as well as in vitro. Although recently, the crucial role of p38 mitogen-activated protein kinase has been reported in the activation of dendritic cells by haptens, the signal transduction elements involved in each phenotypic and functional changes that occur in the activation of dendritic cells by haptens remain unknown. Therefore, we examined the role of mitogen-activated protein kinases and nuclear factor-kappaB in the signal transduction of dendritic cells stimulated with two representative haptens, i.e., NiCl2 and 2,4-dinitrochlorobenzene. Human monocyte-derived dendritic cells stimulated with 2,4-dinitrochlorobenzene induced the phosphorylation of p38 and stress-activated protein kinase/c-jun N-terminal kinases, whereas NiCl2 induced that of p44/42 extracellular signal-regulated kinases, p38, and stress-activated protein kinase/c-jun N-terminal kinases. In addition, NiCl2 phosphorylated inhibitor kappaB and activated nuclear factor-kappaB. In contrast, primary irritants, e.g., benzalkonium chloride, or sodium lauryl sulfate, did not activate these signal transduction pathways. By using specific inhibitors for extracellular signal-regulated kinases and p38 pathways, PD98059 and SB203580, respectively, we demonstrated that the augmentation of CD86, HLA-DR, and CD83, and the production of interleukin-8 along with its increased mRNA expression by monocyte-derived dendritic cells stimulated with 2,4-dinitrochlorobenzene, and the augmentation of CD83 and the interleukin-12 p40 production by monocyte-derived dendritic cells stimulated with NiCl2, were suppressed by SB203580, whereas PD98059 suppressed the production of interleukin-1beta and tumor necrosis factor-alpha, together with their increased mRNA expression by monocyte-derived dendritic cells treated with NiCl2. On the other hand, in spite of the activation of nuclear factor-kappaB by monocyte-derived dendritic cells stimulated with NiCl2, nuclear factor-kappaB inhibitor did not significantly affect the phenotypic and functional changes in the activation of monocyte-derived dendritic cells. These data indicate that NiCl2 and 2,4-dinitrochlorobenzene stimulate different signal transduction pathways in monocyte-derived dendritic cells, and subsequently induce different phenotypic and functional changes in them.

Macrophage colony-stimulating factor in cooperation with transforming growth factor-beta1 induces the differentiation of CD34+ hematopoietic progenitor cells into Langerhans cells under serum-free conditions without granulocyte-macrophage colony-stimulating factor.

Macrophage colony-stimulating factor has not been considered as a factor responsible for dendritic cell or Langerhans cell development from hematopoietic progenitor cells. In this study, we examined whether macrophage colony-stimulating factor could be used instead of granulocyte-macrophage colony-stimulating factor for the in vitro development of Langerhans cells from hematopoietic progenitor cells. We replaced granulocyte-macrophage colony-stimulating factor with macrophage colony-stimulating factor from a serum-free culture containing granulocyte-macrophage colony-stimulating factor, stem cell factor, Flt3 ligand, tumor necrosis factor-alpha, and transforming growth factor-beta1. This serum-free culture medium containing macrophage colony-stimulating factor, but not granulocyte-macrophage colony-stimulating factor (macrophage colony-stimulating factor culture), could induce CD1a+ Birbeck granule+ Langerin+ E-cadherin+ factor-like XIIIa Langerhans cells. As a control, the culture of hematopoietic progenitor cells in this culture medium depleted of macrophage colony-stimulating factor or transforming growth factor-beta1 resulted in far fewer or null CD1a+ cells, respectively. Macrophage colony-stimulating factor increased the number of CD1a+ cells in a concentration-dependent fashion. These macrophage colony-stimulating factor-induced Langerhans cells were different from granulocyte-macrophage colony-stimulating factor-induced Langerhans cells in their decreased expression of CD11c and their immature phenotype. The decreased expression of CD11c, however, was recovered by culturing them with granulocyte-macrophage colony-stimulating factor, while they acquired a mature phenotype qby granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, interleukin-1alpha, or lipo-polysaccharide. Macrophage colony-stimulating factor-induced Langerhans cells could stimulate allogeneic T cells. Interestingly, we could keep the growth and immature phenotypes of macrophage colony-stimulating factor-induced Langerhans cells for at least 28 d of culture. These studies demonstrated that macrophage colony-stimulating factor in cooperation with transforming growth factor-beta1 could induce Langerhans cell development from hematopoietic progenitor cells in vitro without granulocyte-macrophage colony-stimulating factor, which suggests the possibility that macrophage colony-stimulating factor plays a part in the Langerhans cell development in vivo. In addition, the culture using macrophage colony-stimulating factor presents a novel culture system to enable a large-scale and long-term culture of immature Langerhans cells.

H1 and H2 histamine receptors are absent on Langerhans cells and present on dermal dendritic cells.

Human monocyte-derived dendritic cells (MoDC) have both histamine H1 and H2 receptors and can induce CD86 expression by histamine. Nevertheless, it has not been reported whether human epidermal Langerhans cells (LC) have histamine receptors or not. In this study, using RT-PCR, we investigated the expression of H1 and H2 receptor mRNA on DC with the features of LC (LC-like DC) that were generated in vitro from peripheral blood monocytes, LC derived from CD34+ hematopoietic progenitor cells, and LC obtained from human epidermis. We compared the histamine-induced CD86 expression among these cells. In contrast to MoDC, LC and LC-like DC did not express H1 or H2 receptors. In addition, they could not augment the CD86 expression by histamine. Interestingly, when transforming growth factor-beta1 (TGF-beta1) was added to the culture of MoDC, the expression of H1 and H2 receptors and the histamine-induced CD86 expression were abrogated in a concentration-dependent fashion. Finally, in the assessment of the cell surface expression of histamine receptors using fluorescence-labeled histamine, histamine could bind to MoDC and dermal dendritic cells obtained from the skin, whereas there was no specific binding of histamine to LC-like DC or LC obtained from the skin. These data suggest that LC do not express either H1 or H2 receptors, mainly because of the effect of TGF-beta1. This made a striking contrast with the expression of the functional H1 and H2 receptors on MoDC and dermal dendritic cells.

Cord blood CD34+ cells differentiate into dermal dendritic cells in co-culture with cutaneous fibroblasts or stromal cells.

The skin is a unique organ that contains two different subsets of dendritic cells, i.e., Langerhans cells and dermal dendritic cells. Our hypothesis is that cutaneous fibroblasts may affect the development of these dendritic cells. We cocultured cord blood CD34+ hematopoietic progenitor cells with several human cutaneous fibroblast cell lines without any exogenous cytokines for 3 wk. In this culture, hematopoietic progenitor cells increased in number from 20.1 +/- 2.4 times, and produced aggregates of cells with dendritic processes. They were composed of 54.9 +/- 3.2% HLA-DR+ CD14+ CD1a-- cells and 13.8 +/- 3.6% HLA-DR+ CD1a+ cells, which also expressed CD11b and CD11c. There were significant numbers of factor XIIIa+ cells in the culture, whereas no Lag+ or E-cadherin+ cells were detected, and they were potent stimulators in allogeneic T cell activation. There was a significant difference in the ability to induce CD1a+ cells among different human cutaneous fibroblast cell lines. These CD1a+ cells lacked the expression of CD80, CD86, or CD83. In addition, half of them still expressed CD14. When these dendritic cells were cultured with tumor necrosis factor-alpha, however, they became mature dendritic cells with augmented expression of CD86 and CD83 and with increased allogeneic T cell stimulation. The subsequent experiment using a dividing chamber, enzyme-linked immunosorbent assay for granulocyte-macrophage colony-stimulating factor and macrophage colony-stimulating factor, and the blocking studies with antibodies for these cytokines suggested that both the presence of direct contact between hematopoietic progenitor cells and human cutaneous fibroblast cell lines and macrophage colony-stimulating factor produced by human cutaneous fibroblast cell lines are required for their maximum growth and differentiation into CD1a+ dendritic cells, whereas macrophage colony-stimulating factor was solely responsible for their differentiation. These data suggest that cutaneous fibroblasts support the differentiation of dermal dendritic cells in addition to that of monocytes from hematopoietic progenitor cells by their direct contact with hematopoietic progenitor cells and by their macrophage colony-stimulating factor production.