Codevelopment of dendritic cells along with erythroid differentiation from human CD34+ cells by tumor necrosis factor-α

Ineffective erythropoiesis in β -thalassemia

In humans, β-thalassemia dyserythropoiesis is characterized by expansion of early erythroid precursors and erythroid progenitors and then ineffective erythropoiesis. This ineffective erythropoiesis is defined as a suboptimal production of mature erythrocytes originating from a proliferating pool of immature erythroblasts. It is characterized by (1) accelerated erythroid differentiation, (2) maturation blockade at the polychromatophilic stage, and (3) death of erythroid precursors. Despite extensive knowledge of molecular defects causing β-thalassemia, less is known about the mechanisms responsible for ineffective erythropoiesis. In this paper, we will focus on the underlying mechanisms leading to premature death of thalassemic erythroid precursors in the bone marrow.

Delayed addition of tumor necrosis factor (TNF) antagonists inhibits the generation of CD11c+ dendritic cells derived from CD34+ cells exposed to TNF-alpha

We have developed a method that cells exhibiting typical dendritic cell (DC) characteristics are generated from human CD34(+) cells and phagocytose cogenerating erythroid progenitor cells in the presence of tumor necrosis factor-alpha (TNF-alpha), interleukin-3, stem cell factor and erythropoietin. Using this system, we titrated the effects of TNF antagonists, etanercept and infliximab, on TNF-alpha activity. We found that 1 microg/ml etanercept dramatically inhibited the generation of CD11c(+) cells accompanying with a complete recovery of the generation of erythroid progenitors. Infliximab at 200 microg/ml exhibited a similar effect to that observed for etanercept. The delayed addition of etanercept to this culture system at day five resulted in significant inhibitory effects on the generation of CD11c(+), CD4(+) and CD86(+) cells. These results indicate that TNF antagonists administered at a concentration that is achievable in vivo, neutralize the biologic effects of TNF-alpha in generating CD11c(+) cells and that a delay in the administration of these antagonists for as long as 5 days partially inhibits the biologic activity of TNF-alpha. These findings may contribute to a great understanding of anti-TNF therapy in patients with an overproduction of cytokines such as hemophagocytic syndromes.

Phagocytosis of co-developing neutrophil progenitors by dendritic cells in a culture of human CD34(+) cells with granulocyte colony-stimulating factor and tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) has been shown to induce the differentiation of CD34(+) cells toward dendritic cells (DCs). We have previously shown that DCs are co-generated from human CD34(+) cells during erythroid or megakaryocytic differentiation in the presence of TNF-alpha, and those DCs are able to stimulate autologous T cell proliferation. The aim of this study was to learn whether the co-stimulation of granulocyte colony-stimulating factor (G-CSF) and TNF-alpha would generate neutrophil progenitors and DCs together from human CD34(+) cells, and if this was the case, to clarify the phenotypic and functional characteristics of these DCs. When highly purified human CD34(+) cells were cultured for 7 days with G-CSF alone, the generated cells predominantly expressed a granulocyte marker, CD15, and then differentiated into neutrophils after 14 days of culture. The addition of TNF-alpha with G-CSF markedly decreased the number of CD15(+) cells without affecting the total number of cells during 7 days of culture. Almost one third of the generated cells were positive for CD11c and CD123. Furthermore, CD11c(+) cells were found to phagocytose CD15(+) cells and were able to induce allogeneic, but not autologous, T cell proliferation in the mixed lymphocyte reaction (MLR). On the other hand, the CD11c(+) cells generated by TNF-alpha and cytokines capable of inducing erythroid differentiation were able to stimulate autologous T cells. There was a difference in the expression of CD80, CD83 and CD86 among CD11c(+) cells induced by G-CSF plus TNF-alpha and those generated by interleukin-3, stem cell factor, and erythropoietin plus TNF-alpha. These results indicate that the co-stimulation of human CD34(+) cells with G-CSF and TNF-alpha induces the phagocytosis of co-developing neutrophil progenitors by DCs, and the stimulatory effects of these DCs on autologous T cells is different from that of DCs generated from CD34(+) cells during erythroid differentiation.

Phagocytosis of codeveloping megakaryocytic progenitors by dendritic cells in culture with thrombopoietin and tumor necrosis factor-α and its possible role in hemophagocytic syndrome

Tumor necrosis factor-α (TNF-α) and thrombopoietin (TPO) have been shown to induce the differentiation and proliferation of CD34+ cells toward dendritic cells (DCs) in the presence of multiacting cytokines. We hypothesized that the costimulation of TPO and TNF-α generates megakaryocytic progenitors and DCs together from human CD34+ cells and that the interaction of these cells may indicate a physiologic and/or a pathologic role of DCs in megakaryopoiesis. When highly purified human CD34+ cells were cultured for 7 days with TPO alone, the generated cells expressed megakaryocytic markers, such as CD41, CD42b, and CD61. The addition of TNF-α with TPO remarkably decreased the number of megakaryocytic progenitor cells without affecting the cell yield. Almost half of the cells thus generated expressed CD11c, and most of them were positive for CD4 and CD123. Furthermore, CD11c+ cells were found to capture damaged CD61+ cells and to induce autologous T-cell proliferation, although the cytokine productions were low. We also confirmed an engulfment of CD61+ cells and their fragment by CD11c+ cells in bone marrow cells from patients with hemophagocytic syndrome. These findings suggest that DCs generated under megakaryocytic and inflammatory stimuli are involved in megakaryopoiesis and the subsequent immune responses to self-antigens.

TNF Inhibition Rapidly Down-Regulates Multiple Proinflammatory Pathways in Psoriasis Plaques

The mechanisms of action of marketed TNF-blocking drugs in lesional tissues are still incompletely understood. Because psoriasis plaques are accessible to repeat biopsy, the effect of TNF/lymphotoxin blockade with etanercept (soluble TNFR) was studied in ten psoriasis patients treated for 6 months. Histological response, inflammatory gene expression, and cellular infiltration in psoriasis plaques were evaluated. There was a rapid and complete reduction of IL-1 and IL-8 (immediate/early genes), followed by progressive reductions in many other inflammation-related genes, and finally somewhat slower reductions in infiltrating myeloid cells (CD11c+ cells) and T lymphocytes. The observed decreases in IL-8, IFN-gamma-inducible protein-10 (CXCL10), and MIP-3alpha (CCL20) mRNA expression may account for decreased infiltration of neutrophils, T cells, and dendritic cells (DCs), respectively. DCs may be less activated with therapy, as suggested by decreased IL-23 mRNA and inducible NO synthase mRNA and protein. Decreases in T cell-inflammatory gene expression (IFN-gamma, STAT-1, granzyme B) and T cell numbers may be due to a reduction in DC-mediated T cell activation. Thus, etanercept-induced TNF/lymphotoxin blockade may break the potentially self-sustaining cycle of DC activation and maturation, subsequent T cell activation, and cytokine, growth factor, and chemokine production by multiple cell types including lymphocytes, neutrophils, DCs, and keratinocytes. This results in reversal of the epidermal hyperplasia and cutaneous inflammation characteristic of psoriatic plaques.

Supplementation of CXCL12 (CXCL12) induces homing of CD11c+ dendritic cells to the spleen and enhances control of Plasmodium berghei malaria in BALB/c mice

In malaria, parasitaemia is controlled in the spleen, a multicomponent organ that undergoes changes in its cellular constituents to control the parasite. During this process, dendritic cells (DCs) orchestrate the positioning of effector cells in a timely manner for optimal parasite clearance. We have recently demonstrated that CXCL12 [stromal cell-derived factor-1 (CXCL12)] supplementation partially restores the ability to control parasitaemia in Plasmodium berghei-infected mice. In the present study, we investigated the nature of the DCs involved by flow cytometry and immunohistochemistry of CD11c(+) cells. Flow cytometry of bone marrow cells showed that infection with P. berghei did not alter the proportion of CD11c(+) cells present in this haematopoietic compartment, while CXCL12 supplementation of naïve uninfected mice induced only minor increases in the population of CD11c(+) cells. In the spleen, P. berghei infection alone resulted in an increase in CD11c(+) cells as compared with naïve animals. Exogenously administered CXCL12 in the absence of infection resulted in a significant expansion of the splenic CD11c(+) population, and this effect was even more pronounced in infected and supplemented mice. Immunohistochemistry revealed that CD11c(+) cells infiltrated the perivascular areas and marginal zone of the spleen in infected animals treated with CXCL12, suggesting that this chemokine induces homing of CD11c(+) dendritic cells to the splenic compartment. Our results show that small amounts of CXCL12 supplementation are effective in recruiting DCs to the spleens of both uninfected and infected mice, suggesting the participation of CXCL12 and CD11c(+) cells in the establishment of an adequate environment in the spleen for malaria control.