Phenotype and function of GM-CSF independent dendritic cells generated by long-term propagation of rat bone marrow cells

GM-CSF is believed to be an essential factor for growth and differentiation of myeloid dendritic cells (DC). Employing a low-density fraction of rat bone marrow cells, we attempted to generate DC with human Flt-3/Flk-2 and IL-6. In this culture system, typical DC gradually appeared without exogenous GM-CSF supplement. Phenotypes and functions of the DC were examined. Evidence provided that the most efficient long-term outgrowth of DC progenitors was obtained by GM-CSF independent culture systems with the aid of Flt3/Flk-2 and IL-6, not with c-kit ligand and IL-6. Furthermore, CD103 (OX-62), which is widely used for rat DC separation, was found to be insufficient for enriching DC, due to the down-regulation of the marker. However, the most efficient selection of rat DC was made by CD161a (NKR-P1A), a C-type lectin family. The GM-CSF independent DC was functionally active in vitro as well as in vivo assays.

Kit and FcepsilonRI mediate unique and convergent signals for release of inflammatory mediators from human mast cells

In human mast cells, derived from CD34(+) peripheral blood cells, we observed that Kit ligand (KL) failed to induce degranulation but acted in synergy with antigen to markedly enhance degranulation, levels of cytokine gene transcripts, and production of cytokines. Further examination revealed that antigen and KL activated common and unique signaling pathways to account for these varied responses. KL, unlike antigen, failed to activate protein kinase C but activated phospholipase Cgamma and calcium mobilization and augmented these signals as well as degranulation when added together with antigen. Both KL and antigen induced signals that are associated with cytokine production, namely phosphorylation of the mitogen-activated protein kinases, phosphatidylinositol 3-kinase-dependent phosphorylation of protein kinase B (also known as Akt), and phosphorylation of nuclear factor kappaB (NFkappaB). However, only KL stimulated phosphorylation of signal transducer and activator of transcription 5 (STAT5) and STAT6, whereas antigen weakly stimulated the protein kinase C-dependent induction and phosphorylation of c-Jun and associated activating protein-1 (AP-1) components, an action that was markedly potentiated by costimulation with KL. Interestingly, most signals were down-regulated on continuous exposure to KL but were reactivated along with cytokine gene transcription on addition of antigen. The findings, in total, indicated that a combination of FcepsilonRI and Kit-mediated signals and transcriptional processes were required for optimal physiologic responses of human mast cells to antigen.

Inhibition of stem cell factor reduces pulmonary cytokine levels during allergic airway responses

Stem cell factor (SCF) has a significant role in the inflammation and activation of allergic airway responses. When monoclonal anti-SCF was administered intratracheally during allergen challenge there was a significant alteration of eosinophil accumulation and airway hyperreactivity (AHR). Anti-SCF treatment also attenuated pulmonary cytokine and chemokine levels. In particular, there was an antibody dose-dependent decrease in interleukin (IL)-5 and tumour necrosis factor (TNF)-alpha. There was also a significant reduction of CCL2 and CCL5, which correlated with the reduction in AHR. Mice treated with anti-SCF demonstrated a significant decrease in pulmonary gob-5 gene expression, which has been shown to correlate to goblet cell hyperplasia/metaplasia relating to airway mucus production. Blocking SCF-mediated activation within the airway using a monoclonal antibody indicates that this cytokine may represent a viable target for therapeutic intervention that could affect multiple aspects of allergen-induced immunopathology.

Recombinant human (rh) stem cell factor and rhIL-4 stimulate differentiation and proliferation of CD3+ cells from umbilical cord blood and CD3+ cells enhance FcepsilonR1 expression on fetal liver-derived mast cells in the presence of rhIL-4

We previously reported that rhIL-4 induced apoptosis and rhIL-6 mediated protection of human mast cells derived from cord blood mononuclear cells. Based on the result, we attempted to obtain the phenotypes and differentiation of CD3+ cells from cord blood by investigating their cell surface markers in the presence of rhSCF plus rhIL-4. The effect of co-cultured CD3+ cells on fetal liver mast cells (FLMCs) was also determined. Phenotypes from cord blood-derived cells were analyzed by flow cytometry and cell numbers were determined. Fetal liver mast cells were cultured with cord blood-derived cells (mainly CD3+) in the presence of rhSCF and/or rhIL-4 and were analyzed to determine cell number and expression of Kit+ and FcepsilonR1. The percentage of CD3+ cells from cord blood-derived cells on day 0 was about 41 +/- 13.5%, following monocytes and granulocytes. CD3+ cells increased in number (1.5-fold) and purity (90%), whereas other cell types did not survive. More than 60% of CD3+ cells from cord blood at day 0 were CD4(-)CD8-. These double-negative cells dramatically decreased by 1 week of culture, while CD4+CD8+ cells increased in number and purity through 3 weeks of culture, and then decreased as greater numbers of single-positive T cells emerged. We also found that FcepsilonR expression on FLMC increased in the presence of rhIL-4, but was not affected by the T cells that developed from cord blood mononuclear cells. The results indicate that IL-4, a Th2 type cytokine, together with rhSCF, can induce T cell proliferations, differentiation, and maturation from cord blood progenitor cells.

NTAL phosphorylation is a pivotal link between the signaling cascades leading to human mast cell degranulation following Kit activation and Fc epsilon RI aggregation

Aggregation of high-affinity receptors for immunoglobulin E (Fc epsilon RI) on the surface of mast cells results in degranulation, a response that is potentiated by binding of stem cell factor (SCF) to its receptor Kit. We observed that one of the major initial signaling events associated with Fc epsilon RI-mediated activation of human mast cells (HuMCs) is the rapid tyrosine phosphorylation of a protein of 25 to 30 kDa. The phosphorylation of this protein was also observed in response to SCF. This protein was identified as non-T-cell activation linker (NTAL), an adaptor molecule similar to linker for activated T cells (LAT). Unlike the Fc epsilon RI response, SCF induced NTAL phosphorylation in the absence of detectable LAT phosphorylation. When SCF and antigen were added concurrently, there was a marked synergistic effect on NTAL phosphorylation, however, SCF did not enhance the phosphorylation of LAT induced by Fc epsilon RI aggregation. Fc epsilon RI- and SCF-mediated NTAL phosphorylation appear to be differentially regulated by Src kinases and/or Kit kinase, respectively. Diminution of NTAL expression by silencing RNA oligonucleotides in HuMCs resulted in a reduction of both Kit- and Fc epsilon RI-mediated degranulation. NTAL, thus, appears to be an important link between the signaling pathways that are initiated by these receptors, culminating in mast cell degranulation.

Colony-Stimulating Activity of Fetal Liver Cells: Synergistic Role of Stem Cell Factor in Bone Marrow Recovery from Aplastic Anemia

Previously, we and others have shown that fetal liver infusion (FLI) leads to autologous hematopoietic improvement in 40-54% of patients with aplastic anemia. However, whether this recovery was spontaneous or the effect of the infused liver cells was not clear. To dissect the role of FLI in autologous hematopoietic recovery, the colony-supporting potential of fetal liver-conditioned medium (FLCM) was evaluated in bone marrow (BM) cells of normal adult and aplastic anemia patients. In both cases, each sample of FLCM supported the growth of colony-forming cells in semi solid culture medium. The FLCM was assayed for the presence of four principal colony-stimulating cytokines, namely stem cell factor (SCF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and erythropoietin (Epo). While GM-CSF, IL-3, and Epo were present in insignificant amounts or were altogether absent, 50-635 pg/ml of SCF was found in 8 of the 13 FLCM samples tested. Preliminary results of bioneutralization assay indicated the possible role of SCF, secreted by the FL cells, in colony-supporting activity of aplastic anemia and normal BM cells. Overall, our in vitro study implicates the paracrine role of infused FL cells in regenerating autologous hematopoiesis in aplastic anemia patients.

IgE alone stimulates mast cell adhesion to fibronectin via pathways similar to those used by IgE + antigen but distinct from those used by Steel factor

We recently demonstrated that immunoglobulin E (IgE), in the absence of cross-linking agents, activates signaling pathways in healthy murine bone marrow-derived mast cells (BMMCs) and that this activation enhances BMMC survival, at least in part, via secretion of autocrine-acting cytokines. We report herein that IgE alone also triggers the adhesion of both BMMCs and connective tissue mast cells (CTMCs) to the connective tissue component, fibronectin (FN). This adhesion occurs to the same extent as that triggered by optimal levels of Steel factor (SF) or IgE + antigen (IgE + Ag) and is mediated by an increased avidity of the integrin very late antigen 5 (VLA-5). Moreover, this IgE-induced adhesion, which is prolonged compared with that elicited by SF or IgE + Ag, requires phosphatidylinositol 3-kinase (PI3K), phospholipase C gamma (PLCgamma), and extracellular calcium but not extracellular-regulated kinase (Erk) or p38. Interestingly, we found, using the calcium channel blocker, 2-APB (2-aminoethoxydiphenyl borate) and Lyn-/- BMMCs that both IgE- and IgE + Ag-induced adhesion to FN require extracellular calcium entry, whereas SF does not. Furthermore, our data suggest that FN acts synergistically with IgE to prolong intracellular phosphorylation events and to enhance IgE-induced inflammatory cytokine production and BMMC survival.

Circulating stem cell factor in patients with chronic idiopathic urticaria

BACKGROUND

The nature of histamine-releasing factors involved in the pathogenesis of chronic idiopathic urticaria (CIU) is still controversial, since functional IgG autoantibodies specific for the high-affinity IgE receptor, Fc(epsilon)RI, can be detected in only 20% of patients showing a strong skin reactivity on the autologous serum skin test. The absence of systemic eosinophilia in CIU patients, along with the increase in mast cells in skin biopsy specimens, suggests a possible role for stem cell factor (SCF), the only cytokine/growth factor known to induce mediator release from human mast cells.

OBJECTIVE

To investigate the possible role of SCF as a histamine-releasing factor in patients with CIU.

METHODS

The SCF levels were measured in serum samples from 65 patients with CIU who scored strongly positive on the autologous serum skin test; of these patients, 32 had negative results and 33 had positive results on in vitro histamine release assay by a quantitative commercial sandwich immunoassay technique. Serum samples from 40 healthy subjects were used as controls.

RESULTS

Serum SCF levels in all 65 CIU patients did not differ from those found in healthy controls. No difference in SCF levels was found between patients with positive and negative results on histamine release assay.

CONCLUSIONS

An increase in serum SCF levels does not play a pathogenic role in CIU.

Cytokines, including stem cell factor alone, enhance lentiviral transduction in nondividing human LTCIC and NOD/SCID repopulating cells

Hematopoietic stem cells (HSC) require extensive cytokine-mediated stimulation and proliferation for efficient transduction by oncoretroviral vectors. Since lentiviral vectors can transduce nondividing cells, the need for cytokine stimulation has been questioned. We studied HIV-based lentiviral transduction of human early hematopoietic progenitors from umbilical cord blood in the presence or absence of IL-3, IL-6, stem cell factor (SCF), and Flt-3L (36SF) or SCF alone and characterized the effects of these conditions on the stem cell phenotype. Gene transfer was significantly higher in the presence of 36SF in mass culture cells, CFC, LTCIC, and NOD/SCID repopulating cells (SRC). Transduction of primitive progenitor/stem cells was poor without cytokines, with only 12% LTCIC and 23% SRC transduced, compared to 59% in LTCIC and 81% in SRC with 36SF. SCF alone matched transduction rates of multiple cytokines with 70% in CFC. Cytokines prevented apoptosis, expanded CD34(+) cell number, and maintained CFC and LTCIC frequencies. Cytokine stimulation increased transduction of nondividing Ara-C-resistant and aphidicolin-inhibited cells similar to dividing cells. These data suggest that cytokines enhance lentiviral transduction of HSC, without requiring cell division, and maintain the stem cell phenotype. SCF stimulation alone was sufficient for high level transduction.

Stem cell factor attenuates liver damage in a murine model of acetaminophen-induced hepatic injury

Acute liver injury is a common cause of intensive care unit visits. In these studies, we used a murine model of acetaminophen poisoning to examine the role of stem cell factor (SCF) on liver damage. In the initial studies, we identified that the liver produces relatively high constitutive levels of SCF. Upon administration of acetaminophen, the levels of SCF fell dramatically, correlating to damage within the liver. When the liver was allowed to regenerate, the levels of SCF again correlated with the liver regeneration. We next treated mice with anti-SCF before sublethal doses of acetaminophen and significantly increased lethality in anti-SCF-treated animals. When exogenous SCF was given to mice, the lethality was significantly reduced compared with the control acetaminophen-treated animals and the damage within the liver tissue was attenuated. The administration of rSCF reduced the level of steady-state mRNA for cytochrome P450 cyp2E1 enzyme both in vitro and in vivo. These data suggest that SCF functions as an important factor that protects livers from acute damage.

Cytokines and the immune-testicular axis

Cytokines are regulatory proteins involved in haematopoiesis, immune cell development, inflammation and immune responses. Several cytokines have direct effects on testicular cell functions, and a number of these are produced within the testis even in the absence of inflammation or immune activation events. There is compelling evidence that cytokines, in fact, play an important regulatory role in the development and normal function of the testis. Pro-inflammatory cytokines including interleukin-1 and interleukin-6 have direct effects on spermatogenic cell differentiation and testicular steroidogenesis. Stem cell factor and leukaemia inhibitory factor, cytokines normally involved in haematopoiesis, also play a role in spermatogenesis. Anti-inflammatory cytokines of the transforming growth factor-beta family are implicated in testicular development. Consequently, local or systemic up-regulation of cytokine expression during injury, illness or infection may contribute to the disruption of testicular function and fertility that frequently accompanies these conditions. The aim of this review is to provide a very brief summary of the extensive literature dealing with cytokines in testicular biology, and to follow this with some speculation concerning the significance of these molecules in interactions between the immune system and the testis.

Rapid and efficient generation of lentivirally gene-modified dendritic cells from DC progenitors with bone marrow stromal cells

Since dendritic cells (DC) play pivotal roles in both innate and adaptive immunity, DC can be a good target for immuno-gene therapy. However, the optimal generation method for gene-modified DC has not yet been well exploited. CD34+ cells from cord blood (CB), bone marrow (BM), or peripheral blood (PB) were expanded in a medium containing stem cell factor (SCF), flt 3 ligand (Flt3L) and thrombopoietin (TPO) with or without HESS-5, a murine BM stromal cell line, for 2 weeks (the first expansion step), then differentiated to DC in a medium containing granulocyte-macrophage colony-stimulating factor (GM-CSF), flt 3 ligand (Flt3L), stem cell factor (SCF), tumor necrosis factor-alpha (TNF-alpha), IL-4, and lipopolysaccharide (LPS) for 9 days (the second differentiation step). DC progenitors were transduced with human immunodeficiency virus (HIV) vectors at different time points during the second step. Use of HESS-5 during the first step resulted in more DC generation than without it (cell expansion: CB, 10,461 vs. 354-fold; BM, 962 vs. 225-fold; peripheral blood mononuclear cell (PBMC), 8,506 vs. 240-fold; %DC: CB, 83.4% vs. 76.9%; BM, 83.6 vs. 69.8%; PBMC, 85.9 vs. 60.5%). Gene transduction to the in vitro expanded DC progenitors at day 3 during the second step, resulted in better final yield of the gene-modified DC than that to those at day 0 or day 6 (as much as 44% of DC expressed green fluorescence protein (GFP) as a transgene) and the transduction efficiency correlated with endocytic ability and percent of S phase. DC transduced with an HIV vector encoding a melanoma antigen, MART-1, were adequately recognized by specific anti-MART-1 CTL. The two-step culture method with HESS-5 is useful for rapid expansion of DC progenitors and subsequent lentiviral gene transduction to DC.

Production of a monoclonal antibody that recognizes bovine stem cell factor (SCF) and its use in the detection and quantitation of native soluble bovine SCF in fetal bovine serum

Stem cell factor (SCF) is a pluritropic hematopoietic cytokine that acts predominantly on the proliferation and differentiation of hematopoietic progenitor cells. SCF has long been thought to be present in fetal bovine serum (FBS) as an endogenous factor that stimulates the growth of hematopoietic progenitor cells in FBS-supplemented cultures. To detect and quantitate bovine SCF in FBS, we produced a monoclonal antibody (mAb) by immunizing mice with recombinant soluble bovine SCF protein, which was expressed in insect cells by using a baculovirus system. Using the mAb, we purified native soluble bovine SCF from FBS by immunoaffinity chromatography. Western blot analysis revealed that the purified SCF protein had a molecular weight of 33 kDa. In addition, an enzyme-linked immunosorbent assay (ELISA) incorporating the mAb revealed that the levels of native soluble SCF in commercially available FBS were likely to be <100 pg/ml. These results suggest that the concentration of native soluble bovine SCF present in FBS may be insufficient to promote additive biologic effects on the growth of hematopoietic progenitor cells in FBS-supplemented cultures.

Intestinal mast cell progenitors require CD49dbeta7 (alpha4beta7 integrin) for tissue-specific homing

Mast cells (MCs) are centrally important in allergic inflammation of the airways, as well as in the intestinal immune response to helminth infection. A single lineage of bone marrow (BM)-derived progenitors emigrates from the circulation and matures into phenotypically distinct MCs in different tissues. Because the mechanisms of MC progenitor (MCp) homing to peripheral tissues have not been evaluated, we used limiting dilution analysis to measure the concentration of MCp in various tissues of mice deficient for candidate homing molecules. MCp were almost completely absent in the small intestine but were present in the lung, spleen, BM, and large intestine of beta7 integrin-deficient mice (on the C57BL/6 background), indicating that a beta7 integrin is critical for homing of these cells to the small intestine. MCp concentrations were not altered in the tissues of mice deficient in the alphaE integrin (CD103), the beta2 integrin (CD18), or the recombination activating gene (RAG)-2 gene either alone or in combination with the interleukin (IL)-receptor common gamma chain. Therefore, it is the alpha4beta7 integrin and not the alphaEbeta7 integrin that is critical, and lymphocytes and natural killer cells play no role in directing MCp migration under basal conditions. When MCp in BALB/c mice were eliminated with sublethal doses of gamma-radiation and then reconstituted with syngeneic BM, the administration of anti-alpha4beta7 integrin, anti-alpha4 integrin, anti-beta7 integrin, or anti-MAdCAM-1 monoclonal antibodies (mAbs) blocked the recovery of MCp in the small intestine. The blocking mAbs could be administered as late as 4 d after BM reconstitution with optimal inhibition, implying that the MCp must arise first in the BM, circulate in the vasculature, and then translocate into the intestine. Inasmuch as MCp are preserved in the lungs of beta7 integrin-deficient and anti-alpha4beta7 integrin-treated mice but not in the small intestine, alpha4beta7 integrin is critical for tissue specific extravasation for localization of MCp in the small intestine, but not the lungs.

Mast cell distribution and activation in chronic pancreatitis

Chronic pancreatitis (CP) is characterized by mononuclear inflammatory cell infiltration and replacement of the destroyed parenchyma by fibrous tissue. Recently, mast cells have been implicated in chronic inflammatory processes with fibrous tissue deposition. Therefore, the number and distribution of mast cells and their state of activation were evaluated in 12 normal specimens and in 46 specimens of CP with different causes (alcoholic, tropical, and idiopathic). Furthermore, the presence of stem cell factor (SCF), the main mast cell growth factor, and of its receptor, c-kit, was also assessed. In CP tissues, mast cells were localized both in the fibrotic areas and in the residual acinar parenchyma. The total number of mast cells was significantly higher in CP than in the normal pancreas (P < .0001) and correlated positively with the extent of fibrosis and the intensity of inflammation. Immunoglobulin E (IgE)-dependent mast cell activation was higher in CP than in the normal pancreas. No differences in mast cell number or IgE positivity were found among the 3 causes of CP. SCF-and c-kit immunoreactive mast cells were mostly localized in fibrous tissue and around regenerating ducts, which were also positive for c-kit but were negative for SCF. These results suggest that mast cells, activated by an IgE-dependent mechanism and/or by an SCF-c-kit autocrine loop, are a relevant component of the inflammatory infiltrate in CP, independent of the underlying cause. Their localization near degenerating acini and regenerating ducts might indicate that they play a crucial role in tissue destruction and remodeling in CP.

Steel factor sustains SCL expression and the survival of purified CD34+ bone marrow cells in the absence of detectable cell differentiation

CD34+ cells express the basic helix-loop-helix transcription factor SCL, which is essential for blood cell formation in vivo. In addition, their survival is critically dependent on hemopoietic growth factors. We therefore compared the effects of Steel factor (SF) and GM-CSF on the survival, proliferation, and differentiation of primary human CD34+ cells, as well as the role of SCL during these processes. GM-CSF suppresses apoptosis in CD34+ cells, which proliferate and differentiate into mature granulocytic and monocytic cells (CD34-CD13+) and loose SCL expression. In contrast, SF suppresses apoptosis without a significant increase in cell numbers, and the cells remain CD34+ and SCL+ with a blast-like morphology. Examination of apoptosis by the terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) reaction and of the cell cycle status indicated that SF is both a survival factor and a mitogenic factor for CD34+ cells. There was, however, constant cell death in a fraction of the population, which could be rescued by GM-CSF. Co-addition of SF and GM-CSF prevents the downregulation of SCL observed in the presence of GM-CSF by itself, allows for prolonged survival and expansion of CD34+ cells in culture, inhibits monocytic differentiation and impairs granulocytic differentiation. Finally, exposure to an antisense SCL but not a control oligonucleotide decreases SCL protein levels and prevents the suppression of apoptosis by SF without affecting GM-CSF-dependent cell survival. These observations suggest that the hemopoietic transcription factor SCL regulates the survival of CD34+ cells in response to SF.

The paracrine role of stem cell factor/c-kit signaling in the activation of human melanocytes in ultraviolet-B-induced pigmentation

The interaction of stem cell factor with its receptor, c-kit, is well known to be critical to the survival of melanocytes. Little is known about the role(s) of the stem cell factor/c-kit interaction in epidermal pigmentation, however. To clarify whether the stem cell factor/c-kit signaling has a paracrine role in ultraviolet-B-induced pigmentation, we determined whether the exposure of human keratinocytes, melanocytes, and the epidermis to ultraviolet B light stimulates the expression of stem cell factor or c-kit at the gene and/or protein levels. We further examined whether interrupting the binding of stem cell factor to c-kit by subepidermal injection of a monoclonal antibody to c-kit affects ultraviolet-B-induced pigmentation in brownish guinea pig skin. When human keratinocytes and melanocytes in culture were exposed to ultraviolet B light, transcripts of stem cell factor and c-kit (as assessed by reverse transcription polymerase chain reaction) and expression of those proteins (by enzyme-linked immunosorbent assay and western blotting) increased significantly and peaked at a dose of 20-40 mJ per cm2. In ultraviolet-B-exposed human epidermis, stem cell factor transcripts and protein expression were also markedly enhanced compared with the nonexposed epidermis. Immunohistochemistry with antibodies to stem cell factor revealed an increased staining in the ultraviolet-B-exposed epidermis, which was accompanied by a slight epidermal hyperplasia. In the course of ultraviolet-B-induced pigmentation of brownish guinea pig skin, the subepidermal injection of c-kit inhibitory antibodies completely abolished the induction of pigmentation in the ultraviolet-B-exposed area, and there was no increase in the number of dihydroxyphenylalanine-positive melanocytes. These findings indicate that the stem cell factor/c-kit signaling is critically involved in the biologic mechanism of ultraviolet-B-induced pigmentation.

Regulation of T cell cytokine production by dendritic cells generated in vitro from hematopoietic progenitor cells

When dendritic cells (DC) present antigens to T cells, reciprocal cellular interactions occur that lead to cytokine production. This cytokine response is regulated by specific properties of DC, notably their maturation/activation status and perhaps their origin. The latter possibility prompted us to determine if DC produced along distinct developmental pathways induced distinct T cell responses. Hematopoietic progenitor cells with the potential to differentiate into multiple lineages of cells were induced to differentiate into DC along two pathways. One leads to the formation of lymphoid-related DC but not of monocyte-derived DC and is induced by culture of CD34(+) cells with flt-3 ligand (F), c-kit ligand (K), GM-CSF (Gm), IL-1beta ("1"), and IL-7 ("7") (FKGm17). Another pathway with distinct molecular requirements supports in part monocyte-derived DC and is induced by the cytokines F, K, Gm, TNF-alpha (T), and IL-4 ("4") (FKGmT4). DC produced along these two pathways were isolated by flow cytometry and compared. They differed only slightly in phenotype and morphology and both induced Th1-type cytokine production in MLR (mixed lymphocyte reactions). However, on a cell-per-cell basis, FKGm17-DC produced more IL-18 or IL-12 and induced more IFN-gamma by T cells in MLR. Such superior properties were not intrinsically determined by the origin of the DC but were induced by FKGm17 cytokines. We conclude that lymphoid-related DC have the potential to induce Th1 T cell responses but that environmental signals strongly influence T-cell-stimulating properties of DC.

Expression of Kit, the receptor for stem cell factor, in bovine peripheral blood

The expression of Kit, the receptor for stem cell factor (SCF), on bovine peripheral blood cells (PBCs) was examined by using monoclonal antibodies against the bovine Kit protein. Flow cytometric analysis showed that approximately 1.5% of PBCs expressed Kit. In cytospin preparations, the morphology of most Kit+ PBCs was similar to that of large lymphocytes. Subsets of Kit+ PBCs coexpressed CD3, IgM, and/or CD11b but not CD14 or G1. SCF did not induce the proliferation of Kit+ PBCs in vitro. These results indicate that Kit is expressed on subsets of lymphocytes in bovine peripheral blood, but the ligand of Kit, SCF, does not directly induce the proliferation of this cell population.

Demonstration of mast cell chemotactic activity in synovial fluid from rheumatoid patients

OBJECTIVES

The significance of the mast cell in the pathogenesis of rheumatic diseases has become more evident. Although mast cell hyperplasia is a feature of rheumatoid arthritis, the nature of mast cell chemoattractants involved in the recruitment of mast cells in joint diseases has not been studied in any detail. In this study the presence of mast cell chemotactic activity in synovial fluids was examined.

METHODS

Synovial fluids from seven rheumatoid patients were tested in a modified Boyden chamber, where a human mast cell line was used as responder. The presence of stem cell factor (SCF) and transforming growth factor beta (TGFbeta) was measured by enzyme linked immunosorbent assay (ELISA).

RESULTS

Six of the seven synovial fluids tested exhibited mast cell chemotactic activity. Two characterised human mast cell chemotaxins, SCF and TGFbeta, were highly expressed in the synovium. Soluble SCF could be detected in all fluids analysed. Blocking antibodies against SCF or TGFbeta almost completely blocked the activity in one fluid, partially blocked the activity in three, and did not affect the activity in two. Treatment of the responder cells with pertussis toxin reduced the migratory response against seven fluids, indicating the presence of chemoattractants mediating their effect through G(i) coupled receptors.

CONCLUSION

These data demonstrate the presence of multiple factors in synovial fluid acting as mast cell chemoattractants, two of which are SCF and TGFbeta that contribute to the effect. These findings may be of importance for developing new strategies to inhibit mast cell accumulation in rheumatic diseases.

Relationship between interstitial cells of Cajal and enteric motor neurons in the murine proximal colon

Interstitial cells of Cajal (ICC) are interposed between enteric neurons and smooth muscle cells in gastrointestinal (GI) muscles. The specific relationships between these cells in the murine proximal colon were studied with conventional and immunoelectron microscopy and immunohistochemistry. Intramuscular interstitial cells (IC-IM) formed discrete networks within the circular muscle layer of the murine proximal colon. Nerve trunks ran in close association with IC-IM and individual nerve trunks came into close contact with multiple IC-IM. Conventional electron microscopy revealed very close (< or = 20 nm) associations between nerve fibers and IC-IM. Processes of IC-IM also formed close contacts with neighboring smooth muscle cells. At the points of close association between neurons and IC-IM, areas of membrane densification in both pre- and postjunctional cells were present, suggesting specialized contacts or synaptic-like structures. Similar points of contact between neurons and smooth muscle cells were extremely rare. Immunoelectron microscopy demonstrated that IC-IM formed close associations with neurons containing nitric oxide synthase-like immunoreactivity (NOS-LI) or vesicular acetylcholine transporter-like immunoreactivity (vAChT-LI), suggesting innervation by both inhibitory and excitatory motor neurons. IC-IM were also labeled with anti-NOS antibodies. These observations suggest that IC-IM are an integral part of the neuromuscular junction in the colon. These cells may be the primary site of innervation, and neural regulation of the musculature may occur via IC-IM.

Lung epithelial H292 cells induce differentiation of immature human HMC-1 mast cells by interleukin-6 and stem cell factor

BACKGROUND

Immature mast cells migrate into tissues where they differentiate into mature mast cells under the influence of local factors. In the airways of asthmatics increased numbers of chronically activated mast cells are located nearby the airway epithelium.

OBJECTIVE

The aim of this study was to evaluate whether and, if so, which products released by epithelial cells may affect mast cell proliferation and differentiation.

METHODS

We performed in vitro studies using the human lung mucoepidermoid carcinoma-derived H292 cell line and the immature human mast cell line, HMC-1. Proliferation was assessed by 3H-thymidine incorporation. Differentiation of HMC-1 cells was inferred from tryptase production.

RESULTS

Exposure of HMC-1 cells to medium conditioned for 48 h by H292 cells resulted in a reduction of proliferation with 65 +/- 4.9% (mean +/- SEM, n = 9) at day 5. Culturing HMC-1 cells for 8 days in the presence of H292-conditioned medium resulted in morphological changes indicative of differentiation, and in a 3.0 +/- 0.4-fold increase of tryptase production (P = 0.0039, n = 9). Conditioned medium from H292 cells that were stimulated by LPS also inhibited HMC-1 proliferation. Inhibitory antibodies against two mediators from H292 cells, interleukin-6 (IL-6) and stem cell factor (SCF), abolished the increase in HMC-1 tryptase production induced by H292-conditioned medium. Recombinant human (rh) IL-6, but not rhSCF, reduced HMC-1 proliferation with 44% and 13% at day 3 and 5, respectively. Surprisingly, rhIL-6 did not increase HMC-1 tryptase production significantly whereas incubation with rhSCF did (1.5 +/- 0.1-fold, P = 0.002, n = 10) although the increase was less than observed for conditioned medium.

CONCLUSION

Epithelial-derived IL-6 and SCF are implicated in differentiation of HMC-1 cells but additional factors are not excluded. As activated primary bronchial epithelial cells also express IL-6 and SCF, it should be considered that these cells are involved in mast cell differentiation within the airways, particularly in diseases where epithelial cells are activated, such as asthma.

Surface expression of HLA-DM on dendritic cells derived from CD34-positive bone marrow haematopoietic stem cells

HLA-DM has been known to be largely absent from the cell surface of antigen-presenting cells, accumulating instead in the intracellular compartment. In this study, we demonstrated that a population of HLA-DM-positive (HLA-DM+) dendritic cells (DCs) can be identified in an in vitro culture of CD34+ bone marrow haematopoietic stem cells. CD34+ bone marrow cells of healthy donors were used to generate DCs with the recombinant human cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), tumour necrosis factor alpha (TNF-alpha) and stem cell factor (SCF), both with and without interleukin 4 (IL-4). Flow cytometric analysis demonstrated that HLA-DM+ cells comprised 2.5 +/- 0.9% and 1.8 +/- 0.4% of the CD34+ cell-derived progeny in the presence of GM-CSF, TNF-alpha and SCF after 7 d and 14 d of culture respectively. The number of HLA-DM molecules expressed per HLA-DM+ cell on d 7 was significantly higher than that on d 14 (1410 +/- 47 versus 370 +/- 25, P < 0.05). The addition of IL-4 to the cytokines from the commencement of culture increased the proportion of HLA-DM+ cells and increased the number of HLA-DM molecules per HLA-DM+ cell significantly (P < 0.05). Although most of the HLA-DM+ cells expressed CD1a, CD80 or CD86 antigen, only a small proportion of CD1a+, CD80+ or CD86+ cells expressed HLA-DM. About half the HLA-DM+ cells expressed CD83. The addition of IL-4 resulted in a decrease in the expression of CD83 on the HLA-DM+ cells on d 7. Microscopic evaluations of sorted HLA-DM+ cells revealed the characteristic morphological features of DCs. Primary mixed lymphocyte cultures demonstrated that the HLA-DM+ cells elicited a vigorous proliferation of allogeneic T cells. The level of antigen-specific T-cell activation induced by antigen-pulsed, chloroquine-treated HLA-DM+ cells was substantially higher than that induced by HLA-DM- cells (P < 0.05). These results show that HLA-DM can be used as a useful DC lineage-specific marker, as well as a tool for the characterization of DCs and human immunotherapy.