Human cytomegalovirus downregulates complement receptors (CR3, CR4) and decreases phagocytosis by macrophages

Human cytomegalovirus (HCMV) infection is associated with an increased susceptibility to opportunistic infections. Although the subversion of adaptive immune responses has been extensively studied, the consequences of HCMV infection on natural immune responses are not well documented. A striking selective downmodulation of CD11b/CD18 (CR3) or CD11c/CD18 (CR4) was found upon HCMV infection, on two models, the monocytic THP-1 cell line and monocyte- derived macrophages. HCMV-infected macrophages have an altered adhesion/phagocytic capacity to Candida albicans, a pathogen responsible for some opportunistic infections in immunocompromised patients. These results suggest a new mechanism implicated in the augmentation of opportunistic infections in HCMV patients.

Anatomic localization of immature and mature dendritic cells in an ectopic lymphoid organ: correlation with selective chemokine expression in rheumatoid synovium

It remains to be clarified whether dendritic cells (DC) reach the rheumatoid arthritis (RA) synovium, considered an ectopic lymphoid organ, as mature cells or undergo local maturation. We characterized by immunohistochemistry the DC subsets and used tonsils as a control. Immature and mature DC were defined by CD1a and DC-lysosome-associated membrane protein/CD83 expression, respectively. Immature DC were mainly detected in the lining layer in RA synovium. Mature DC were exclusively detected in the lymphocytic infiltrates. The DC-lysosome-associated membrane protein/CD1a ratio was 1.1 in RA synovium and 5.3 in tonsils, suggesting the relative accumulation of immature DC in RA synovium. We then focused on the expression of CCL20/CCR6 and CCL19/CCR7, CCL21/CCR7 chemokine/receptor complex, which control immature and mature DC migration respectively. A close association was observed between CCL20-producing cells and CD1a(+) cells, suggesting the contribution of CCL20 to CCR6(+) cell homing. Conversely, CCL21 and CCL19 expression was only detected in perivascular infiltrates. The association among CCL19/21-producing cells, CCR7 expression, and mature DC accumulation is in line with the roles of these chemokines in mature CCR7(+) DC homing to lymphocytic infiltrates. The role of DC in disease initiation and perpetuation makes chemokines involved in DC migration a potential therapeutic target.

Increased generation of dendritic cells from myeloid progenitors in autoimmune-prone nonobese diabetic mice

Aberrant dendritic cell (DC) development and function may contribute to autoimmune disease susceptibility. To address this hypothesis at the level of myeloid lineage-derived DC we compared the development of DC from bone marrow progenitors in vitro and DC populations in vivo in autoimmune diabetes-prone nonobese diabetic (NOD) mice, recombinant congenic nonobese diabetes-resistant (NOR) mice, and unrelated BALB/c and C57BL/6 (BL/6) mice. In GM-CSF/IL-4-supplemented bone marrow cultures, DC developed in significantly greater numbers from NOD than from NOR, BALB/c, and BL/6 mice. Likewise, DC developed in greater numbers from sorted (lineage(-)IL-7Ralpha(-)SCA-1(-)c-kit(+)) NOD myeloid progenitors in either GM-CSF/IL-4 or GM-CSF/stem cell factor (SCF)/TNF-alpha. [(3)H]TdR incorporation indicated that the increased generation of NOD DC was due to higher levels of myeloid progenitor proliferation. Generation of DC with the early-acting hematopoietic growth factor, flt3 ligand, revealed that while the increased DC-generative capacity of myeloid-committed progenitors was restricted to NOD cells, early lineage-uncommitted progenitors from both NOD and NOR had increased DC-generative capacity relative to BALB/c and BL/6. Consistent with these findings, NOD and NOR mice had increased numbers of DC in blood and thymus and NOD had an increased proportion of the putative myeloid DC (CD11c(+)CD11b(+)) subset within spleen. These findings demonstrate that diabetes-prone NOD mice exhibit a myeloid lineage-specific increase in DC generative capacity relative to diabetes-resistant recombinant congenic NOR mice. We propose that an imbalance favoring development of DC from myeloid-committed progenitors predisposes to autoimmune disease in NOD mice.

Marked increase in number of dendritic cells in autoimmune-prone (NZW x BXSB)F1 mice with age

Here, we report that the number of CD11c(+)CD3(-) B220(-) cells increases in autoimmune-prone male (NZW x BXSB)F1 (W/BF1) mice with age. The CD11c(+)CD3(-)B220(-) cells from W/BF1 mice show a typical stellate shape and induce the proliferation of T cells. In the CD11c(+)CD3(-)B220(-) cells from W/BF1 mice, CD11b (Mac-1alpha), NK 1.1, and CD95 (Fas) are upregulated in comparison with normal mice, while the expression of CD8alpha, CD117 (c-kit), CD135 (Flk-2/Flt-3), and Sca-1 decreases. There is a significant increase in Flt-3L (FL) mRNA in the bone marrow of W/BF1 mice with age. Moreover, activated hemopoietic cells express high levels of FL. The injection of CD11c(+)CD3(-)B220(-) cells from old W/BF1 mice to young W/BF1 mice transiently induces autoimmune disease (thrombocytopenia). These results suggest that hyperproduction of FL from activated hemopoietic cells induces a dramatic increase in the number of dendritic cells in aged W/BF1 mice, followed by the acceleration of autoimmunity.

During differentiation of the monocytic cell line U937, Pur alpha mediates induction of the CD11c beta 2 integrin gene promoter

CD11c is a member of the beta(2) integrin family of adhesion molecules that, together with CD18, forms a heterodimeric receptor on the surface of myeloid, NK, dendritic, and certain leukemic, lymphoma, and activated lymphoid cells. Monocytic differentiation is associated with an induction of both CD11c and CD18 gene expression. The resulting CD11c/CD18 receptor mediates firm adhesion to the vascular endothelium, transendothelial migration, chemotaxis, and phagocytosis. Monocytic differentiation can be mimicked in vitro by treatment of the promonocytic cell line U937 with PMA. Recently, we reported that in U937 cells, expression of the CD11c gene is controlled by an unidentified transcription factor that binds ssDNA. This finding suggested that DNA secondary structure plays an important role in controlling the CD11c gene and prompted us to search for additional ssDNA-binding activities with which this gene interacts. In this study, we report that in U937 cells, expression of the CD11c gene is mediated by the ssDNA-binding protein Puralpha. During PMA-induced differentiation, the ability of Puralpha to activate the CD11c promoter in U937 cells increases, as does that of Sp1. Together, these increases in the functional activity of both Puralpha and Sp1 combine to induce CD11c expression.

Interferon-beta increases the stimulatory capacity of monocyte-derived dendritic cells to induce IL-13, IL-5 and IL-10 in autologous T-cells

Dendritic cells (DCs) are key regulators of immune responses and have been associated with autoimmunity in animal models and human disease. The effects of interferon beta (IFN-beta), an immunomodulatory cytokine used in multiple sclerosis (MS) therapy, on DCs are not well understood. Monocyte-derived DCs at different stages of maturation were stimulated with IFN-beta and DC-phenotype and stimulatory function were measured. IFN-beta inhibited the development of DCs at early stages but enhanced DC maturation. Moreover, IFN-beta enhanced the capacity of DCs to stimulate autologous T-cells to secrete IL-13, IL-10 and IL-5. Thus, IFN-beta has both immunostimulatory and immunosuppressive effects on DCs depending on the stage of maturation.

Expression of endothelial cell-associated molecules in AML cells

Recently, it has been clarified that interaction between hematopoietic cells and endothelial cells is important in normal hematopoiesis and leukemogenesis. In this study, we examined the relationship between AML cells and endothelial cells by analyzing the expression profile of angiogenic factors, angiopoietin-1 (Ang-1), Ang-2, Tie-2 (a receptor for angiopoietins) and vascular endothelial growth factor (VEGF). Our results demonstrated that CD7(+)AML expressed Ang-2 mRNA frequently and integrin-family adhesion molecules (CD11c and CD18) intensively, suggesting the close correlation with endothelial cells. On the other hand, in t(8;21) AML cells, expression of Ang-2 was infrequent and expression of integrin-family adhesion molecules (CD11b, CD11c and CD18) was weak, suggesting the sparse association with endothelial cells. As for CD7(+)AML cells, despite the frequent and intense expression of endothelial cell-associated molecules (such as Ang-2, CD11c and CD18), intensity of Tie-2 expression was quite low (P < 0.05). Ang-2 expressed in CD7(+)AML cells is not considered to act in an autocrine fashion, but to work on endothelial cells to "feed" leukemic cells. Although Ang-2 is recognized as a natural antagonist for Tie-2, our data presented here suggested the alternative role of Ang-2 in the relationship between endothelial cells and leukemia cells, at least in a subset of leukemia such as CD7(+)AML. These results were supported by the study using AML cell lines, KG-1 (CD7 negative) and its subline KG-1a (CD7 positive); KG-1 had mRNA expression profile of Ang-1(+)Ang-2(-)Tie-2(+), while KG-1a showed Ang-1(+)Ang-2(+)Tie-2(-). These difference in the expression profile of angiogenic factors between CD7(+)AML and t(8;21)AML may explain the characteristic morphological features of these leukemias (CD7(+)AML as blastic type and t(8;21)AML as differentiative type).

Mitogen-activated protein kinase is required for bryostatin 1-induced differentiation of the human acute lymphoblastic leukemia cell line Reh

Bryostatin 1 (bryo 1) is known to induce the differentiation and cell cycle arrest of human lymphoid leukemia cells in vitro. The extracellular signal-regulated kinase (ERK), originally identified as a participant in mitogenic signaling, has recently been implicated in the signaling of cellular differentiation. To examine the role of the ERK/mitogen-activated protein (MAP) kinase pathway in B-lymphoid cell differentiation of the Reh Acute Lymphoblastic Leukemia cell line, the effects of bryo 1 on ERK activation were determined. On bryo 1 treatment, the activity of ERK2 (p42) rapidly increased, with ERK1 (p44) protein levels remaining constant. p44/42 immunoprecipitates from lysates of bryo 1-treated cells had increased their ability to phosphorylate the transcription factor Elk-1. Constitutive AP-1 activity was shown to be potentiated after bryo 1 treatment using electrophoretic mobility shift assays. The protein composition of the AP-1 transcription factor complex activated by bryo 1 was analyzed using supershift analysis with specific antibodies against c-Fos, Fos B, c-Jun, Jun B, and Jun D proteins. Supershift analysis revealed that the bryo 1-induced AP-1 complex was composed predominantly of Fos B and Jun D. Therefore, we evaluated the effects of inhibiting MAP/ERK kinase (MEK) on both DNA binding and cellular differentiation. Treatment of Reh cells with 20 microM PD98059, a specific inhibitor of MEK, inhibited bryo 1-induced ERK activity and DNA binding. Furthermore, PD98059 blocked the bryo 1-induced differentiation of Reh cells, as assessed by a number of features associated with lymphoid differentiation, including changes in morphology, cell growth arrest, attachment, and increased expression of the leukocyte integrin CD11c. Moreover, transient transfection of Reh cells with antisense MAP kinase oligonucleotides blocked bryo 1-induced expression of CD11c. Our analysis also shows that CD11c's gene promoter activity is augmented by bryo 1. Therefore, we conclude that activation of the MEK/ERK signaling pathway is necessary for bryo 1-induced differentiation of the pre-B Acute Lymphoblastic Leukemia cell line Reh.

Monocyte differentiation to macrophage requires interferon regulatory factor 7

Interferon regulatory factors are a growing family of transcription factor that have been implicated in cellular events such as cell-growth regulation, antiviral defense, and development of the immune system. Interferon regulatory factor 7 (IRF-7) is expressed predominantly in lymphoid tissues and has been studied extensively in the context of viral infection and the induction of interferon and cytokine gene expression. In this paper, the involvement of IRF-7 in monocyte differentiation was examined in U937, HL60, and human primary macrophages. We report the induction of IRF-7 expression by 12-O-tetradecanoylphorbol-13-acetate in U937 and HL60 cells and demonstrate that this induction is essential for the monocyte differentiation to macrophages. We show that the monocyte differentiation is inhibited in cells expressing a dominant negative IRF-7 mutant, as evidenced by decreased expression of two macrophage-differentiation markers, CD11b and CD11c, and impaired phagocytic activity. In addition, we demonstrate that overexpression of IRF-7 is sufficient to trigger monocyte differentiation and to induce cell cycle arrest. The identification of IRF-7 as a key regulator in monocyte differentiation suggests a novel function of IRF-7 in innate immunity.

CD11c(+)B220(+)Gr-1(+) cells in mouse lymph nodes and spleen display characteristics of plasmacytoid dendritic cells

Human plasmacytoid dendritic cells (pDCs) are major producers of IFNalpha, are activated by CpG motifs, and are believed to enter lymph nodes (LNs) via L-selectin dependent extravasation across high endothelial venules. To identify a similar murine DC type, CD11c(+) cells in the LNs of L-selectin-deficient and control BALB/c mice were compared, revealing a population of CD11c(+)CD11b(-) cells that is reduced 85% in the LNs of L-selectin-deficient mice. These cells are Gr-1(+)B220(+)CD19(-), either CD4(+) or CD8(+), and localize within T cell zones of LNs. Freshly isolated CD11c(+)Gr-1(+) cells express major histocompatibility complex class II at low levels, display a plasmacytoid morphology, and survive poorly in culture. Their survival is increased and they develop a DC-like morphology in interleukin 3 and CpG. Like human pDCs, CD11c(+)Gr-1(+) cells stimulate T cell proliferation after activation with CpG and produce IFNalpha after stimulation with influenza virus. These cells also display a strain-specific variation in frequency, being fivefold increased in the LNs of BALB/c relative to C57BL/6 mice. These CD11c(+)CD11b(-)B220(+)Gr-1(+) cells appear to be the murine equivalent of human pDCs.

Differential involvement of dendritic cell subsets during acute Salmonella infection

Within murine CD11c(+) dendritic cells (DC), CD8alpha+, CD8alpha-CD4+, and CD8alpha-CD4- subsets are defined. This study characterized the localization, number, and function of these subsets during acute Salmonella typhimurium infection. Immunohistochemical and flow cytometric analyses of spleens from mice orally infected with virulent S. typhimurium revealed that in situ redistribution and alteration in the absolute number and function of DC occurred in a subset-specific manner during infection. CD8alpha-CD4+ DC present at B cell follicle borders in the spleen of naive mice were absent 5 days post-Salmonella infection, despite no overall change in the absolute number of CD8alpha-CD4+ splenic DC. CD8alpha+ and CD8alpha-CD4- DC were prominently associated with the red pulp, and the frequency of these cells increased strikingly 5 days post-Salmonella infection. Significant quantitative increases in both CD8alpha+ and CD8alpha-CD4- subsets were associated with the in situ redistribution. Examination of Salmonella-infected TAP1(-/-)/beta(2)-microglobulin(-/-) mice, which lack CD8alpha+ T cells, confirmed the differential subset-specific modulations in the DC populations both in situ and quantitatively. Ex vivo intracellular cytokine analysis showed significantly increased frequencies of CD8alpha(+) DC producing TNF-alpha at days 2 and 5 postinfection. In contrast, CD4+ DC producing TNF-alpha were transiently increased followed by a significant reduction. No significant increase in IL-12p40 or IL-10 production by splenic DC was detected during the first 5 days post-S. typhimurium infection. Together these data reveal differential modulation of splenic DC subsets with regard to organization, number, and cytokine production during the course of acute Salmonella infection.

Increased histidine decarboxylase expression during in vitro monocyte maturation; a possible role of endogenously synthesised histamine in monocyte/macrophage differentiation

OBJECTIVE

In this study the expression of histidine decarboxylase (HDC), the pivotal enzyme in histamine formation and the effect of endogenously produced histamine on differentiation antigens was examined during in vitro differentiation of human monocytes.

MATERIAL AND TREATMENT

Human elutriated monocytes from healthy volunteers were incubated with macrophage colony stimulating factor (M-CSF) and the expression of HDC was followed at both mRNA and protein levels. To study the possible function of histamine we followed the expression of some cell surface markers (CD14, CD16, CD91, CD49d and CD11c) relevant for phagocytic differentiation upon incubation in the presence of different histamine inhibitors, an HDC inhibitor: S(+)-alpha-fluoromethyl-histidine HCl, (alphaFMH), a compound that disturbs the interaction of histamine with intracellular cyp450 moieties: N,N-diethyl-2-[4-(phenylmethyl) phenoxy]-ethanamine HCI, (DPPE); and H1 and H2 receptor antagonists, Triprolidine and Cimetidine.

RESULTS

During in vitro culture of elutriated human monocytes, in the presence of M-CSF, the gene expression and biosynthesis of HDC was considerably increased. The various antihistamine agents decreased the expression of the cell surface markers examined in this study.

CONCLUSIONS

These data support the elevation of HDC expression during human monocytic differentiation and the possibility that monocyte-derived histamine is partially involved in regulation of M-CSF induced in vitro human monocyte/macrophage phagocytic differentiation.

Human thymic stromal lymphopoietin preferentially stimulates myeloid cells

The sequence of a novel hemopoietic cytokine was discovered in a computational screen of genomic databases, and its homology to mouse thymic stromal lymphopoietin (TSLP) suggests that it is the human orthologue. Human TSLP is proposed to signal through a heterodimeric receptor complex that consists of a new member of the hemopoietin family termed human TSLP receptor and the IL-7R alpha-chain. Cells transfected with both receptor subunits proliferated in response to purified, recombinant human TSLP, with induced phosphorylation of Stat3 and Stat5. Human TSLPR and IL-7Ralpha are principally coexpressed on monocytes and dendritic cell populations and to a much lesser extent on various lymphoid cells. In accord, we find that human TSLP functions mainly on myeloid cells; it induces the release of T cell-attracting chemokines from monocytes and, in particular, enhances the maturation of CD11c(+) dendritic cells, as evidenced by the strong induction of the costimulatory molecules CD40 and CD80 and the enhanced capacity to elicit proliferation of naive T cells.

Complement components, but not complement inhibitors, are upregulated in atherosclerotic plaques

Complement activation occurs in atherosclerotic plaques. The capacity of arterial tissue to inhibit this activation through generation of the complement regulators C1 inhibitor, decay accelerating factor, membrane cofactor protein (CD46), C4 binding protein (C4BP), and protectin (CD59) was evaluated in pairs of aortic atherosclerotic plaques and nearby normal artery from 11 human postmortem specimens. All 22 samples produced mRNAs for each of these proteins. The ratios of plaque versus normal artery pairs was not significantly different from unity for any of these inhibitors. However, in plaques, the mRNAs for C1r and C1s, the substrates for the C1 inhibitor, were increased 2.35- and 4.96-fold, respectively, compared with normal artery; mRNA for C4, the target for C4BP, was elevated l.34-fold; and mRNAs for C7 and C8, the targets for CD59, were elevated 2.61- and 3.25-fold, respectively. By Western blotting and immunohistochemistry, fraction Bb of factor B, a marker of alternative pathway activation, was barely detectable in plaque and normal arterial tissue. These data indicate that it is primarily the classical, not the alternative pathway, that is activated in plaques and that key inhibitors are not upregulated to defend against this activation.

Aspirin inhibits in vitro maturation and in vivo immunostimulatory function of murine myeloid dendritic cells

Aspirin is the most commonly used analgesic and antiinflammatory agent. In this study, at physiological concentrations, it profoundly inhibited CD40, CD80, CD86, and MHC class II expression on murine, GM-CSF + IL-4 stimulated, bone marrow-derived myeloid dendritic cells (DC). CD11c and MHC class I expression were unaffected. The inhibitory action was dose dependent and was evident at concentrations higher than those necessary to inhibit PG synthesis. Experiments with indomethacin revealed that the effects of aspirin on DC maturation were cyclooxygenase independent. Nuclear extracts of purified, aspirin-treated DC revealed a decreased NF-kappaB DNA-binding activity, whereas Ab supershift analysis indicated that aspirin targeted primarily NF-kappaB p50. Unexpectedly, aspirin promoted the generation of CD11c+ DC, due to apparent suppression of granulocyte development. The morphological and ultrastructural appearance of aspirin-treated cells was consistent with immaturity. Aspirin-treated DC were highly efficient at Ag capture, via both mannose receptor-mediated endocytosis and macropinocytosis. By contrast, they were poor stimulators of naive allogeneic T cell proliferation and induced lower levels of IL-2 in responding T cells. They also exhibited impaired IL-12 expression and did not produce IL-10 after LPS stimulation. Assessment of the in vivo function of aspirin-treated DC, pulsed with the hapten trinitrobenzenesulfonic acid, revealed an inability to induce normal cell-mediated contact hypersensitivity, despite the ability of the cells to migrate to T cell areas of draining lymphoid tissue. These data provide new insight into the immunopharmacology of aspirin and suggest a novel approach to the manipulation of DC for therapeutic application.

IL-12 suppression during experimental endotoxin tolerance: dendritic cell loss and macrophage hyporesponsiveness

Endotoxin tolerance, the transient, secondary down-regulation of a subset of endotoxin-driven responses after exposure to bacterial products, is thought to be an adaptive response providing protection from pathological hyperactivation of the innate immune system during bacterial infection. However, although protecting from the development of sepsis, endotoxin tolerance also can lead to fatal blunting of immunological responses to subsequent infections in survivors of septic shock. Despite considerable experimental effort aimed at characterizing the molecular mechanisms responsible for a variety of endotoxin tolerance-related phenomena, no consensus has been achieved yet. IL-12 is a macrophage- and dendritic cell (DC)-derived cytokine that plays a key role in pathological responses to endotoxin as well as in the induction of protective responses to pathogens. It recently has been shown that IL-12 production is suppressed in endotoxin tolerance, providing a likely partial mechanism for the increased risk of secondary infections in sepsis survivors. We examined the development of IL-12 suppression during endotoxin tolerance in mice. Decreased IL-12 production in vivo is clearly multifactorial, involving both loss of CD11c(high) DCs as well as alterations in the responsiveness of macrophages and remaining splenic DCs. We find no demonstrable mechanistic role for B or T lymphocytes, the soluble mediators IL-10, TNF-alpha, IFN-alphabeta, or nitric oxide, or the NF-kappaB family members p50, p52, or RelB.

Bacterial CpG-DNA triggers activation and maturation of human CD11c-, CD123+ dendritic cells

Human plasmacytoid precursor dendritic cells (ppDC) are a major source of type I IFN upon exposure to virus and bacteria, yet the stimulus causing their maturation into DCs is unknown. After PBMC activation with immunostimulatory bacterial DNA sequences (CpG-DNA) we found that ppDC are the primary source of IFN-alpha. In fact, either CpG-DNA or dsRNA (poly(I:C)) induced IFN-alpha from purified ppDC. Surprisingly, only CpG-DNA triggered purified ppDC survival, maturation, and production of TNF, GM-CSF, IL-6, and IL-8, but not IL-10 or IL-12. Known DC activators such as CD40 ligation triggered ppDC maturation, but only IL-8 production, while bacterial LPS was negative for all activation criteria. An additional finding was that only CpG-DNA could counteract IL-4-induced apoptosis in ppDC. Therefore, CpG-DNA represents a pathogen-associated molecular pattern for ppDC. In contrast to these finding, CpG-DNA, like LPS, caused TNF, IL-6, and IL-12 release from PBMC and purified monocytes; however, differentiation of monocytes into DCs with GM-CSF and IL-4 unexpectedly resulted in refractoriness to CpG-DNA, but not LPS. Taken together, these results suggest that within a DC subset a multiplicity of responses can be generated by distinct environmental stimuli and that responses to a given stimulus may be dissimilar between DC subsets.

Endothelial cell activation by myeloblasts: molecular mechanisms of leukostasis and leukemic cell dissemination

Leukostasis and tissue infiltration by leukemic cells are poorly understood life-threatening complications of acute leukemia. This study has tested the hypothesis that adhesion receptors and cytokines secreted by blast cells play central roles in these reactions. Immunophenotypic studies showed that acute myeloid leukemia (AML) cells (n = 78) of the M0 to M5 subtypes of the French-American-British Cooperative Group expressed various amounts of adhesion receptors, including CD11a, b, c/CD18, CD49d, e, f/CD29, CD54, sCD15, and L-selectin. The presence of functional adhesion receptors was evaluated using a nonstatic adhesion assay. The number of blast cells attached to unactivated endothelium increased by 7 to 31 times after a 6-hour exposure of endothelium to tumor necrosis factor (TNF)-alpha. Inhibition studies showed that multiple adhesion receptors--including L-selectin, E-selectin, VCAM-1, and CD11/CD18--were involved in blast cell adhesion to TNF-alpha-activated endothelium. Leukemic cells were then cocultured at 37 degrees C on unactivated endothelial cell monolayers for time periods up to 24 hours. A time-dependent increase in the number of blasts attached to the endothelium and a concomitant induction of ICAM-1, VCAM-1, and E-selectin were observed. Additional experiments revealed that endothelial cell activation by leukemic myeloblasts was caused by cytokine secretion by blast cells, in particular TNF-alpha and IL-1 beta, and direct contacts between adhesion receptors expressed by blast cells and endothelial cells. Thus, leukemic cells have the ability to generate conditions that promote their own adhesion to vascular endothelium, a property that may have important implications for the pathophysiology of leukostasis and tissue infiltration by leukemic blast cells. (Blood. 2001;97:2121-2129)

Brain dendritic cells and macrophages/microglia in central nervous system inflammation

Microglia subpopulations were studied in mouse experimental autoimmune encephalomyelitis and toxoplasmic encephalitis. CNS inflammation was associated with the proliferation of CD11b(+) brain cells that exhibited the dendritic cell (DC) marker CD11c. These cells constituted up to 30% of the total CD11b(+) brain cell population. In both diseases CD11c(+) brain cells displayed the surface phenotype of myeloid DC and resided at perivascular and intraparenchymatic inflammatory sites. By lacking prominent phagocytic organelles, CD11c(+) cells from inflamed brain proved distinct from other microglia, but strikingly resembled bone marrow-derived DC and thus were identified as DC. This brain DC population comprised cells strongly secreting IL-12p70, whereas coisolated CD11c(-) microglia/brain macrophages predominantly produced TNF-alpha, GM-CSF, and NO. In comparison, the DC were more potent stimulators of naive or allogeneic T cell proliferation. Both DC and CD11c(-) microglia/macrophages from inflamed brain primed naive T cells from DO11.10 TCR transgenic mice for production of Th1 cytokines IFN-gamma and IL-2. Resting microglia that had been purified from normal adult brain generated immature DC upon exposure to GM-CSF, while CD40 ligation triggered terminal maturation. Consistently, a functional maturation of brain DC was observed to occur following the onset of encephalitis. In conclusion, these findings indicate that in addition to inflammatory macrophage-like brain cells, intraparenchymatical DC exist in autoimmune and infectious encephalitis. These DC functionally mature upon disease onset and can differentiate from resident microglia. Their emergence, maturation, and prolonged activity within the brain might contribute to the chronicity of intracerebral Th1 responses.

Distinct CpG DNA and polyinosinic-polycytidylic acid double-stranded RNA, respectively, stimulate CD11c- type 2 dendritic cell precursors and CD11c+ dendritic cells to produce type I IFN

Two classes of nucleic acids, bacterial DNA containing unmethylated CpG motifs and dsRNA in viruses, induce the production of type I IFN that contributes to the immunostimulatory effects of these microbial molecules. Thus, it is important to determine which cells produce type I IFN in response to CpG DNA and dsRNA. CD4(+)CD11c(-) type 2 dendritic cell precursors (pre-DC2) were identified as the main producers of type I IFN in human blood in response to viruses. Here we asked whether pre-DC2 also produce type I IFN in response to CpG DNA and dsRNA. Oligodeoxynucleotides containing particular palindromic CpG motifs induced pre-DC2, but not CD11c(+) blood DC or monocytes, to produce IFN-alpha. In contrast, a synthetic dsRNA, polyinosinic polycytidylic-acid, induced CD11c(+) DC, but not pre-DC2 or monocytes, to produce IFN-alphabeta. These data indicate that CpG DNA and polyinosinic-polycytidylic acid stimulate different types of cells to produce type I IFN and that it is important to select oligodeoxynucleotides containing particular CpG motifs to induce pre-DC2 to produce type I IFN, which may play a key role in the strong adjuvant effects of CpG DNA.

Dendritic cells are sufficient to cross-present self-antigens to CD8 T cells in vivo

The mechanism of cross-presentation enables professional APCs to induce CD8 T cell-mediated immune responses against exogenous Ags. Through this mechanism, APCs can induce either immunity against infectious pathogens or tolerance against self-Ag residing in extralymphatic locations. An unanswered question in this field concerns the identity of the cross-presenting APC. All major classes of professional APCs, particularly dendritic cells, macrophages, and B cells, have previously been shown to be able to cross-present Ags in vitro. In the present study, we have created transgenic mice where MHC class I expression is driven selectively in dendritic cells and provide direct in vivo evidence that dendritic cells are sufficient to cross-present exogenous self-Ags and induce Ag-specific cell division of CD8-positive T cells.

The potent adjuvant activity of archaeosomes correlates to the recruitment and activation of macrophages and dendritic cells in vivo

The unique glycerolipids of Archaea can be formulated into vesicles (archaeosomes) with potent adjuvant activity. We studied the effect of archaeosomes on APCs to elucidate the mechanism(s) of adjuvant action. Exposure of J774A.1 macrophages to archaeosomes in vitro resulted in up-regulation of B7.1, B7.2, and MHC class II molecules to an extent comparable to that achieved with LPS. Similarly, incubation of bone marrow-derived DCs with archaeosomes resulted in enhanced expression of MHC class II and B7.2 molecules. In contrast, conventional liposomes made from ester phospholipids failed to modulate the expression of these activation markers. APCs treated with archaeosomes exhibited increased TNF production and functional ability to stimulate allogenic T cell proliferation. More interestingly, archaeosomes enhanced APC recruitment and activation in vivo. Intraperitoneal injection of archaeosomes into mice led to recruitment of Mac1alpha(+), F4/80(+) and CD11c(+) cells. The expression of MHC class II on the surface of peritoneal cells was also enhanced. Furthermore, peritoneal cells from archaeosome-injected mice strongly enhanced allo-T cell proliferation and cytokine production. The ability of archaeosome-treated APCs to stimulate T cells was restricted to Mac1alpha(high), B220(-) cells in the peritoneum. These Mac1alpha(high) cells in the presence of GM-CSF gave rise to both F4/80(+) (macrophage) and CD11c(+) (dendritic) populations. Overall, the activation of APCs correlated to the ability of archaeosomes to induce strong humoral, T helper, and CTL responses to entrapped Ag. Thus, the recruitment and activation of professional APCs by archaeosomes constitutes an efficient self-adjuvanting process for induction of Ag-specific responses to encapsulated Ags.

Propofol depressed neutrophil hydrogen peroxide production more than midazolam, whereas adhesion molecule expression was minimally affected by both anesthetics in rats with abdominal sepsis

The treatment of sepsis may require mechanical ventilation of the lungs and sedation. Because neutrophils are the most important effector cells for protecting against sepsis, and propofol and midazolam are the most widely used anesthetics for sedation, we studied the effects of these two anesthetics on the neutrophil function during sepsis. Sepsis was induced in rats by cecal ligation and puncture. At either 4 h or 24 h after cecal ligation and puncture, blood and peritoneal neutrophils were obtained, incubated with the test anesthetics, and the hydrogen peroxide (H(2)O(2)) production and CD11b/c expression were determined by flow cytometry. In both early (at 4 h) and late (at 24 h) sepsis, propofol and midazolam depressed H(2)O(2) production by blood and peritoneal neutrophils at clinical concentrations. Propofol caused more depression than midazolam (P < 0.005). In both early and late sepsis, the effect of the anesthetics on the up-regulation of the stimulation-induced CD11b/c expression on blood neutrophils was minimal at clinical concentrations. If these results ultimately become clinically relevant, midazolam may be preferable to propofol for sedation during sepsis.

Haemodialysis monocytopenia: differential sequestration kinetics of CD14+CD16+ and CD14++ blood monocyte subsets

In peripheral blood the majority of circulating monocytes present a CD14highCD16- (CD14++) phenotype, while a subpopulation shows a CD14lowCD16+ (CD14+CD16+) surface expression. During haemodialysis (HD) using cellulosic membranes transient leukopenia occurs. In contrast, synthetic biocompatible membranes do not induce this effect. We compared the sequestration kinetics for the CD14+CD16+ and CD14++ monocyte subsets during haemodialysis using biocompatible dialysers. Significant monocytopenia, as measured by the leucocyte count, occurred only during the first 30 min. However, remarkable differences were observed between the different monocyte subsets. CD14++ monocyte numbers dropped to 77 +/- 13% of the predialysis level after 15 min, increasing to > or = 93% after 60 min. In contrast, the CD14+CD16+ subset decreased to 33 +/- 15% at 30 min and remained suppressed for the course of dialysis (67 +/- 11% at 240 min). Approximately 6 h after the end of HD the CD14+CD16+ cells returned to basal levels. Interestingly, the CD14+CD16+ monocytes did not show rebound monocytosis while a slight monocytosis of CD14++ monocytes was occasionally observed during HD. A decline in CD11c surface density paralleled the sequestration of CD14+CD16+ monocytes. Basal surface densities of important adhesion receptors differed significantly between the CD14+CD16+ and CD14++ subsets. In conclusion, during HD the CD14+CD16+ subset revealed different sequestration kinetics, with a more pronounced and longer disappearance from the blood circulation, compared with CD14++ monocytes. This sequestration kinetics may be due to a distinct surface expression of major adhesion receptors which facilitate leucocyte-leucocyte, as well as leucocyte-endothelial, interactions.

Inflammatory activation of neutrophils by Helicobacter pylori; a mechanism insensitive to pertussis toxin

Chronic active gastritis of the antral mucosa is a characteristic feature of infection with Helicobacter pylori and interactions between bacterial components and inflammatory cells are believed to play an important pathogenic role. Neutrophils stimulated with H. pylori sonicate were demonstrated to release L-selectin (CD62L) expressed on the cellular surface, with a subsequent up-regulation of the beta2-integrins CD11b and CD11c, both in a dose- and time-dependent manner, reaching maximum levels after 45-60 min of stimulation. No changes were observed for the CD11a receptor upon stimulation. The activating properties of H. pylori sonicates on neutrophils were heat-labile and susceptible to protease attack, indicating the protein nature of the activating factor. After size fractionation, the major neutrophil-inducing activity was detected in the high molecular weight fraction exhibiting urease activity. Pertussis toxin was unable to inhibit neutrophil activation by the H. pylori protein(s). We conclude that proteins from H. pylori have a potent inflammatory effect on the surface membrane molecules CD62L, CD11b and CD11c essential for transendothelial migration of neutrophils to areas of inflammation. The neutrophil-activating protein(s) act via a pertussis toxin-insensitive mechanism.

Cutting edge: heat shock protein gp96 induces maturation and migration of CD11c+ cells in vivo

Immunization of mice with the heat shock protein (HSP) gp96 but not control proteins leads to 5- to 7-fold enlargement of draining lymph nodes (LNs) resulting from accumulation of large numbers of mature CD11c(+) cells, but not T or B lymphocytes in them. The increase in size and cellularity is time-dependent; the draining LNs reach their peak size between 12 and 24 h after injection and regress to their normal size between 48 and 72 h after injection. The increment is elicited specifically in the draining LN but not in other LNs. This observation uncovers a novel aspect of HSP-APC interaction and adds to the mechanistic explanation for the unusually high immunogenicity of HSP-peptide complexes.

Plasmid vaccine expressing granulocyte-macrophage colony-stimulating factor attracts infiltrates including immature dendritic cells into injected muscles

Plasmid-encoded GM-CSF (pGM-CSF) is an adjuvant for genetic vaccines; however, little is known about how pGM-CSF enhances immunogenicity. We now report that pGM-CSF injected into mouse muscle leads to a local infiltration of potential APCs. Infiltrates reached maximal size on days 3 to 5 after injection and appeared in several large discrete clusters within the muscle. Immunohistological studies in muscle sections from mice injected with pGM-CSF showed staining of cells with the macrophage markers CD11b, Mac-3, IA(d)/E(d) and to the granulocyte marker GR-1 from day 1 through day 14. Cells staining with the dendritic cell marker CD11c were detected only on days 3 to 5. Muscles injected with control plasmids did not stain for CD11c but did stain for CD11b, Mac-3, IA(d)/E(d), and GR-1. No staining was observed with the APC activation markers, B7.1 or CD40, or with markers for T or B cells. These findings are consistent with the infiltrating cells in the pGM-CSF-injected muscles being a mixture of neutrophils, macrophages, and immature dendritic cells and suggest that the i.m. APCs may be enhancing immune responses to coinjected plasmid Ags. This hypothesis is supported by data showing that 1) separation of injections with pGM-CSF and Ag-expressing plasmid into different sites did not enhance immune responses and 2) immune enhancement was associated with the presence of CD11c+ cells in the infiltrates. Thus, pGM-CSF enhancement may depend on APC recruitment to the i.m. site of injection.

Lipopolysaccharide-dependent induction of leech leukocytes that cross-react with vertebrate cellular differentiation markers

We have designed experiments to characterise leech leukocytes that mediate inflammatory responses. Shortly after inflicting injury to the body wall in the presence of lipopolysaccharides, many cells resembling macrophages, NK cells and granulocytes of vertebrates and many invertebrates migrated to the lesioned area. Nuclei of migrating cells incorporated bromodeoxyuridine. Using human monoclonal antibodies, macrophage-like cells were positive for CD25, CD14, CD61, CD68, CD11b and CD11c. NK-like cells were positive for CD25, CD56, CD57 and CD16, and granulocytes were positive for CD11b and CD11c. In blots of leech extracts, the CD25 monoclonal antibody recognised a band of about 55 kD; the CD56 monoclonal antibody, two bands of about 140 and 210 kD; the CD57 monoclonal antibody, two bands of about 106 and 70 kD; the CD14 monoclonal antibody, a band of about 50 kD; the CD16 monoclonal antibody, a band of about 60 kD. CD61 and CD68 both recognised a band of about 110 kD; CD11b recognised a band of 200 kD, and CD11c, a band of 180 kD.

CD11c+ eosinophils in the murine thymus: developmental regulation and recruitment upon MHC class I-restricted thymocyte deletion

Eosinophils are bone marrow-derived cells released into the circulation during hypersensitivity reactions and parasitic infections. Under normal conditions most eosinophils are tissue bound, where their physiologic role is unclear. During in situ analysis of the thymic microenvironment for CD11c+ dendritic cell subpopulations (APC critical in the process of thymic negative selection) a discrete population of CD11b/CD11c double-positive cells concentrated in the cortico-medullary region of young mice was detected. Thymic CD11c+ cells were isolated, and the CD11b+ subpopulation (CD44high, class IIlow, CD11cint) was identified as mature eosinophils based on: scatter characteristics, major basic protein mRNA expression, and eosinophilic granules. They are hypodense, release high levels of superoxide anion, and express CD25, CD69, and mRNA for IL-4 and IL-13, but not GM-CSF or IL-5, suggesting a distinct state of activation. Thymic eosinophils are preferentially recruited during the neonatal period; absolute numbers increased 10-fold between 7-14 days to reach parity with dendritic cells before diminishing. In a model of acute negative selection, eosinophil numbers were increased 2-fold 6 h after cognate peptide injection into MHC class I-restricted female H-Y TCR transgenic mice. In both peptide-treated female and negatively selecting male H-Y TCR mice, clusters of apoptotic bodies were associated with eosinophils throughout the thymus. Our data demonstrate a temporal and spatial association between eosinophil recruitment and class I-restricted selection in the thymus, suggesting an immunomodulatory role for eosinophils under nonpathological conditions.

Suppression of cytokine production and cell adhesion molecule expression in human monocytic cell line THP-1 by Tripterygium wilfordii polysaccharide moiety

Extracts of the vine-like plant Tripterygium wilfordii (TW) have been widely used in China as an immunosuppressant and anti-inflammatory drug for the treatments of rheumatoid arthritis, lupus erythematosus and other inflammatory disorders. In this study the molecular mechanisms of action of three TW extracts (ethanol, aqueous, polysaccharide) on the expression of inflammatory cytokines and adhesion molecules were investigated by RT-PCR and immunofluorescence binding techniques. The lipopolysaccharide (LPS)-mediated stimulatory effects of tumor necrosis factor-alpha (TNF-alpha) cytokine production and cell adhesion molecule (CD11c, CD18, CD14, CD54) expression in human monocytic THP-1 cells were modulated by treatments of the TW extracts or tacrolimus (FK506). The TW polysaccharide moiety exhibited more profound immunosuppressive properties than the aqueous and ethanol extracts. Biochemical characterization of the polysaccharide moiety revealed a major molecular weight of 22 kDa (viz. PSP22). The PSP22 was found to be a potential immunosuppressant that manifests the necessary immunomodulating properties.

Comparative studies of the colonic in situ expression of intercellular adhesion molecules (ICAM-1, -2, and -3), beta2 integrins (LFA-1, Mac-1, and p150,95), and PECAM-1 in ulcerative colitis and Crohn's disease

A dysregulated local immune defense with a constant influx of leukocytes provides a basis for continuous intestinal inflammation in ulcerative colitis (UC) and Crohn's disease (CD). Cell adhesion molecules are pivotal for the migration of leukocytes from the circulation toward the colonic epithelium. A study quantifying the cells expressing intercellular adhesion molecules (ICAMs), beta2 integrins, and platelet-endothelial cell adhesion molecule-1 (PECAM-1) in the colon was performed to illustrate the leukocyte migration pathway in inflammatory bowel disease. Serial colonic sections (10 UC, 10 CD, and 10 controls) were stained immunohistochemically for ICAM-1, ICAM-2, ICAM-3, CD11a, CD11b, CD18, and PECAM-1. Cell adhesion molecule expression was evaluated quantitatively with reference to topographic localization. In UC, polymorphonuclear leukocytes (PMNs) in contact with the crypt epithelium and in crypt abscesses expressed CD11b. CD tissue was characterized by CD11a-, CD11c-, and ICAM-1-expressing cells. ICAM-1 was detected on endothelial cells, leukocytes, and apical parts of epithelial membranes, whereas ICAM-2 was expressed on basal epithelial membranes. Most infiltrating leukocytes expressed ICAM-3, whereas perivascular mononuclear cells expressed PECAM-1. Interestingly, the epithelial basement membrane in UC stained for CD18. In conclusion, CD11b, CD18, and ICAM-2 seem to be important for PMN transepithelial migration in UC, whereas CD11a, CD11c, ICAM-1, and ICAM-3 seem central in leukocyte locomotion and aggregation in CD. Differentiated upregulation of cell adhesion molecules is suggested to be essential for the diversities between UC and CD.

FDF03, a novel inhibitory receptor of the immunoglobulin superfamily, is expressed by human dendritic and myeloid cells

In this study, we describe human FDF03, a novel member of the Ig superfamily expressed as a monomeric 44-kDa transmembrane glycoprotein and containing a single extracellular V-set Ig-like domain. Two potential secreted isoforms were also identified. The gene encoding FDF03 mapped to chromosome 7q22. FDF03 was mostly detected in hemopoietic tissues and was expressed by monocytes, macrophages, and granulocytes, but not by lymphocytes (B, T, and NK cells), indicating an expression restricted to cells of the myelomonocytic lineage. FDF03 was also strongly expressed by monocyte-derived dendritic cells (DC) and preferentially by CD14+/CD1a- DC derived from CD34+ progenitors. Moreover, flow cytometric analysis showed FDF03 expression by CD11c+ blood and tonsil DC, but not by CD11c- DC precursors. The FDF03 cytoplasmic tail contained two immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences. When overexpressed in pervanadate-treated U937 cells, FDF03 was tyrosine-phosphorylated and recruited Src homology-2 (SH2) domain-containing protein tyrosine phosphatase (SHP)-2 and to a lesser extent SHP-1. Like engagement of the ITIM-bearing receptor LAIR-1/p40, cross-linking of FDF03 inhibited calcium mobilization in response to CD32/FcgammaRII aggregation in transfected U937 cells, thus demonstrating that FDF03 can function as an inhibitory receptor. However, in contrast to LAIR-1/p40, cross-linking of FDF03 did not inhibit GM-CSF-induced monocyte differentiation into DC. Thus, FDF03 is a novel ITIM-bearing receptor selectively expressed by cells of myeloid origin, including DC, that may regulate functions other than that of the broadly distributed LAIR-1/p40 molecule.

Polyethylene glycol-modified GM-CSF expands CD11b(high)CD11c(high) but notCD11b(low)CD11c(high) murine dendritic cells in vivo: a comparative analysis with Flt3 ligand

Dendritic cells (DC) are potent APCs that can be characterized in the murine spleen as CD11b(high)CD11c(high) or CD11b(low)CD11c(high). Daily injection of mice of Flt3 ligand (FL) into mice transiently expands both subsets of DC in vivo, but the effect of administration of GM-CSF on the expansion of DC in vivo is not well defined. To gain further insight into the role of GM-CSF in DC development and function in vivo, we treated mice with polyethylene glycol-modified GM-CSF (pGM-CSF) which has an increased half-life in vivo. Administration of pGM-CSF to mice for 5 days led to a 5- to 10-fold expansion of CD11b(high)CD11c(high) but not CD11b(low)CD11c(high) DC. DC from pGM-CSF-treated mice captured and processed Ag more efficiently than DC from FL-treated mice. Although both FL- and pGM-CSF-generated CD11b(high)CD11c(high) DC were CD8alpha-, a greater proportion of these DC from pGM-CSF-treated mice were 33D1+ than from FL-treated mice. CD11b(low)CD11c(high) DC from FL-treated mice expressed high levels of intracellular MHC class II. DC from both pGM-CSF- and FL-treated mice expressed high levels of surface class II, low levels of the costimulatory molecules CD40, CD80, and CD86 and were equally efficient at stimulating allogeneic and Ag-specific T cell proliferation in vitro. The data demonstrate that treatment with pGM-CSF in vivo preferentially expands CD11b(high)CD11c(high) DC that share phenotypic and functional characteristics with FL-generated CD11b(high)CD11c(high) DC but can be distinguished from FL-generated DC on the basis of Ag capture and surface expression of 33D1.

Flt3-ligand and granulocyte colony-stimulating factor mobilize distinct human dendritic cell subsets in vivo

Dendritic cells (DCs) have a unique ability to stimulate naive T cells. Recent evidence suggests that distinct DC subsets direct different classes of immune responses in vitro and in vivo. In humans, the monocyte-derived CD11c+ DCs induce T cells to produce Th1 cytokines in vitro, whereas the CD11c- plasmacytoid T cell-derived DCs elicit the production of Th2 cytokines. In this paper we report that administration of either Flt3-ligand (FL) or G-CSF to healthy human volunteers dramatically increases distinct DC subsets, or DC precursors, in the blood. FL increases both the CD11c+ DC subset (48-fold) and the CD11c- IL-3R+ DC precursors (13-fold). In contrast, G-CSF only increases the CD11c- precursors (>7-fold). Freshly sorted CD11c+ but not CD11c- cells stimulate CD4+ T cells in an allogeneic MLR, whereas only the CD11c- cells can be induced to secrete high levels of IFN-alpha, in response to influenza virus. CD11c+ and CD11c- cells can mature in vitro with GM-CSF + TNF-alpha or with IL-3 + CD40 ligand, respectively. These two subsets up-regulate MHC class II costimulatory molecules as well as the DC maturation marker DC-lysosome-associated membrane protein, and they stimulate naive, allogeneic CD4+ T cells efficiently. These two DC subsets elicit distinct cytokine profiles in CD4+ T cells, with the CD11c- subset inducing higher levels of the Th2 cytokine IL-10. The differential mobilization of distinct DC subsets or DC precursors by in vivo administration of FL and G-CSF offers a novel strategy to manipulate immune responses in humans.

Influence of lymphocytes on the presence and organization of dendritic cell subsets in the spleen

Studies were undertaken to clarify the roles of individual leukocyte populations in maintaining the presence and organization of splenic dendritic cells (DCs). Using Abs specific for DC subsets, we found that the distinct types of DC maintained appropriate compartmentalization within the white pulp of lymphocyte-deficient mice despite an unusual overall distribution of DCs. Even in mice lacking both B and T lymphocytes, the central arteriole remained the structure around which T area DCs were organized. Marginal zone area DCs remained in a peripheral sheath excluded from the T area DCs. Additionally, we revealed an important role for splenic B cells in the presence and organization of marginal zone cells. B-deficient or B- and T-deficient mice lacked sialoadhesin+ marginal zone macrophages and lacked MAdCAM-1 expression in marginal zone reticular endothelial cells. Adoptive transfer of B lymphocytes induced MAdCAM-1 expression but failed to recruit marginal zone macrophages. Taken together, our results demonstrate that the arrival, localization, and persistence of DCs in spleen are events not solely dependent upon signals from the mature B and T cells or marginal zone macrophages. We suggest that specific stromal elements in the vicinity of the central arteriole are primarily responsible for providing directional cues to the DC.

Survival, maturation, and function of CD11c- and CD11c+ peripheral blood dendritic cells are differentially regulated by cytokines

Two types of dendritic cells (DC) are circulating in human blood and can be identified by their differential expression of the myeloid Ag CD11c. In this study, we show that CD11c- peripheral blood (PB)-DC correspond to plasmacytoid DC of lymphoid tissue not only by their surface Ag expression profile but, more impressively, by their peculiar ultramorphology. We also demonstrate that CD11c- and CD11c+ DC differ in the quality of their response to and in their requirement for certain cytokines. Freshly isolated CD11c- cells depend on IL-3 for survival and use autocrine or exogenous TNF-alpha as maturation signal, leading to the appearance of a highly dendritic phenotype, the up-regulation and redistribution of MHC class II from lysosomal compartments to the plasma membrane, the increased expression of costimulatory molecules, and the switch from a high Ag-processing to a low Ag-processing/potent accessory cell mode. Surprisingly, IL-4 efficiently killed freshly isolated CD11c- PB-DC, but did not impair the viability of CD11c+ PB-DC and, together with GM-CSF, induced maturation of these cells. A direct functional comparison revealed that neo-Ag-modified and subsequently matured CD11c- but to a lesser extent CD11c+ DC were able to prime naive Ag-specific CD4+ T cells. Our findings show that two diverse DC types respond to certain T cell-derived cytokines in a differential manner and, thus, suggest that suppression or activation of functionally diverse DC types may be a novel mechanism for the regulation of the quantity and quality of immune responses.

Bezafibrate as differentiating factor of human myeloid leukemia cells

Bezafibrate belongs to the class of fibric acid derivatives usually used as antihyperlipidemia agents. From the biochemical point of view, these drugs show intriguing properties which leads one to think they may promote a differentiation process in tumour cells. This new pharmacological activity of fibrates could partially depend on the induction of an oxidative stress. To test this hypothesis, the effect of bezafibrate, as well as of clofibric acid and gemfibrozil, on growth, functional and cytochemical characteristics of human leukaemia-derived cell lines HL-60, U-937 and K-562 has been studied in some details. The results show that bezafibrate, gemfibrozil and clofibric acid, do induce differentiation in human myeloid leukaemia cell lines as indicated by several differentiation markers. Moreover fibrates, in dose dependent manner, significantly alter the cell cycle distributions, mainly leading to G0/G1 phase increment and G2/M phase reduction. The differentiating activity of fibrates could have significant implications both for the pharmacotoxicological profile of this class of compounds and for the pathophysiology of neoplastic disease.

Priming effect of met-enkephalin and beta-endorphin on chemiluminescence, chemotaxis and CD11b molecule expression on human neutrophils in vitro

The opioid peptides are widely distributed throughout the body, and they are generated during stress and inflammatory reaction. Opioids are involved in the communication between the immune and neuroendocrine systems. In the present study we have investigated the ability of both met-enkephalin and beta-endorphin to stimulate and prime the human neutrophils for enhanced chemiluminescence (CL) and chemotaxis induced with fMLP, OZ or PMA. We have also tested the effect of beta-endorphin and met-enkephalin on CD11a, CD11b, CD18 and CD16 molecule expression on PMN in vitro. PMN from ten healthy donors were incubated in vitro with different concentrations of beta-endorphin or met-enkephalin, and the CL response was evaluated with luminometer. To assess the effect of opioid peptides on CD11a, CD11b, CD18 and CD16 molecule expression the whole blood samples were incubated with different concentrations of the opioids, then the white cells were labelled with respective PE-conjugated MoAb and evaluated by flow cytometry. We have shown that: (1) met-enkephalin and beta-endorphin at physiological concentrations relevant to that of in vivo (10(-8) and 10(-6) M) enhanced fMLP, PMA or OZ stimulated chemiluminescence and induced chemotactic response, (2) High concentrations of beta-endorphin (10(-3) M) or met-enkephalin (10(-5) M) decreased the CL response of PMN in vitro, (3) The opioid peptides at lower concentrations resulted in CD11b and CD18 molecule up-regulation on neutrophils. We may conclude that opioid peptides in physiological concentration are involved in neutrophil priming whereas in higher concentration exert immunosuppressive potency. Opioid peptides like inflammatory cytokines may prime the neutrophils inflammatory response.

Evidence for a role of IL-17 in organ allograft rejection: IL-17 promotes the functional differentiation of dendritic cell progenitors

IL-17 is a T cell-derived cytokine that stimulates stromal cells and macrophages to secrete proinflammatory cytokines. We hypothesized that IL-17 might play a role in alloimmune responses, and that interference with its activity might suppress allograft rejection. IL-17R:Fc or control IgG was added at the start of mouse MLR or was administered i.p. (100-500 microg/day) for different durations post-transplant to murine recipients of MHC-mismatched cardiac allografts. IL-17R:Fc (50-200 microg/ml) markedly inhibited T cell proliferation in vitro and significantly prolonged nonvascularized cardiac allograft median survival time from 13 to 20 days (100 microg/day; days 0 and 1) or to 19 days (100-300 microg/day; days 0-4). Survival of vascularized grafts was also extended significantly from 10.5 to 19 days by IL-17R:Fc (500 microg/day; days 0-6). To address a possible mechanism by which IL-17 may promote alloreactivity, we examined the influence of IL-17 on the differentiation and function of bone marrow-derived cells propagated in granulocyte-macrophage CSF with or without IL-4 to promote dendritic cell (DC) growth. A minor proportion of CD11c+ DC expressed the IL-17R. IL-17 promoted the maturation of DC progenitors, as evidenced by increased cell surface expression of CD11c, costimulatory molecules (CD40, CD80, CD86), and MHC class II Ag, and allostimulatory capacity. IL-17 had a lesser effect on the phenotype and function of more fully differentiated myeloid DC. These findings suggest a role for IL-17 in allogeneic T cell proliferation that may be mediated in part via a maturation-inducing effect on DC. IL-17 appears to be a novel target for therapeutic intervention in allograft rejection.

Effect of linoleic acid, linoleic acid anilide, and arachidonic acid on the expression of adhesion molecules on human neutrophils

The effects of linoleic acid, linoleic acid anilide, and arachidonic acid on the expression of CD11b/ CD18, CD11c/CD18 integrins and L-selectin on human neutrophils were studied by flow cytometry in a whole blood assay. None of these compounds had any effect on the basal expression of CD11b, CD11c, or L-selectin in the concentration range of 20-100 microM. However, linoleic acid at a concentration of 1000 microM slightly up-regulated CD11b and CD11c by a factor of 2.1 and 1.7, respectively. Linoleic acid, linoleic acid anilide, and arachidonic acid did not affect the formyl-methionyl-leucyl-phenylalanine induced up-regulation of CD11b or CD11c. However, linoleic acid and linoleic acid anilide slightly inhibited the phorbol myristate acetate (PMA)-induced expression of CD11b, which was decreased by 27 and 21% at concentrations of 100 and 1000 microM, respectively. Likewise, arachidonic acid at 40 microM inhibited the PMA-induced expression of CD11b by 19%. Our results suggest that linoleic acid, linoleic acid anilide, and arachidonic acid do not dramatically affect the expression of leukocyte adhesion molecules in a whole blood assay.

The 25-kDa soluble CD23 activates type III constitutive nitric oxide-synthase activity via CD11b and CD11c expressed by human monocytes

CD23, a low-affinity receptor for IgE, was recently shown to bind to CD11b and CD11c molecules on human monocytes. The 25-kDa soluble fragment of CD23 (sCD23), was tested for its capacity to elicit various signaling pathways in human monocytes. sCD23 was found to trigger an early increase in cGMP accumulation, through the generation of nitric oxide. This was a result of activating the L-arginine pathway, since the sCD23-mediated effect was inhibited in the presence of substituted nonmetabolizable L-arginine analogues. In addition, the increase in cGMP was suppressed by calcium chelators and inhibitors of the calcium/calmodulin complex, suggesting the involvement of a constitutive, calcium-dependent nitric oxide synthase (NOS). Indeed, the presence of an endothelial constitutive type III NOS mRNA was detected in nonactivated human monocytes, and the corresponding protein has been detected by flow cytometry. Moreover, sCD23 was shown to induce a calcium influx in monocytes, in accordance with an activation of a constitutive NOS through a transient increase in [Ca2+]i. As expected, these events were mimicked by mAbs against CD11b and CD11c, the macrophage receptors for CD23. In addition to these early events, sCD23 and the agonistic anti-CD11b and CD11c mAbs, which all trigger the release of proinflammatory mediators such as TNF-alpha, were shown to act through an NO-dependent process.

Surface adhesion molecule expression on human blood cells induced by vascular graft materials in vitro

The expression of surface adhesion molecules on granulocytes, monocytes (CD11a, CD11b, CD11c, CD18, L-selectin), and platelets (P-selectin, gpIIb-IIIa) was determined after incubation with different graft surfaces [expanded polytetrafluoroethylene (ePTFE) or woven Dacron]. Woven Dacron grafts upregulated the CD11b and CD11c surface antigens on both granulocytes and monocytes. Both graft materials demonstrated increased expression of CD11a and CD18 adhesion molecules on white blood cells at 30 min, followed by a downregulation. Maximum L-selectin expression was seen at 120 min on granulocytes and at 90 min on monocytes without differences between the graft materials. A rapid downregulation of gpIIb-IIIa complexes on platelets was noticed, while no expression of platelet P-selectin molecules was observed. In conclusion, both graft materials induced alteration of the white blood cell adhesion molecule expression, but the intensity and time course were dependent on the cell type and the graft material, suggesting that different mechanisms might be implicated. The expression of platelet surface antigens was less clearly influenced. The clinical significance of an enhanced cell surface antigen receptor expression caused by woven Dacron (CD11b, CD11c) has to be further studied. However, determination of adhesion molecule expression might offer possibilities to predict biocompatibility.

Protein tyrosine kinase activity and the influence of gender in phagocytosis and tumor necrosis factor secretion in alveolar macrophages and lung-recruited neutrophils

The role of tyrosine phosphorylation in endotoxin-induced phagocytic and tumor necrosis factor secretory responses was studied in rat alveolar macrophages and lung-recruited neutrophils. Exploration of sexual dimorphism in some aspects of these functions was also a specific aim. Male and female rats were injected intratracheally with endotoxin or saline. Two and a half hours later the animals were subjected to bronchoalveolar lavage, and alveolar macrophages and lung-recruited neutrophils were isolated. Circulating neutrophils of endotoxin-treated rats were also isolated at this time. Phagocytosis and CD11b/c and CD18 expression were measured by flow cytometry; tumor necrosis factor was measured with a cytotoxicity assay. Using the protein tyrosine kinase inhibitor AG126 and phosphotyrosine immunoblotting, we demonstrated that tyrosine phosphorylation is an important signaling pathway in the activation of these cells by endotoxin and that it is coupled to phagocytosis and tumor necrosis factor secretion, but not to beta 2 integrin expression. Conditioned medium of alveolar macrophages of endotoxin-injected rats upregulates phagocytosis by blood neutrophils of naive rats and this upregulating activity is tyrosine phosphorylation dependent. The substrates for tyrosine phosphorylation are different in alveolar macrophages and lung neutrophils, as are their sensitivities to AG126. Significant gender differences exist in the modulation of phagocytosis by inhibition of tyrosine phosphorylation and in tumor necrosis factor secretion by endotoxin-stimulated alveolar macrophages.

Effects of 1,25-dihydroxy vitamin D3 on all-trans retinoic acid sensitive and resistant acute promyelocytic leukemia cells

Following challenge of the acute promyelocytic leukemia (APL) cell line, NB4, with 1, 25 dihydroxy vitamin D3 (1, 25 D3), no increase in the expression of the monocytic surface markers, CD11c, CD14 and HLA-DR is observed. By contrast, 1, 25 D3 increases the expression of CD11b, an early myeloid marker and enhances adherence to plastic following priming of the cells with phorbol 12-myristate 13-acetate (PMA). NB4.306 and NB4.007/6, two all-trans retinoic acid-resistant cell lines originated from NB4 promyelocytes and lacking expression of a complete form of PML-RAR, are totally resistant to 1, 25 D3-dependent induction of CD11b. In addition, NB4.306 cells do not show enhanced plastic adherence following treatment with the vitamin D metabolite and PMA. NB4 and NB4.306 express similar amounts of the transcripts coding for the vitamin D3 receptor and the retinoid accessory receptors, RXR alpha and RXR beta, both in basal conditions and upon treatment with 1, 25 D3.

Modulation of ICAM-1 levels on U-937 cells and mouse macrophages by interleukin-1 beta and dexamethasone

Differentiation of U-937 cells with phorbol ester (10 nM) induced a time-dependent (24 h or 48 h) increase of adhesion molecules and lipocortin 1 expression on the cell surface. Stimulation with interleukin-1 beta for a further 16 h increased the levels of intercellular adhesion molecule-1, and this effect was inhibited by co-incubation with 0.1-1 microM dexamethasone. The effect of the glucocorticoid was not modified by addition of a specific anti-lipocortin 1 monoclonal antibody (mAb 1A, 5 micrograms/ml). This opposite modulatory role of interleukin-1 and dexamethasone on intercellular adhesion molecule-1 expression was also, for the first time, observed in vivo using mouse peritoneal macrophages: a four-fold increase in intercellular adhesion molecule-1 expression was measured after local administration of the cytokine (5 micrograms/kg) and this effect was greatly inhibited (> 70%) by co-injection with 1 microgram dexamethasone. In conclusion, modulation of intercellular adhesion molecule-1 expression by glucocorticoids is an effect independent endogenous lipocortin 1, and it is an in vivo feature of these potent anti-inflammatory drugs.

Granulocyte-colony stimulating factor, granulocyte-macrophage colony stimulating factor and interleukin 4 induce differentiation in the U-937 human monocytic leukemia cell line

We studied the effect of TPA, G-CSF, GM-CSF, conditioned medium from 5637 cells (CM5637) and IL-4 on U-937 cell line proliferation and differentiation. Flow cytometry analysis showed that the expression of the CD14 cell surface antigen, initially detected in 90% of the cells, decreased when the cells were cultured with either G-CSF, GM-CSF, CM5637, or IL-4. The CD11c expression only decreased by exposure to GM-CSF and IL-4. The cells also showed a decrease in alpha-naphthylesterase (alpha-NAE) activity and an increase in peroxidase (Px) activity in the GM-CSF supplemented cultures. Remarkable changes in cell morphology were also observed. IL-4 induced morphologic features resembling histiocytic-like cells positive for the expression of alpha-NAE and negative for Px. GM-CSF induced cells with pseudopods, negative for alpha-NAE expression and positive for Px. TPA effect on U-937 cells was similar to that observed with GM-CSF. No proliferative response was detected with any of the factors assayed. These results suggest that GM-CSF and IL-4 can promote distinct changes in the differentiative pathway of U-937 cells, as evidenced by the marked morphological, immunological and cytochemical changes observed in the cell cultures.

Expression of the p53 tumor suppressor gene induces differentiation and promotes induction of differentiation by 1,25-dihydroxycholecalciferol in leukemic U-937 cells

Leukemic U-937 cells, which lack normal p53, were stably transfected with a temperature-sensitive mutant of p53 to investigate the consequences for growth and differentiation. On induction of wild-type p53 activity at the permissive temperature, some of these cells underwent maturation as judged by the capacity for oxidative burst and the appearance of monocyte related cell surface molecules. Moreover, wild-type p53-expressing cells were more sensitive than p53-negative control cells to induction of differentiation by 1,25-dihydroxycholecalciferol; a twofold to fourfold increase of the fraction of cells showing signs of terminal maturation was observed when wild-type p53-expressing cells were incubated with 1,25-dihydroxycholecalciferol at concentrations that only slightly affected control cells. Whereas wild-type p53 activity per se induced maturation of certain cells, other underwent cell death judging from the reduced capability to exclude trypan blue and the appearance of fragmented DNA in flow cytometric analysis. The p53-induced cell death could be inhibited by incubation with 1,25-dihydroxy-cholecalciferol, but not all-trans retinoic acid. Thus, 1,25-dihydroxycholecalciferol, seemed to increase the survival of wild-type p53-expressing cells and to cooperate with wild-type p53 to induce differentiation. The data imply that p53-mediated maturation in U-937 cells depends on optimal regulation of signals for differentiation, survival and proliferation, and suggest a role for p53 in the differentiation induction of leukemic cells.

Granulocyte-macrophage colony-stimulating factor, phorbol ester, and sodium butyrate induce the CD11c integrin gene promoter activity during myeloid cell differentiation

To analyze the activity of the CD11c promoter during myeloid differentiation without the limitations of transient expression systems, we have stably transfected the myeloid U937 cell line with the pCD11C361-Luc plasmid, in which the expression of the firefly luciferase cDNA is driven by the CD11c promoter region -361/+43, previously shown to confer myeloid specificity to reporter genes. The stable transfectants (U937-C361) retained the ability to differentiate in response to phorbol-ester (PMA), sodium butyrate (SB), granulocyte-macrophage colony-stimulating factor (GM-CSF), and other differentiating agents. U937-C361 differentiation correlated with increased cellular luciferase levels, showing the inducibility of the CD11c promoter during myeloid differentiation and establishing the U937-C361 cells as a suitable system for studying the myeloid differentiation-inducing capacity of cytokines, growth, factors, and other biological response modifiers. Unexpectedly, the inducibility of the CD11c gene promoter showed distinct kinetics and magnitude on the PMA-, SB-, GM-CSF-triggered differentiation. Moreover, SB synergized with either PMA or GM-CSF in enhancing both the CD11c promoter activity and the cell surface expression of p150,95 on differentiating U937 cells. Furthermore, we showed the existence of a c-Myb-binding site at -85, the importance of the -99/-61 region in the CD11c promoter inducibility during PMA- or SB-triggered differentiation, and the dependency of the GM-CSF and PMA responsiveness of the CD11c promoter on an intact AP-1-binding site located at -60. These results, together with the lack of functional effect of mutations disrupting the Sp1-and Myb-binding sites within the proximal region of the CD11c promoter, indicate that the myeloid differentiation pathways indicated by SB and phorbol esters (or GM-CSF) activate a distinct set of transcription factors and show that the myeloid differentiation-inducibility of the CD11c gene maps to the -99/-53 proximal region of the promoter.

Regulation of expression of the LFA-1 and p150,95 leukocyte integrins: involvement of the CD11a and CD11c gene promoters

Human Lymphocyte Associated Antigen-1 (LFA-1, CD11a/CD18, alpha L/beta 2) and p150,95 (CD11c/CD18, alpha X/beta 2) are cell surface alpha/beta heterodimers that, together with Mac-1 (CD11b/CD18, alpha M/beta 2) comprise the leukocyte-restricted beta 2 subfamily of integrins. LFA-1 is the only integrin expressed on all leukocyte lineages while p150,95 is exclusively expressed on cells of the myeloid lineage and on activated B lymphocytes and natural killer cells. The expression of the leukocyte integrins is regulated during cell activation and differentiation by transcriptional mechanisms. To dissect the molecular basis for the tissue-restricted and developmentally regulated expression of LFA-1 and p150,95, the promoter regions of their corresponding alpha subunits (CD11a and CD11c) were isolated and functionally characterized. Both promoters lack TATA and CAAT boxes, but exhibit initiator-like sequences at their major transcriptional start sites. Transient expression of CD11a- and CD11c-based reporter gene constructs have demonstrated the involvement of both promoters in the tissue-specific expression of LFA-1 and p150,95. Furthermore, a combination of DNAse I protection experiments and mobility band shift assays have revealed the existence of numerous DNA-protein interactions at the proximal region of both promoters, some of which overlap with consensus binding sequences for known transcription factors and correlate with the pattern of expression of both integrins.

Antigen-driven induction of CD11c on intestinal intraepithelial lymphocytes and CD8+ T cells in vivo

Intraepithelial lymphocytes (IEL) of the intestinal epithelium represent a phenotypically and functionally distinct subpopulation of peripheral T cells. In this study, we report the production of a mAb, designated HL3, which exhibits reactivity with a subset of IEL. In differential screening assays HL3 reacted with 30 to 50% of IEL, but not with T cells of the thymus, spleen, or lymph nodes. Biochemical characterization revealed that the HL3 mAb recognized p150,95 (CD11c/CD18; CR4), a member of the beta 2-integrin family. Fluorescence flow cytometric analyses showed that p150,95 was expressed by TCR-alpha beta or TCR-gamma delta CD4-8+ IEL but not by CD4+8- IEL. Induction of graft-vs-host (GVH) disease resulted in up-regulation of p150,95 expression on donor-derived CD8+ T cells in the intestinal epithelium, as well as in the spleen and lymph nodes. GVH also induced MAC-1 (CD11b) expression on a subset of CD8+ lymph node T cells, but MAC-1 was not up-regulated on CD8+ IEL in this situation. In contrast, activation of identical T cell responders in vitro resulted in weak induction of p150,95 and MAC-1 expression. This result suggested that activation alone was insufficient for p150,95 up-regulation and that additional factors available in vivo were essential in this process. In the intestine, induction of p150,95 required the presence of intestinal flora as IEL from germfree mice lacked p150,95. Interestingly, gamma delta IEL expressing a non-IEL type transgenic TCR were also p150,95-, but exposure to Ag in vivo, but not in vitro, resulted in p150,95 induction. This result indicated that the constitutive expression of p150,95 on IEL is likely due to Ag stimulation via the TCR and not a bystander phenomenon. Overall, the results demonstrated p150,95 to be a hallmark of T cell activation in vivo and an indicator of ongoing antigen-specific T cell activation in the intestinal epithelium.