Critical role for serum opsonins and complement receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) in phagocytosis of Francisella tularensis by human dendritic cells (DC): uptake of Francisella leads to activation of immature DC and intracellular survival of the bacteria

Francisella tularensis is one of the most infectious human pathogens known. Although much has been learned about the immune response of mice using an attenuated live vaccine strain (LVS) derived from F. tularensis subspecies holarctica (Type B), little is known about the responses of human monocyte-derived immature dendritic cells (DC). Here, we show that optimal phagocytosis of LVS by DC is dependent on serum opsonization. We demonstrate that complement factor C3-derived opsonins and the major complement receptors expressed by DC, the integrins CR3 (CD11b/CD18) and CR4 (CD11c/CD18), play a critical role in this adhesion-mediated phagocytosis. LVS induced proinflammatory cytokine production and up-regulation of costimulatory surface proteins (CD40, CD86, and MHC Class II) on DC but resisted killing. Once taken up, LVS grew intracellularly, resulting in DC death. DC maturation and cytokine production were induced by direct contact/phagocytosis of LVS or interaction with soluble products of the bacteria, and enhanced activation was seen when LVS was pretreated with serum. Sonicated LVS and supernatants from LVS cultures were potent activators of DC, but LVS LPS failed to activate DC maturation or cytokine production. Serum-treated LVS rapidly induced (within 6 h) a number of cytokines including IL-10, a potent suppressor of macrophage functions and down-regulator of Th1-like responses and the Th1 response inducer IL-12. These results suggest that the simultaneous production of an activating (IL-12, IL-1beta, and TNF-alpha) and a suppressing (IL-10) cytokine profile could contribute to the immunopathogenesis of tularemia.

Serum amyloid p component does not circulate in complex with C4-binding protein, fibronectin or any other major protein ligand

Serum amyloid P component (SAP) is a pentameric plasma protein associated with all known kinds of amyloid. The normal physiological function of the protein has not been fully elucidated but it may be involved in clearance of cellular debris and in innate immunity. An important clue to its normal function is the identity of ligands bound to SAP in the circulation. It has been reported that all SAP is complexed with C4-binding protein (C4bp) but other studies have not been able to confirm this. We here study this issue by a combination of crossed immunoelectrophoresis (CIE), size exclusion chromatography, and native polyacrylamide electrophoresis and we show that SAP in serum - analysed under native analysis conditions and free of immobilizing antibodies - does not have any major protein ligand. However, when the protein is aggregated by immobilized antibodies, C4bp and fibronectin clearly bind to SAP. If circulating SAP under normal circumstances bind any protein ligand in vivo, our results strongly suggest that this only occurs to a minor extent.

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.

Loss of blood CD11c(+) myeloid and CD11c(-) plasmacytoid dendritic cells in patients with HIV-1 infection correlates with HIV-1 RNA virus load

Human blood contains at least 2 subpopulations of antigen-presenting dendritic cells (DCs) that can be differentiated by their expression of CD11c. Myeloid DCs (myDCs), which are CD11c(+), trap invading pathogens in the tissues and then migrate to lymphoid tissues where they stimulate pathogen-specific T-cell responses. Plasmacytoid DCs (pcDCs), which are CD11c(-), secrete interferon-alpha in response to viral infections. This study reports that in HIV-1 infection there is a progressive depletion of both these DC populations and that this correlates with an increasing HIV-1 plasma virus load. The median numbers of myDCs and pcDCs were 6978/mL and 9299/mL, respectively, in healthy male controls and 2298/mL and 1640/mL, respectively, in patients with more than 10(5) HIV-1 RNA copies/mL. Both DC populations expressed CD4, CCR5, and CXCR4. The findings suggest that loss of DCs in HIV infection may contribute to disease progression.

Regulation of in situ complement activation via the lectin pathway in patients with IgA nephropathy

The lectin pathway, which is initiated by mannose-binding lectin (MBL) and MBL-associated serine protease (MASP), is one of the possible routes to activate the complement cascade in immunoglobulin A (IgA) nephropathy. The purpose of this study was to elucidate the regulatory mechanism of the pathway. Levels of complement activation products and regulatory proteins were measured in sera from 27 patients with IgA nephropathy, and generation of fluid-phase complement activation products in the presence of pooled normal human serum was quantified to evaluate activation in vitro. Although there were no significant differences in the serum levels and in vitro activation between the MBL-MASP positive (n = 14) and negative (n = 13) groups, there were positive correlations between complement activation products (Bb fragment and C4d fragment) and regulatory proteins (factor H, C4-binding protein, and C1 inhibitor) in the MBL-MASP-positive group. Furthermore, immunohistochemical studies demonstrated glomerular deposition of the regulatory protein (C4-binding protein, alpha2-macroglobulin, and factor H) in all patients in the MBL-MASP-positive group. These findings suggest that the regulatory proteins control in situ complement activation via the lectin pathway immediately, and continuous activation due to inadequate control will lead to the advanced glomerular injury.

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.

Engagement of CD11b and CD11c beta2 integrin by antibodies or soluble CD23 induces IL-1beta production on primary human monocytes through mitogen-activated protein kinase-dependent pathways

beta2 integrins are involved in the recruitment of leukocytes to inflammatory sites and in cellular activation. We demonstrate that ligation of CD11b (Mac-1, CR3) or CD11c (p150, CR4) alpha chains of beta2 integrins by mAbs or soluble chimeric CD23 (sCD23) on human freshly isolated monocytes rapidly stimulates high levels of interleukin-1beta production. This induction takes place at the transcriptional level and is regulated by members of the mitogen-activated protein kinase (MAPK) family. Indeed, stimulation of monocytes through engagement of CD11b or CD11c results in the phosphorylation and activation of ERK1, ERK2, and p38/SAPK2 MAP kinases. U0126, a potent inhibitor of the upstream activator of ERK1/2, ie, MEK1/2, suppresses IL-1beta messenger RNA (mRNA) expression in a dose-dependent fashion, showing the implication of this pathway in the transcriptional control of IL-1beta production. On the other hand, inhibition of p38 by SB203580 indicates that this MAPK is involved in the control of IL-1beta production at both transcriptional and translational levels. Together these data demonstrate that ligation of CD11b and CD11c beta2 integrins by mAbs or sCD23 fusion proteins triggers the activation of 2 distinct MAPK signaling pathways that cooperate in controlling IL-1beta synthesis at different levels. (Blood. 2000;95:3868-3877)

The interaction between anticoagulant protein S and complement regulatory C4b-binding protein (C4BP)

An important mechanism of regulation of blood coagulation is the anticoagulant protein C pathway. In this pathway, the anticoagulant activity of activated protein C is increased by its cofactor protein S. The cofactor activity of protein S can be regulated by binding to complement regulatory C4b-binding protein (C4BP). The sites of interaction of protein S and C4BP are discussed.

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.

A CD1a+/CD11c+ subset of human blood dendritic cells is a direct precursor of Langerhans cells

Based on the relative expression of CD11c and CD1a, we have identified three fractions of dendritic cells (DCs) in human peripheral blood, including a direct precursor of Langerhans cells (LCs). The first two fractions were CD11c+ DCs, comprised of a major CD1a+/CD11c+ population (fraction 1), and a minor CD1a-/CD11c+ component (fraction 2). Both CD11c+ fractions displayed a monocyte-like morphology, endocytosed FITC-dextran, expressed CD45RO and myeloid markers such as CD13 and CD33, and possessed the receptor for GM-CSF. The third fraction was comprised of CD1a-/CD11c- DCs (fraction 3) and resembled plasmacytoid T cells. These did not uptake FITC-dextran, were negative for myeloid markers (CD13/CD33), and expressed CD45RA and a high level of IL-3Ralpha, but not GM-CSF receptors. After culture with IL-3, fraction 3 acquired the characteristics of mature DCs; however, the expression of CD62L (lymph node-homing molecules) remained unchanged, indicating that fraction 3 can be a precursor pool for previously described plasmacytoid T cells in lymphoid organs. Strikingly, the CD1a+/CD11c+ DCs (fraction 1) quickly acquired LC characteristics when cultured in the presence of GM-CSF + IL-4 + TGF-beta1. Thus, E-cadherin, Langerin, and Lag Ag were expressed within 1 day of culture, and typical Birbeck granules were observed. In contrast, neither CD1a-/CD11c+ (fraction 2) nor CD1a-/CD11c- (fraction 3) cells had the capacity to differentiate into LCs. Furthermore, CD14+ monocytes only expressed E-cadherin, but lacked the other LC markers after culture in these cytokines. Therefore, CD1a+/CD11c+ DCs are the direct precursors of LCs in peripheral blood.

Depletion in blood CD11c-positive dendritic cells from HIV-infected patients

OBJECTIVES

To quantify blood dendritic cells from HIV-positive patients and to study the expression of functional molecules, in relation to HIV viral load, CD4 cell counts and antiretroviral treatment.

DESIGN AND METHODS

Three-colour flow cytometry analysis was used to quantify blood dendritic cells without previous isolation from whole blood and to study the expression of functional molecules (MHC class II, CD11c, CD83, CD86) by dendritic cells from 30 HIV-positive patients, 15 of whom were treated with combined antiretroviral therapy (viral loads from undetectable to 5.4 log copies/ml, CD4 cell counts 1-1895 cells/mm3) and 11 non-infected controls.

RESULTS

The median proportion of blood dendritic cells from HIV-positive patients was significantly decreased when the plasma viral load was above 200 copies/ml: 0.2% (0.1-1.1, n = 19) compared with 0.4% (0.2-0.8, n = 11) in patients with undetectable viral load whether they were treated or not, and to 0.4% (0.2-1.3, n = 11) in controls (P = 0.02). A major decrease of the CD11c positive dendritic cells was observed in all HIV-positive samples, with only 18% (mean; range: 0.3-80%, median 4.2%) compared with 44% (11-70%, median 42%) of control dendritic cells (P = 0.0006). In contrast, the proportion of dendritic cells expressing CD86, was slightly higher in HIV-positive patients than in controls (P = 0.03).

CONCLUSIONS

The decreased proportion of blood dendritic cells correlated with virus replication and the lack of dendritic cells expressing CD11c are the first evidence of strong dendritic cell alterations in HIV-positive patients. Although the proportion of blood dendritic cells are in the normal range in treated HIV-positive patients with undetectable viral load, the CD11c alterations persist indicating that antiretroviral therapy might only partly correct the alterations of the circulating dendritic cells.

Neonatal neutrophil activation is a function of labor length in preterm infants

To understand better the development of the neonatal immune system, we evaluated the role of labor length, gestational age, and mode of delivery on the expression of the neonatal neutrophil cell surface antigens CD11b, CD11c, CD15, CD33, and CD66b in premature newborns. Peripheral blood samples from 68 apparently healthy preterm infants were obtained within 12 h of birth and incubated with MAb to the CD antigens. Samples were lysed, fixed, and analyzed by flow cytometry. Multivariate analysis was used to study the simultaneous effect of the labor length and gestational age on the neonatal neutrophil cell surface antigen expression. A positive correlation was demonstrated between neutrophil antigen expression and labor length (p < 0.001-0.026) but not with the mode of delivery (p = 0.191-0.638). There was no significant correlation between expression of neutrophil antigens and gestational age at delivery (p = 0.057-0.866), except for CD15 (p = 0.010). Our results indicate labor length is a significant factor in neonatal neutrophil activation at birth. These findings are independent of gestational age in preterm newborns. Mode of delivery does not seem to influence neonatal neutrophil activation. The neutrophils of premature infants can be activated antenatally and/or during labor.

Changes in adhesion molecule expression and oxidative burst activity of granulocytes and monocytes during open-heart surgery with cardiopulmonary bypass compared with abdominal surgery

Cardiac and major abdominal surgery are associated with granulocytosis in peripheral blood. The purpose of the present study was to describe the granulocyte and monocyte oxidative burst and the expression of adhesion molecules following cardiac surgery with cardiopulmonary bypass and abdominal surgery. The ability to respond with an oxidative burst was measured by means of flow cytometry using 123-dihydrorhodamine. The adhesion molecules CD11a/CD18, CD11c/CD18, CD44 were measured using monoclonal antibodies. Blood samples from eight patients undergoing open-heart surgery were taken before surgery, 1, 5, 10 and 20 min after aortic clamping, and then 1, 5, 10 and 20 min and 1, 2 and 3 h after declamping. Samples from eight patients undergoing abdominal surgery were taken before surgery, at the end of surgery, and 2 and 3 h post-operatively. A decrease in number of granulocytes and monocytes during cardiopulmonary bypass was observed. The percentage of CD11a-positive granulocytes increased from 30% pre-operatively to 75% following cardiopulmonary bypass, while CD44-positive granulocytes increased from 5% to 13%. Despite the extent of the changes, these were not significant. The oxidative burst of the granulocytes and monocytes decreased after declamping to 15% and 27% of initial values in vitro. Several hours after surgery, there was no significant difference between the two groups. These results can be explained by a granulocyte and monocyte refractory response developing subsequent to an increased per-operative oxidative burst activity, and the induction of adhesion molecules on granulocytes associated with the cardiopulmonary bypass and surgery. In conclusion, open-heart surgery with cardiopulmonary bypass was associated with a rapid and pronounced activation of leukocytes which may play a role in reperfusion injury.

Competitive binding of low molecular mass heparin-tyramine fluorescein-5-isothiocyanate and unlabeled glycosaminoglycans to leukocytes

Antithrombotic, antiarteriosclerotic, and anti-inflammatory actions of heparins may be mediated by binding of heparin to leukocytes. To get the first information on this hypothesis, fluorescein-labeled LMMH-tyramine has been used (LMMH-tyramine-FITC) to analyze the binding of GAGs to lymphocytes, monocytes, or granulocytes. The fluorescence intensity on leukocytes was quantified by flow cytometry analysis. LMMH-tyramine-FITC bound dose dependently to lymphocytes, monocytes, and granulocytes. PE-labeled CD 11c antibodies identified the specificity of the binding of LMMH-tyramine-FITC to granulocytes. UFH and LMMH displaced LMMH-tyramine-FITC dose dependently from leukocytes. Equimolar ratios of LMMH and LMMH-tyramine-FITC revealed a 50% displacement of the labeled compound, indicating the specific binding by the polysaccharide chain. The synthetic pentasaccharide was 10-fold and dermatan sulfate 100-fold less effective than UFH in displacing LMMH-tyramine-FITC from leukocytes. The data indicate that negatively charged GAGs bind to the surface of lymphocytes, monocytes, and granulocytes. By decreasing the number of negatively charged groups of GAGs, the binding to the surface of leukocytes is decreased. The data obtained with the synthetic pentasaccharide indicate a binding of GAGs to the surface of leukocytes, independently of AT III. The cellular binding of heparins may significantly contribute to its antithrombotic and other biologic activities.