Two distinct pathways of human macrophage differentiation are mediated by interferon-gamma and interleukin-10

CD16 is indispensable for antibody-dependent cellular cytotoxicity by human monocytes

Antibody-dependent cellular cytotoxicity (ADCC) is exerted by immune cells expressing surface Fcγ receptors (FcγRs) against cells coated with antibody, such as virus-infected or transformed cells. CD16, the FcγRIIIA, is essential for ADCC by NK cells, and is also expressed by a subset of human blood monocytes. We found that human CD16− expressing monocytes have a broad spectrum of ADCC capacities and can kill cancer cell lines, primary leukemic cells and hepatitis B virus-infected cells in the presence of specific antibodies. Engagement of CD16 on monocytes by antibody bound to target cells activated β2-integrins and induced TNFα secretion. In turn, this induced TNFR expression on the target cells, making them susceptible to TNFα-mediated cell death. Treatment with TLR agonists, DAMPs or cytokines, such as IFNγ, further enhanced ADCC. Monocytes lacking CD16 did not exert ADCC but acquired this property after CD16 expression was induced by either cytokine stimulation or transient transfection. Notably, CD16+ monocytes from patients with leukemia also exerted potent ADCC. Hence, CD16+ monocytes are important effectors of ADCC, suggesting further developments of this property in the context of cellular therapies for cancer and infectious diseases.

Xuebijing injection improves the respiratory function in rabbits with oleic acid-induced acute lung injury by inhibiting IL-6 expression and promoting IL-10 expression at the protein and mRNA levels

Xuebijing injection is a complex herbal medicine, and clinical and experimental studies have shown that it has a significant effect on acute respiratory distress syndrome and multiple organ dysfunction syndrome. However, the majority of studies regarding Xuebijing injection have focused on serum inflammatory factors, and few studies have been carried out from the perspective of the protein and mRNA expression of inflammatory cytokines. In this study, 60 healthy rabbits of mixed gender were randomly assigned to a normal control group (CG), oleic acid group (model group; MG) and oleic acid + Xuebijing injection group (treatment group; TG). Rabbits of the CG were treated with normal saline through the ear vein, rabbits of the MG were injected with oleic acid (0.4 ml/kg) and rabbits of the TG received 0.4 ml/kg oleic acid + 10 ml/kg Xuebijing injection. Blood samples were collected from the common carotid artery of all rabbits of all groups 1 h after the ear vein was injected with the corresponding reagent, and was used to measure the arterial partial pressure of oxygen (PaO₂) and of carbon dioxide (PaCO₂). The activity of myeloperoxidase (MPO) was tested, and the protein and mRNA expression levels of interleukin (IL)-6 and IL-10 were determined. Rabbits of the MG exhibited evident respiratory dysfunction (PaO₂ and PaCO₂ were low), histopathological lung damage and overactive inflammatory responses (the expression of the proinflammatory cytokine IL-6 and the anti-inflammatory cytokine IL-10 was increased at the protein and mRNA levels). Following the administration of the Xuebijing injection, the inflammatory response of the rabbits was significantly reduced. Xuebijing injection raised PaO₂ and PaCO₂, weakened the activity of MPO in the lung tissue, downregulated the expression of the proinflammatory cytokine IL-6 and further increased the expression of the anti-inflammatory cytokine IL-10. These results demonstrated that Xuebijing injection improved the respiratory function of rabbits with acute oleic acid-induced lung injury by inhibiting IL-6 expression and promoting IL-10 expression.

Cytokine production is altered in monocytes from children with hemolytic uremic syndrome

PURPOSE

The interaction of Shiga toxin (Stx) and/or lipopolysaccharide (LPS) with monocytes (Mo) may be central to the pathogenesis of hemolytic uremic syndrome (HUS), providing the cytokines necessary to sensitize endothelial cells to Stx action. We have previously demonstrated phenotypical alterations in Mo from HUS patients, including increased number of CD16+ Mo. Our aim was to investigate cytokine production in Mo from HUS patients.

METHODS

We evaluated TNF-α and IL-10 intracellular contents and secretion in the different Mo subsets in mild (HUS 1) and moderate/severe (HUS 2 + 3) patients. As controls, we studied healthy (HC) and infected children (IC). We also studied Mo responsive capacity towards LPS, measuring the modulation of Mo surface molecules and cytokine production.

RESULTS

In basal conditions, the intracellular measurement of TNF-α and IL-10 revealed that the highest number of cytokine-producing Mo was found in HUS 2 + 3 and IC, whereas LPS caused a similar increase in TNF-α and IL-10-producing Mo for all groups. However, when evaluating the release of TNF-α and IL-10, we found a diminished secretion capacity in the entire HUS group and IC compared to HC in basal and LPS conditions. Similarly, a lower Mo response to LPS in HUS 2 + 3 and IC groups was observed when surface markers were studied.

CONCLUSION

These results indicate that Mo from severe cases of HUS, similar to IC but different to mild HUS cases, present functional changes in Mo subpopulations and abnormal responses to LPS.

A new strategy to induce effective antitumour response in vitro and in vivo

To induce Her2-specific cell immune response, we used xenogeneic antigen rat neu L2-S2 domains as the vaccine antigen. The antigenic protein was engineered as a chimeric protein with human IgG1 Fc region (neu-Fc). Neu-Fc could stimulate the cell proliferation in mixed lymphocyte reaction effectively. Simultaneous neu-Fc and IFN-gamma stimulation dramatically elevated IL-12 secretion and reduced IL-10 production in PBMC. To further augment the activating effects on Th1-type response, Bacille Calmette-Guerin (BCG) was utilized as a non-specific stimulus. Neu-Fc, IFN-gamma and BCG costimulation exhibited the most conspicuous effects on the reversal of the Th1-type inhibitory effects by MCF-7 cell supernatant compared with neu-Fc alone or IFN-gamma and BCG costimulation. The lytic activity of effector cells to Her2 overexpressing cells was greatly promoted by neu-Fc, IFN-gamma and BCG stimulation simultaneously. Neu-Fc led to considerable retardation in EMT6/Her2 tumour growth in Balb/c mice. IFN-gamma and BCG efficiently enhanced the antitumour activity. A large amount of inflammatory cells were found to be accumulated in the tumour tissues or surrounded tumours in mice treated with neu-Fc, IFN-gamma and BCG but no inflammatory cell infiltration was observed in control tumours, indicating that the strategy is potent enough to support the initiation and propagation of tumour-specific immune response in an established tumour and generate a proinflammatory environment.

Involvement of the fractalkine pathway in the pathogenesis of childhood hemolytic uremic syndrome

Thrombotic microangiopathy and acute renal failure are cardinal features of postdiarrheal hemolytic uremic syndrome (HUS). These conditions are related to endothelial and epithelial cell damage induced by Shiga toxin (Stx) through the interaction with its globotriaosyl ceramide receptor. However, inflammatory processes contribute to the pathogenesis of HUS by sensitizing cells to Stx fractalkine (FKN), a CX(3)C transmembrane chemokine expressed on epithelial and endothelial cells upon activation, is involved in the selective migration and adhesion of specific leukocyte subsets to tissues. Here, we demonstrated a selective depletion of circulating mononuclear leukocytes expressing the receptor for FKN (CX(3)CR1) in patients with HUS. We found a unique phenotype in children with HUS distinct from that seen in healthy, uremic, or infected controls, in which monocytes lost CX(3)CR1, down-modulated CD62L, and increased CD16. In addition, the CD56(dim) natural killer (NK) subpopulation was decreased, leading to an altered peripheral CD56(dim)/CD56(bright) ratio from 10.0 to 4.5. It is noteworthy that a negative correlation existed between the percentage of circulating CX(3)CR1(+) leukocytes and the severity of renal failure. Finally, CX(3)CR1(+) leukocytes were observed in renal biopsies from patients with HUS. We suggest that the interaction of CX(3)CR1(+) cells with FKN present on activated endothelial cells may contribute to renal injury in HUS.

Diminished response to interleukin-10 and reduced antibody-dependent cellular cytotoxicity of cord blood monocyte-derived macrophages

Monocyte-derived macrophage (MPhi) subsets are generated by antagonistic induction pathways. A helper MPhi-type (Mh-MPhi) is induced by interferon gamma (IFN-gamma), whereas a cytotoxic MPhi-type (Mc-MPhi), induced by interleukin-10 (IL-10), is a potent mediator of antibody-dependent cellular cytotoxicity (ADCC). Compared with MPhi from healthy adults [peripheral blood monocyte-derived macrophages (PBMPhi)], cord blood MPhi (CBMPhi) were found less capable of generating Mh-MPhi. Here we tested the hypothesis that their generation of Mc-MPhi via IL-10 is also impaired. MPhi surface markers were phenotyped. IL-10 protein and mRNA production were detected after stimulation [alphaCD3 monoclonal antibody (mAb)]. CBMPhi or PBMPhi were co-cultured with MPhi-depleted mononuclear cells of adults and CD4-targeting antibodies as models for ADCC were added. In cord blood, we found diminished alphaCD3-induced IL-10 protein and mRNA production (p < 0.05 versus adults). Basal CD16 and HLA-DR expressions on CBMPhi of preterm and full-term neonates were lower (p < 0.05 versus PBMPhi). IL-10 had reduced effects on CD16 up- and HLA-DR down-modulation on CBMPhi (p < 0.05 versus PBMPhi). CD4-directed receptor modulation and deletion were reduced in the presence of CBMPhi (p < 0.05 versus PBMPhi). IL-10 failed to enhance their ADCC capacity, which was in contrast to PBMPhi (p < 0.05). These data suggest that CBMPhi have an impaired cytotoxic capacity via lower sensitivity toward IL-10.

A new method to quantify phagocytosis and intracellular degradation using green fluorescent protein-labeled Escherichia coli: comparison of cord blood macrophages and peripheral blood macrophages of healthy adults

Interactions between innate and adaptive immune functions in neonatal macrophages (MPhi) are still unclear. We therefore established a method to quantify bacterial phagocytosis and intracellular degradation, using green fluorescent protein (GFP)-labeled Escherichia coli in combination with phenotypic analysis. The kinetics of the proportion of phagocyting MPhi, phagocytosed bacteria per MPhi, and bacterial degradation were comparable for cord blood MPhi of term neonates and MPhi of healthy adults. Phenotyping revealed CD14 and CD16 to be down-modulated within minutes. GFP-labeled E. coli may be useful tools to further study MPhi subpopulations and determinants of phagocytosis in cord blood MPhi.

Differential expression of function-related antigens on blood monocytes in children with hemolytic uremic syndrome

Monocytes (Mo) mediate central functions in inflammation and immunity. Different subpopulations of Mo with distinct phenotype and functional properties have been described. Here, we investigate the phenotype and function of peripheral Mo from children with hemolytic uremic syndrome (HUS). For this purpose, blood samples from patients in the acute period of HUS (HUS AP) were obtained on admission before dialysis and/or transfusion. The Mo phenotypic characterization was performed on whole blood by flow cytometry, and markers associated to biological functions were selected: CD14 accounting for lipopolysaccharide (LPS) responsiveness, CD11b for adhesion, Fc receptor for immunoglobulin G type I (FcgammaRI)/CD64 for phagocytosis and cytotoxicity, and human leukocyte antigen (HLA)-DR for antigen presentation. Some of these functions were also determined. Moreover, the percentage of CD14+ CD16+ Mo was evaluated. We found that the entire HUS AP Mo population exhibited reduced CD14, CD64, and CD11b expression and decreased LPS-induced tumor necrosis factor production and Fcgamma-dependent cytotoxicity. HUS AP showed an increased percentage of CD14+ CD16+ Mo with higher CD16 and lower CD14 levels compared with the same subset from healthy children. Moreover, the CD14++ CD16- Mo subpopulation of HUS AP had a decreased HLA-DR expression, which correlated with severity. In conclusion, the Mo population from HUS AP patients presents phenotypic and functional alterations. The contribution to the pathogenesis and the possible scenarios that led to these changes are discussed.

Non-responsiveness to hepatitis B surface antigen vaccines is not caused by defective antigen presentation or a lack of B7 co-stimulation

The mechanisms causing non-responsiveness to hepatitis B surface antigen (HBsAg) vaccines in man remain elusive. The increased incidence of non-responsiveness in subjects with HLA-DR3(+) or -DR7(+) haplotypes suggests that immune response mechanisms governed by genes of the MHC are involved. Homozygotes for these two haplotypes are found almost exclusively in the non-responder (NR) population. It is conceivable that antigen-presenting cells (APC) of NR are defective in the uptake of HBsAg and that they are unable to present this Ag adequately. Previously, we demonstrated that DR2(+), DR7(+) and DP4(+) NR were able to present HBsAg. In the present paper we demonstrate that six DR0301(+) NR, five of which are homozygous for this marker, were able to take up, process and present HBsAg to HBsAg-specific, DR0301-restricted T cell lines. Non-fractionated peripheral blood mononuclear cells (PBMC) from the DR0301(+) NR did not proliferate to HBsAg in vitro, whereas they proliferated vigorously upon stimulation with tetanus toxoid, thus ruling out the presence of a generalized immunodeficiency. We therefore conclude that HLA-DR0301(+) NR vaccinees are not deficient in their HBsAg-presentation. Because it was demonstrated that recently activated T cells can apparently bypass the requirement for B7, we may have overlooked the role of the B7-co-stimulation in our set-up that used HBsAg-specific T cell lines. Therefore we examined the expression of B7 co-stimulatory molecules on NR-APC. CD86 was normally present on these cells and was not down-regulated after culturing the PBMC in the presence of HBsAg. We conclude that CD86 expression on CD14(+) monocytes of DR0301- and DR07-homozygous poor responders is not deficient and cannot be the mechanism underlying the non-responsiveness of these subjects.

Effect of dexamethasone on B7 regulation and T cell activation in neonates and adults

The safety of dexamethasone for neonates has been questioned, partly because of its multiple unspecific effects on the immune system. Specific effects of dexamethasone on co-stimulatory and immune suppressive functions of neonatal compared with adult macrophages (MPhi) are not known. We evaluated the effect of dexamethasone on the expression and regulation of MPhi B7 family receptors (B7-1, CD80; B7-2, CD86) and on their ability to co-stimulate T cells. Cord blood macrophages (CBMPhi) and MPhi from healthy adults (PBMPhi) were isolated, and cell surface markers were phenotyped by flow cytometry. In tissue culture, cells were exposed to dexamethasone, interferon-gamma (IFN-gamma), cAMP, or a T cell mitogen (alphaCD3) and examined for their capacity to activate or destroy T cells. CBMPhi were less able to up-regulate CD80 and CD86 than PBMPhi (p < 0.05). Dexamethasone inhibited the up-regulation of CD80, CD86, and HLA-DR on PBMPhi and even more so on CBMPhi (p < 0.05 versus PBMPhi for CD80 and CD86). In the presence of dexamethasone, stimulation with alphaCD3 MAb enhanced cytotoxic functions of PMBMPhi and CB(mu)phi with an increase in deleted T cells, a reduced fraction of enlarged T cells, and an inhibition of T cell CD28 up-regulation, which again were more pronounced with CBMPhi (p < 0.05 versus PBMPhi). In conclusion, neonatal MPhi are exquisitely sensitive to the inhibitory effects of dexamethasone on B7 expression. Although perhaps producing the desired therapeutic effect, dexamethasone may do so in newborns at the expense of a near complete paralysis of MPhi-dependent T cell function.

Expression and regulation of B7 family molecules on macrophages (MPhi) in preterm and term neonatal cord blood and peripheral blood of adults

BACKGROUND

Macrophage (MPhi) receptors of the B7 family (CD80, CD86) play a crucial role in T cell activation: the lack of costimulation leads to anergy or apoptosis of reactive T cells. MPhi may differentiate into different subsets, the balance of which defines MPhi-dependent T cell reactions. The aim of this study was to examine neonatal and adult T cell response with respect to the costimulatory MPhi-potential in order to identify molecular predictors for the neonatal immune defense.

METHODS

MPhi from peripheral blood (PBMPhi) or cord blood (CBMPhi) were stimulated with interferon-gamma (IFN-gamma), cyclic adenosine monophosphate (cAMP), CD40 ligand (CD40L), or alphaCD3.

RESULTS

As compared to PBMPhi, CBMPhi showed a significantly decreased upregulation of CD80 and/or CD86 after stimulation with IFN-gamma, cAMP, CD40L, and alphaCD3. Accordingly, the proliferative T cell response was impaired in the presence of CBMPhi. The fraction of T cells that underwent cell death was higher, and blast formation was significantly lower than that observed in the presence of PBMPhi.

CONCLUSIONS

CBMPhi, as compared to PBMPhi, delivered fewer costimulatory but more cytotoxic signals to T cells. These observations suggest that MPhi are one factor explaining the suboptimal immune defense of neonates and their increased susceptibility to infection. Using the costimulatory MPhi-potential as a predictor for immune responses requires a separate reference value system in neonatology.

Interferon-gamma switches monocyte differentiation from dendritic cells to macrophages

Human monocytes differentiate into dendritic cells (DCs) or macrophages according to the nature of environmental signals. Monocytes stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF) plus interleukin 4 (IL-4) yield DCs. We tested here whether interferon-gamma (IFN-gamma), a potent activator of macrophages, may modulate monocyte differentiation. Addition of IFN-gamma to IL-4 plus GM-CSF-stimulated monocytes switches their differentiation from DCs to CD14(-)CD64(+) macrophages. IFN-gamma increases macrophage colony-stimulating factor (M-CSF) and IL-6 production by IL-4 plus GM-CSF-stimulated monocytes by acting at the transcriptional level and acts together with IL-4 to up-regulate M-CSF but not IL-6 production. IFN-gamma also increases M-CSF receptor internalization. Results from neutralizing experiments show that both M-CSF and IL-6 are involved in the ability of IFN-gamma to skew monocyte differentiation from DCs to macrophages. Finally, this effect of IFN-gamma is limited to early stages of differentiation. When added to immature DCs, IFN-gamma up-regulates IL-6 but not M-CSF production and does not convert them to macrophages, even in the presence of exogenous M-CSF. In conclusion, IFN-gamma shifts monocyte differentiation to macrophages rather than DCs through autocrine M-CSF and IL-6 production. These data show that IFN-gamma controls the differentiation of antigen-presenting cells and thereby reveals a new mechanism by which IFN-gamma orchestrates the outcome of specific immune responses.

Epstein-Barr virus encoded interleukin-10 inhibits HLA-class I, ICAM-1, and B7 expression on human monocytes: implications for immune evasion by EBV

Monocytes and macrophages play a central role in viral infections, as a target for viruses and in activation of both innate and adaptive immune responses. Epstein-Barr virus (EBV) has evolved elaborate strategies to dampen the immune system and to persist within the host. There is evidence that the product of the BCRF-1 open reading frame of EBV, viral interleukin-10 (vIL-10), inhibits the capacity of monocytes/macrophages to induce T cell activation, but the full mechanism of this effect is unknown. To determine whether this effect might involve modulation of the expression of accessory molecules known to be important in T cell activation, we analyzed by flow cytometry the influence of vIL-10 on the basal as well as on IFN-gamma-induced up-regulation of HLA molecules, ICAM-1, and two members of the B7 family B7.1 (CD80) and B7.2 (CD86) at the surface of human monocytes. Viral IL-10 in a concentration-dependent manner inhibited both basal- and IFN-gamma-induced HLA-class II, ICAM-1 (basal levels of ICAM-2 and ICAM-3 is unaffected), CD80, and CD86 up-regulation when added simultaneously with IFN-gamma. In contrast, complete inhibition of HLA-class I expression on monocytes/macrophages occurred only when vIL-10 was present 2 h prior to the addition of IFN-gamma, implying that vIL-10 affects an early step in the IFN-gamma signaling pathway. As both monocytes and macrophages can be infected by EBV, we propose that vIL-10-mediated impairment of monocyte/macrophage antigen-presenting function could help the virus-infected cells to avoid detection by the host's T cells on one hand and contribute to its immunosuppressive properties on the other.

High level expression and purification of the Epstein-Barr virus encoded cytokine viral interleukin 10: efficient removal of endotoxin

To characterize the structural and functional properties of viral interleukin 10 (vIL-10), its cDNA was cloned into the bacterial expression vector pMAL-c2, which directs the synthesis of the inserted gene as a fusion protein with maltose binding protein (MBP). The MBP-vIL-10 fusion protein was expressed in Escherichia coli and purified from cell lysates using amylose resin chromatography. Viral interleukin 10 (IL-10) was released from the fusion protein by cleavage with the proteolytic enzyme factor Xa. We show that vIL-10 will bind to heparin and use this property to purify vIL-10 from factor Xa cleaved products and trace contaminants using heparin agarose chromatography. A simple one-step procedure is described for the removal of endotoxins from heavily contaminated vIL-10 preparations. The protocol exploits the high binding affinity of MBP for amylose resin or vIL-10 for heparin and the ability of Triton-X114 to dissociate endotoxins from proteins. The biological activity of purified vIL-10 was demonstrated through its ability to inhibit interferon gamma (IFN-gamma) production by mitogen activated peripheral blood mononuclear cells and to down-regulate HLA-class II expression on activated monocytes/macrophages. The availability of an efficient expression and purification strategy for vIL-10 together with appropriate assays will contribute to a greater understanding of how vIL-10 has evolved to retain and modify those activities of cellular IL-10 best suited for Epstein-Barr virus (EBV)'s specialized niche within the host.

Interleukin-10 induces macrophage apoptosis and expression of CD16 (FcgammaRIII) whose engagement blocks the cell death programme and facilitates differentiation

The development of monocytes into macrophages is regulated by helper T cells (Th) cells and, vice versa, the differentiation of Th cells into Th1 and Th2 is regulated by macrophages. Herein we examined the role of the Th2 cytokine, interleukin-10 (IL-10), on the development of macrophages. IL-10 is known to block the expression of antigen-presenting major histocompatibility complex (MHC) II and of costimulatory B7 molecules but it induces the expression of FcRs, especially the FcgammaRIII (CD16). The expression of CD16 enables the macrophage to carry out antibody-dependent cell-mediated cytotoxicity (ADCC) functions. However, this differentiation step is largely undercut by the capacity of IL-10 to induce macrophage apoptosis before the process of differentiation ensues. We found that the negative effect of IL-10 on the survival of macrophages is reversed in an environment that contains immunoglobulin G (IgG). IgG, especially when immune complexed with antigen, stimulates CD16 to transmit survival signals in macrophages which enable them to complete the differentiation process into CD16+ cells. Thus, IL-10 suppresses macrophage accumulation in healthy tissues where IgG is absent, and facilitates macrophage accumulation and differentiation in tissues that contain IgG, for example inflamed tissues or tissues that present autoreactive antibodies.

CD14+CD16+ monocyte subpopulation in Kawasaki disease

Kawasaki disease (KD) is an acute febrile illness caused by vasculitis, occurring in early childhood. We have demonstrated that the activation of monocytes/macrophages plays a central role during acute KD. Recently, it has been reported that the CD14+CD16+ monocyte subpopulation plays a more important role in inflammation. In this study, we investigated the peripheral blood CD14+CD16+ monocyte subpopulation by flow cytometry, and serum levels of IL-10 and IL-12 using a sandwich ELISA in 28 KD patients. We also investigated this subpopulation in patients with bacterial infections, mononucleosis and anaphylactoid purpura, since the cause of KD remains unknown. We observed an increase in the number of CD14+CD16+ monocytes with acute KD, which was a positive correlation with C-reactive protein levels, and we observed only the patients with severe bacterial infections had increased this subpopulation during the acute stage among control diseases. In addition, we found that the serum levels of IL-10, but not IL-12, were higher during acute KD. These data suggest that increased peripheral blood CD14+CD16+ monocytes are part of the regulatory system of monocyte function during acute KD.

Heparin and heparan sulfate bind interleukin-10 and modulate its activity

Glycosaminoglycans (GAG) are a group of negatively charged molecules that have been shown to bind and directly regulate the bioactivity of growth factors and cytokines such as basic fibroblast growth factor, transforming growth factor-β, IL-7, and interferon-γ. The ability of GAG to interact with human IL-10 (hIL-10) and the effect of these interactions on its biologic activity were analyzed. It was demonstrated by affinity chromatography that hIL-10 binds strongly to heparin–agarose at physiological pH. Biosensor-based binding kinetic analysis indicated an equilibrium dissociation constant, Kd, of 54 nmol/L for this interaction. Human IL-10 stimulated CD16 and CD64 expression on the monocyte/macrophage population within peripheral blood mononuclear cells, with optimal concentrations between 1 and 10 ng/mL. Soluble heparin, heparan sulfate, chondroitin sulfate, and dermatan sulfate were shown to inhibit the hIL-10–induced expression of CD16 and CD64 in a concentration-dependent manner. Heparin and heparan sulfate were most effective with IC50 values of 100 to 500 μg/mL. Considerably higher concentrations of dermatan sulfate and chondroitin 4-sulfate were required with an IC50 of 2000 to 5000 μg/mL, whereas chondroitin 6-sulfate was essentially inactive. The antagonistic effect of heparin on hIL-10 activity was shown to be dependent on N-sulfation, inasmuch as de-N-sulfated heparin had little or no inhibitory effect on the IL-10– induced expression of CD16, whereas the effect of de-O-sulfated heparin was comparable to that of unmodified heparin. Furthermore, the inhibition of cell-bound proteoglycan sulfation reduced the hIL-10–mediated expression of CD16 molecules on monocytes/macrophages. Taken together, these findings support the hypothesis that soluble and cell-surface GAG and, in particular, their sulfate groups are important in binding and modulation of hIL-10 activity.

Heparin and heparan sulfate bind interleukin-10 and modulate its activity

Glycosaminoglycans (GAG) are a group of negatively charged molecules that have been shown to bind and directly regulate the bioactivity of growth factors and cytokines such as basic fibroblast growth factor, transforming growth factor-β, IL-7, and interferon-γ. The ability of GAG to interact with human IL-10 (hIL-10) and the effect of these interactions on its biologic activity were analyzed. It was demonstrated by affinity chromatography that hIL-10 binds strongly to heparin–agarose at physiological pH. Biosensor-based binding kinetic analysis indicated an equilibrium dissociation constant, Kd, of 54 nmol/L for this interaction. Human IL-10 stimulated CD16 and CD64 expression on the monocyte/macrophage population within peripheral blood mononuclear cells, with optimal concentrations between 1 and 10 ng/mL. Soluble heparin, heparan sulfate, chondroitin sulfate, and dermatan sulfate were shown to inhibit the hIL-10–induced expression of CD16 and CD64 in a concentration-dependent manner. Heparin and heparan sulfate were most effective with IC50 values of 100 to 500 μg/mL. Considerably higher concentrations of dermatan sulfate and chondroitin 4-sulfate were required with an IC50 of 2000 to 5000 μg/mL, whereas chondroitin 6-sulfate was essentially inactive. The antagonistic effect of heparin on hIL-10 activity was shown to be dependent on N-sulfation, inasmuch as de-N-sulfated heparin had little or no inhibitory effect on the IL-10– induced expression of CD16, whereas the effect of de-O-sulfated heparin was comparable to that of unmodified heparin. Furthermore, the inhibition of cell-bound proteoglycan sulfation reduced the hIL-10–mediated expression of CD16 molecules on monocytes/macrophages. Taken together, these findings support the hypothesis that soluble and cell-surface GAG and, in particular, their sulfate groups are important in binding and modulation of hIL-10 activity.

Macrophages from inflamed but not normal glomeruli are unresponsive to anti-inflammatory cytokines

This study examined the properties and responsiveness to cytokines of macrophages purified from normal and nephritic glomeruli to ascertain whether macrophages activated in vivo develop programmed unresponsiveness to cytokines as do bone marrow-derived macrophages in vitro when activated by interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), interleukin-4 (IL-4), or transforming growth factor-beta (TGF-beta). Macrophages from normal glomeruli did not generate nitric oxide (NO) spontaneously but only after treatment with IFN-gamma and TNF-alpha. NO generation by these macrophages was abrogated by administering IL-4, TGF-beta, or TNF-alpha before but not after IFN-gamma treatment. Glomerular macrophages also expressed beta-glucuronidase, which was increased by TGF-beta and decreased by IFN-gamma and TNF. By contrast, glomerular macrophages from rats with nephrotoxic nephritis did not express beta-glucuronidase even after exposure to TGF-beta. Furthermore, they generated NO spontaneously, and this spontaneous generation of NO was not suppressed by IL-4, TGF-beta, or TNF-alpha. Systemic treatment of nephritic rats with IL-4 reduced NO generation by 40% but did not prevent activation, which is similar to the effect of IL-4 on bone marrow-derived macrophages in vitro when given simultaneously with IFN-gamma. We conclude that macrophages infiltrating inflamed glomeruli have developed programmed unresponsiveness to activating cytokines. This may enable them to function appropriately in the complex conditions within an inflammatory focus.

Interleukin-10 (IL-10) augments allograft arterial disease: paradoxical effects of IL-10 in vivo

Interleukin-10 (IL-10) is an anti-inflammatory helper T cell type 2 (Th2) cytokine that modulates Th1-type cytokine production. Graft arterial disease (GAD) is a vascular obliterative process mediated via the Th1 cytokine interferon-gamma (IFN-gamma); allografts in IFN-gamma-deficient animals do not develop GAD. We investigated the effect of IL-10 and anti-IL-10 on GAD in murine heart transplants and whether anti-IL-10 reestablishes GAD in IFN-gamma-deficient hosts. Major histocompatibility complex class II-mismatched hearts were transplanted for 8 weeks into wild-type or IFN-gamma-deficient mice. In one set of experiments, wild-type hosts received daily administration of phosphate-buffered saline (PBS) or increasing IL-10; in a subsequent set of experiments, wild-type hosts received weekly PBS, rat IgG, or anti-IL-10 monoclonal antibody; IFN-gamma-deficient recipients received weekly PBS or anti-IL-10 monoclonal antibody. Explanted allografts were assessed for parenchymal rejection and GAD, cytokine profiles, and adhesion/costimulatory-molecule expression. Exogenous IL-10 resulted in increased Th2-like cytokine production; nevertheless, it exacerbated parenchymal rejection and GAD and increased CD8(+) infiltration. Anti-IL-10 did not significantly affect the extent of rejection or GAD, cytokine profiles, or immunohistology of the allografts in wild-type hosts. Adhesion molecule (CD54 and CD106) expression was not diminished by IL-10 treatment, and costimulatory-molecule (CD80 and CD86) expression was augmented by administration of exogenous IL-10. Allografts in IFN-gamma-deficient recipients showed mild rejection and no GAD, regardless of anti-IL-10 treatment. IL-10 in vivo thus has markedly different effects than predicted from in vitro experience. Although allografts develop Th2-like cytokine profiles treatment with IL-10 causes exacerbated rejection and GAD.

Role of FcgammaRI (CD64) in erythrocyte elimination and its up-regulation in thalassaemia

To examine any role of the high affinity Fcgamma class I receptor (FcgammaRI) (CD64) in erythrocyte elimination by mononuclear phagocytes (MP) in thalassaemia (thal), we investigated the in vitro interaction of beta-thalassaemic erythrocytes with monocytes (Mo) whose FcgammaR expression had been modulated by cytokines. Treatment of Mo with interferon (IFN)-gamma or interleukin (IL)-10 which up-regulate FcgammaRI, caused a dose-dependent increase in binding of beta-thalassaemic erythrocytes, whereas stimulation with IL-4 which down-regulates the receptor, reduced this interaction, in a dose-dependent manner, to that of normal erythrocytes. Binding of thalassaemic erythrocytes by IFN-gamma or IL-10-treated Mo was inhibited by FcgammaRI-specific reagents. In addition, Mo expression of FcgammaRI and HLA class II DR was determined by flow cytometry in Thai patients with HbH disease (alpha1/alpha2 or alpha1/Hb Constant Spring) (n = 15) or beta degrees -thal/HbE (n = 16). In both groups of patients FcgammaRI expression was increased as compared to normal controls (n = 14): mean fluorescence intensity (+/-SD) 124.79 +/- 38. 77 in HbH disease and 121.86 +/- 18.23 in beta degrees -thal/HbE versus 91.94 +/- 17.36 in normal controls (P < 0.01 and P < 0.001, respectively). In contrast, HLA class II DR expression was similar in patients and controls. The results suggest that, in thalassaemia, up-regulated FcgammaRI on mononuclear phagocytes plays a role in their interaction with erythrocytes and that this process can be modified by cytokines.

MHC class I molecules on CD4 T cells regulate receptor-mediated activation signals

Three T cell populations can be distinguished based on their response to antigen receptor engagement. A sizable fraction dies within hours of TCR ligation, a smaller fraction enters the mitotic cycle, and the remaining T cells merely upregulate the expression of certain cell surface markers. An MHC-I-controlled regulatory mechanism has been identified. MHC I MAbs, or Fab fragments, prevent T cells from mounting a proliferative mitogen response but do not inhibit the mitogen-induced deletion of T cells. IFN-gamma enlarges the fraction of T cells which proliferate in response to mitogen stimulation but, in the presence of MHC I MAb, these cells fail to clonally expand and enter the deletion pathway. Phenotypically, MHC I MAb Fab fragments induce T cells to upregulate the expression of the apoptosis marker CD95, even in the absence of TCR ligand, and prevent the upregulation of costimulatory CD28 molecule expression.

Experimental Murine Trypanosoma congolense Infections. II. Role of Splenic Adherent CD3+ Thy1.2+ TCR-αβ− γδ− CD4+8− and CD3+ Thy1.2+ TCR-αβ− γδ− CD4−8− Cells in the Production of IL-4, IL-10, and IFN-γ and in Trypanosome-Elicited Immunosuppression

Trypanosome-induced suppression of T and B cell responses to parasite-related and -unrelated Ags is considered a major mechanism of evasion of the host’s immune defenses by the parasite. Reduced T and B cell responses have been attributed to suppressor T cells, suppressor macrophages, or both. We have previously shown that endogenously produced IL-10 and IFN-γ mediate the suppression of T cell responses in Trypanosoma congolense-infected mice. Here, we show for the first time that splenic CD3+ Thy1.2+ αβ− γδ− CD4+8− and CD3+ Thy1.2+ αβ− γδ− CD4−8− cells that copurify with plastic-, nylon wool-, or Sephadex G-10-adherent cell populations, in synergy with adherent Thy1.2− cells, are the major producers of IL-4, IL-10, and IFN-γ in T. congolense-infected mice. We further demonstrate the involvement of these cells in the suppression of T cell proliferative responses to mitogen and in B cell responses to a parasite-unrelated Ag.

Elevated major histocompatibility complex class I expression protects T cells from antibody- and macrophage-mediated deletion

Macrophages are capable of destroying T cells with which they form cellular conjugates. The deletion can be prevented by the simultaneous transmission of costimulatory signals. We show here that T cells with elevated major histocompatibility complex (MHC) class I expression are resistant against macrophage-mediated cytotoxicity. T cells that express the CD45RO isotype, considered memory T cells, exhibit MHC class I antigen at higher density than naive CD45RA T cells and upregulate MHC class I expression promptly when they form cellular conjugates with macrophages. We confirm previous observations that CD45RA T cells are more susceptible to antibody- and macrophage-mediated deletion than memory CD45RO T cells. When MHC class I molecules are masked by specific monoclonal antibody or antibody Fab fragments, CD45RA T cells and CD45RO T cells exhibit equal susceptibility to macrophage cytotoxicity, demonstrating that the difference between CD45RA and CD45RO T cells in their sensitivity to macrophage cytotoxicity is determined by their MHC I expression. Separation of CD4 T cells from CD8 T cells deprives memory CD4 T cells of their resistance against macrophage cytotoxicity, suggesting that memory T cells' resistance against destruction by macrophages is controlled by regulatory T cells.

Macrophages may activate or destroy T cells with which they form antigen- or coreceptor-mediated cellular conjugates

The formation of antigen- or mitogen-mediated cellular conjugates with T cells enables macrophages to trigger in T cells costimulatory signals and to facilitate T cell clonal expansion and differentiation. The present study describes T cell death as an alternative consequence of T cell interaction with macrophages. Macrophages initiate the deletion of T cells which they target for conjugate formation through CD4 coreceptors. After suboptimal engagement, the TCR mediates a deletion program. Optimal TCR stimulation induces a rescue program which overrides the deletion program induced by suboptimal antigen receptor ligation or by coreceptor engagement. Evidence is presented suggesting that receptor clustering favors the transmission of activation signals, whereas ligation of nonclustered receptors facilitates T cell deletion.