IL-4 decreases Fc gamma R membrane expression and Fc gamma R-mediated cytotoxic activity of human monocytes

Monocytes can express three classes of FcR for IgG: Fc gamma RI, Fc gamma RII, and Fc gamma RIII (CD64, CD32, and CD16, respectively) of which the Fc gamma RIII is expressed after prolonged culture. Fc gamma R expression is regulated by IFN-gamma. Because IFN-gamma and IL-4 have antagonistic effects on the expression of the FcR for IgE on human monocytes, we studied the effect of IL-4 on Fc gamma R expression and function. We show that IL-4 down-regulates Fc gamma RI, Fc gamma RII, and Fc gamma RIII expression of cultured monocytes and inhibits IFN-gamma enhanced Fc gamma RI expression. Exposure of monocytes to IL-4 for 40 h resulted in a dose-dependent decrease of the expression of all three Fc gamma R that persisted throughout the whole culture period (7 days). Anti-IL-4 antibodies completely reversed the IL-4 effect. In addition the impaired Fc gamma R expression correlated directly with reduced Fc gamma R-mediated function because monocytes cultured in the presence of IL-4 have a reduced capacity to lyse human E opsonized with human IgG anti-D or mouse antiglycophorin A antibodies. These observations, together with the previous finding that IL-4 induces Fc epsilon RIIb expression on monocytes, indicate that IL-4 and IFN-gamma may control the Fc gamma R-mediated immune response by differentially regulating Fc gamma R expression.     

Human alpha-fetoprotein (AFP) causes a selective down regulation of monocyte MHC class II molecules without altering other induced or noninduced monocyte markers or functions in monocytoid cell lines.

Human alpha-fetoprotein (AFP) purified from human amniotic fluid was investigated for its effect on human monocytoid cell lines, including U 937 cells with established subclones. The impact of AFP on the expression of surface markers (MHC class I and II, CD4, CD18, CD45, Fc receptors for IgG) was analyzed using known inducers of monocyte-macrophage differentiation such as phorbol esters and IFN-gamma. Furthermore we investigated the effect of AFP on the induction of macrophage antibody-dependent cell-mediated cytolytic activity (ADCC). AFP did selectively induce a rapid down regulation of surface MHC class II expression. No evidence of alterations was found in the endogenous or differentiation-induced expression of other markers on the surface on monocytes, nor did AFP affect the functional maturation of surface Fc receptors or the ability to express ADCC.     

Regulation of aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23) expression by IL-4 depends on the stage of maturation of monocytes/macrophages.

IL-4 has multiple biologic activities and it has been shown to have effects on B and T lymphocytes, mast cells, NK cells, and monocytes. We studied the influence of IL-4 on the expression of cell membrane determinants, in particular aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23), on human peripheral blood monocytes. We compared the response of monocytes with the response of human alveolar macrophages and monocytic cell lines (U937 and THP1), as mature and more immature representatives of the mononuclear phagocyte system, respectively. A dose-dependent increase of the expression of CD13 Ag was observed when monocytes were cultured with IL-4. Kinetic analyses revealed that this induction was maximal after 2 to 3 days of culture and resembled the kinetics of IL-4-induced expression of Fc epsilon RIIb on monocytes. This IL-4-induced increase was absent when monocytes were cultured with IL-4 and an anti-IL-4 antiserum. Concomitantly, an IL-4-induced increase in leucine-aminopeptidase activity could be observed. Northern blot analysis showed that incubation of monocytes with IL-4 induced a marked increase in CD13 mRNA. Alveolar macrophages also exhibited an increase in CD13 Ag expression when exposed to IL-4. Surprisingly, IL-4 was unable to induce expression of Fc epsilon RIIb on alveolar macrophages. U937 and THP1 cells did not show an induction of CD13 Ag when cultured in the presence of IL-4. However, IL-4 did induce the expression of Fc epsilon RIIb on both cell lines, suggesting the presence of functional IL-4R. Our data demonstrate that IL-4 increases the expression of CD13 Ag on monocytes. This IL-4-induced increase can also be observed in more mature monocytic cells such as alveolar macrophages, but is absent in immature cells such as U937 or THP1 cells. This is functionally accompanied by an increase in leucine-aminopeptidase activity and may be part of the general activation of monocytes/macrophages by IL-4. In conclusion, the data suggest that IL-4 responsiveness, in particular the induction of CD13 Ag and Fc epsilon RIIb expression, may be dependent on the stage of maturation of monocytes/macrophages.     

Influence of recombinant IL-4, IFN-alpha, and IFN-gamma on the production of human IgE-binding factor (soluble CD23)

This study documents the influence of rIL-4, IFN-gamma, and IFN-alpha on the production of IgE-BF and the expression of lymphocyte receptor for IgE or CD23 Ag (Fc epsilon R II) by human mononuclear cells. IL-4 increases the secretion of IgE-binding factor (BF) by highly purified B lymphocytes, adherent cells, and U937 monoblastic cells. The effect of IL-4 on purified B cells is augmented by costimulating the cells with F(ab')2 anti-IgM. IFN-gamma, IL-2, IL-1-alpha, or IL-1 beta and the low m.w. B cell growth factor have no effect on IgE-BF production by purified B cells even when they are used in combination with anti-IgM. Stimulation of purified T cells with IL-4 or IL-4 plus PMA leads to the production of very small amounts of IgE-BF that might well be derived from the contaminating non-T cells. IFN-gamma increases IgE-BF synthesis by unfractionated PBMC, T cell-depleted PBMC, adherent cells, and U937 cells suggesting that it induces monocytes to release IgE-BF, IFN-gamma suppresses the IL-4-induced Fc epsilon R II expression and IgE-BF production by highly purified B cells but not by PBMC or their T cell-depleted fractions. IFN-alpha inhibits IgE-BF production by IFN-gamma-stimulated PBMC and by IL-4-stimulated cells suggesting that it exerts its effect on B cells and on monocytes. Moreover IFN-alpha suppresses the IL-4-induced expression of Fc epsilon R II on B cells. Both IFN-alpha and IFN-gamma suppress the synthesis of IgE by PBMC in response to IL-4. Taken collectively the results indicate that: 1) IL-4 induces IgE-BF production by both B cells and monocytes, 2) IFN-gamma stimulates IgE-BF synthesis by monocytes but suppresses its production by IL-4-stimulated B cells, and finally 3) IFN-alpha inhibits IgE-BF synthesis in response to either IFN-gamma or IL-4.     

IFN-gamma and IL-10 mediate parasite-specific immune responses of cord blood cells induced by pregnancy-associated Plasmodium falciparum malaria

Available evidence suggests that immune cells from neonates born to mothers with placental Plasmodium falciparum (Pf) infection are sensitized to parasite Ag in utero but have reduced ability to generate protective Th1 responses. In this study, we detected Pf Ag-specific IFN-gamma(+) T cells in cord blood from human neonates whose mothers had received treatment for malaria or who had active placental Pf infection at delivery, with responses being significantly reduced in the latter group. Active placental malaria at delivery was also associated with reduced expression of monocyte MHC class I and II in vivo and following short term in vitro coculture with Pf Ag compared with levels seen in neonates whose mothers had received treatment during pregnancy. Given that APC activation and Th1 responses are driven in part by IFN-gamma and down-regulated by IL-10, we examined the role of these cytokines in modulating the Pf Ag-specific immune responses in cord blood samples. Exogenous recombinant human IFN-gamma and neutralizing anti-human IL-10 enhanced T cell IFN-gamma production, whereas recombinant human IFN-gamma also restored MHC class I and II expression on monocytes from cord blood mononuclear cells cocultured with Pf Ag. Accordingly, active placental malaria at delivery was associated with increased frequencies of Pf Ag-specific IL-10(+)CD4(+) T cells in cord blood mononuclear cell cultures from these neonates. Generation and maintenance of IL-10(+) T cells in utero may thus contribute to suppression of APC function and Pf Ag-induced Th1 responses in newborns born to mothers with placental malaria at delivery, which may increase susceptibility to infection later in life.     

Evaluation of the antibody-dependent cytotoxic capabilities of individual human monocytes. Role of Fc gamma RI and Fc gamma RII and the effects of cytokines at the single cell level.

In this report we present evidence that not all human peripheral blood monocytes mediate antibody-dependent cellular cytotoxicity (ADCC), and that this function may be determined on an individual cell by both the type and level of expression of FcR, and by the state of cellular activation and/or differentiation. Although the diverse range of effector and regulatory functions performed by human monocytes suggests the possibility of distinct subsets, it is not clear whether observed functional heterogeneity reflects the presence of true monocyte subpopulations, or whether this diversity represents a continuum of maturational states present in the peripheral circulation. In an attempt to address this question, we investigated the ability of human monocytes to carry out ADCC at the single cell level, with emphasis on the role of the three FcR for IgG (Fc gamma RI, Fc gamma RII, and Fc gamma RIII) in mediating cytotoxicity. Using a modified plaque assay, 58.3% +/- 4.9 of freshly isolated monocytes mediated ADCC, as evidenced by the formation of lytic plaques in monolayers of ox erythrocyte (oxE) target cells. Significant increases in the number of plaque-forming cells were observed after positive selection by flow microfluorimetry for those monocytes expressing high levels of Fc gamma RI and Rc gamma RII, but not Fc gamma RIII. Bispecific antibodies composed of Fab fragments of anti-oxE antibody covalently coupled to Fab fragments of anti-Fc gamma R antibodies were used to independently evaluate the ability of Fc gamma RI, Fc gamma RII, and Fc gamma RIII to mediate single cell cytotoxicity. Significant increases in the number of plaque-forming cells were observed in the presence of anti-Fc gamma RI x anti-oxE and anti-Fc gamma RII x anti-oxE bispecific antibodies, confirming the efficiency of Fc gamma RI and Fc gamma RII as cytotoxic trigger molecules on human monocytes. Incubation of monocytes with purified rIFN-gamma and granulocyte macrophage-CSF, but not IL-2, IL-3, IL-4, IL-6, or TNF-alpha, also resulted in significant increases in the number of monocytes mediating cytotoxicity, suggesting that cytotoxic ability at the single cell level may be influenced by factors which effect monocyte activation and differentiation, respectively. Overall, these studies demonstrate that freshly isolated human monocytes are heterogeneous in their ability to mediate ADCC, and suggest that this functional diversity arises not from discrete subpopulations of cells, but from a continuum of maturational/activational states present within the peripheral circulation.     

IL-1, IL-4, and IFN-gamma differentially regulate cytokine production and cell surface molecule expression in cultured human thymic epithelial cells.

We investigated the response of purified and cloned human thymic epithelial cells (TEC) to IL-1, IL-4, and IFN-gamma stimulation in vitro. IL-1 alpha strongly up-regulated the production of granulocyte-macrophage CSF (GM-CSF), granulocyte CSF (G-CSF), IL-6, and IL-8, as measured by specific immunoenzymetric assays and by increased steady state mRNA levels. IL-4 or IFN-gamma did not induce these cytokines in TEC but in a sustained and dose-dependent manner down-regulated the IL-1-induced GM-CSF protein and mRNA levels. Only IFN-gamma, and not IL-4, suppressed the IL-1-induced G-CSF and IL-8 production, as shown at both the protein and mRNA levels. The inhibition was dose dependent, sustained for at least 96 h, and more pronounced for G-CSF than for IL-8. In contrast, both IL-4 and IFN-gamma enhanced the IL-1-induced IL-6 production. IL-4 and IFN-gamma had additive effects to increase IL-6 secretion and to more completely suppress the IL-1-induced GM-CSF. Analyses of cell surface molecules showed that intercellular adhesion molecule 1 (ICAM-1) expression on TEC was increased by IL-1 or IFN-gamma. IL-4 slightly down-regulated constitutive ICAM-1 levels but did not significantly modify the levels of expression induced by either IL-1 or IFN-gamma. MHC class II expression was induced by IFN-gamma but not by IL-1 or IL-4. The combination of IL-1 and IL-4 with IFN-gamma did not alter the levels of class II MHC Ag induced by IFN-gamma. In conclusion, TEC cytokine production and cell surface molecule expression are differentially regulated via a complex cytokine network. Our data suggest that developing T cells provide, in part, the signals controlling the function of their supporting stroma.     

IFN-alpha and IFN-gamma have different regulatory effects on IL-4-induced membrane expression of Fc epsilon RIIb and release of soluble Fc epsilon RIIb by human monocytes

We used highly purified human monocytes to study the regulation of cell surface and secretion of the low affinity FcR for IgE (Fc epsilon RIIb). IL-4 induces Fc epsilon RIIb expression and soluble Fc epsilon RIIb release in a dose-dependent manner. Significant levels of Fc epsilon RIIb expression were obtained after 12 h of incubation with IL-4 and maximal expression was observed between 24 to 48 h after which the expression declined. Surface expression was followed by secretion of soluble Fc epsilon RIIb which reached maximal levels after 3 to 4 days of incubation and which remained constant throughout 7 days of culture. Induction of Fc epsilon RIIb expression by IL-4 was completely blocked by anti-IL-4 antibodies. Furthermore, IL-1 alpha, IL-2, IL-5, granulocyte-macrophage-CSF, IFN-alpha, IFN-gamma, low m.w. BCGF and also LPS all failed to induce Fc epsilon RIIb expression, demonstrating the specificity of the induction. Fc epsilon RIIb membrane expression induced by IL-4 was reduced in the presence of IFN-gamma and IFN-alpha. Strong inhibition of IL-4-induced Fc epsilon RIIb expression was observed at IFN-alpha concentrations of 450 U/ml (80%), and 100 U/ml of IFN-gamma reduced IL-4-induced Fc epsilon RIIb expression by 70%. Interestingly, soluble Fc epsilon RIIb release was strongly inhibited by IFN-alpha. In contrast, IFN-gamma did not affect soluble Fc epsilon RIIb release, suggesting that reduced membrane expression of Fc epsilon RIIb observed in the presence of IFN-gamma does not reflect inhibition of Fc epsilon RIIb expression but may represent enhanced cleavage or reduced anchoring in the membrane of Fc epsilon RIIb. Finally, IL-5 that has been shown to enhance IL-4-induced Fc epsilon RII on B cells does not enhance significantly IL-4-induced Fc epsilon RIIb membrane expression or subsequent soluble Fc epsilon RIIb release by monocytes. Taken together these results show that IFN-alpha and IFN-gamma have different regulatory effects on IL-4-induced Fc epsilon RIIb membrane expression and soluble Fc epsilon RIIb release by human monocytes.     

Leukotriene B4 potentiates the expression and release of Fc epsilon RII/CD23, and proliferation and differentiation of human B lymphocytes induced by IL-4

This study documents the influence of leukotriene (LT) B4 on human B lymphocyte responses. Incubation of freshly isolated B lymphocytes with LTB4, but not LTC4, induced a slight but significant, time- and dose-dependent increase in the surface expression of Fc epsilon RII/CD23 and class II MHC Ag and in the release of soluble CD23. These changes were maximal at 10 nM LTB4 after an incubation period of 48 h. When B lymphocytes were preactivated in vitro with Staphylococcus aureus Cowan strain I (SAC), neither LTB4 nor LTC4 was able to promote proliferation and/or IgG and IgM secretion. In contrast, when resting B lymphocytes were stimulated with a suboptimal concentration (3 U/ml) of IL-4, LTB4, but not LTC4, potentiated both the Fc epsilon RII/CD23 and the class II MHC antigen expression, and the release of soluble CD23 in a dose-dependent manner, without affecting the kinetics of these responses. Furthermore, LTB4, but not LTC4, amplified both the proliferative response and the IgG and IgM secretion induced by addition of a suboptimal dose of IL-4 (3 U/ml) to SAC-preactivated B lymphocytes. Again, LTB4 did not modify the kinetics of the proliferative response promoted by IL-4. Although LTB4 potentiated IL-4-induced IgG and IgM secretion from SAC-activated B lymphocytes, no production of IgE was observed. These data indicate that LTB4 could play a regulatory role in the modulation of IL-4-induced signaling in human B lymphocytes.     

Functions of the various IgG Fc receptors in mediating killing of Toxoplasma gondii.

The three types of IgG FcR (Fc gamma RI, Fc gamma RII, Fc gamma RIII) on human leukocytes play an important role in elimination of antibody-coated infectious agents. To further understand the role of the different Fc gamma R in mediating this killing, we examined the ability of human myeloid and lymphoid cells to kill the protozoan Toxoplasma gondii in the presence of antitoxoplasma IgG or bispecific antibodies. Although human myeloid cells (monocytes, macrophages, neutrophils, and eosinophils) all lysed unsensitized T. gondii, killing by these cells was significantly enhanced by opsonization with antitoxoplasma rabbit IgG. Human lymphocytes, however, did not lyse T. gondii unless the parasites were coated with antibody. The role of antibody and Fc gamma R in mediating ADCC of T. gondii was then examined using bispecific antibodies made by chemically cross-linking Fab fragments of antitoxoplasma antibodies to Fab fragments of antibodies specific for human leukocyte surface Ag, including Fc gamma R. Thus, simultaneous binding of these bispecifics to parasites and effector cells allowed an evaluation of killing when T. gondii were targeted to each Ag independently. Bispecifics which targeted T. gondii to Fc gamma RI, II or III enhanced lysis by monocytes. However, similar results were obtained with bispecifics targeting T. gondii to non-Fc gamma R Ag (CD11b or beta 2-microglobulin) on monocytes. Likewise, polymorphonuclear leukocytes mediated significantly more lysis in the presence of bispecifics linking T. gondii to Fc gamma RII, Fc gamma RIII, or the two non-Fc gamma R Ag CD11b and beta 2-microglobulin. Thus, although human myeloid cells did not require antibody-Fc gamma R triggering to kill T. gondii, antibody appeared to enhance lysis by capturing and directing the parasites to the effector cell surface. Human lymphocytes, in contrast, mediated significant lysis of T. gondii only in the presence of bispecifics targeting T. gondii to Fc gamma RIII, indicating a requirement for specific triggering of Fc gamma RIII for killing by large granular lymphocytes. Consequently, using bispecifics to compare targeting to specific Ag, both non-Fc gamma R and Fc gamma R, allowed determination of the role of antibody-Fc gamma R interactions in T. gondii killing. In addition, these studies demonstrate the potential of bispecifics in determining the role of specific Ag in killing of or infection by pathogens.     

Modulation of human polymorphonuclear leukocyte IgG Fc receptors and Fc receptor-mediated functions by IFN-gamma and glucocorticoids

Human polymorphonuclear neutrophils (PMN) normally express two distinct types of IgG Fc gamma R, the 40-kDa Fc gamma R referred to as Fc gamma RII and the low affinity 50- to 70-kDa Fc gamma R designated Fc gamma RIII. A third type of Fc gamma R, the 72-kDa high affinity receptor known as Fc gamma RI, is also detectable on PMN that have been activated by IFN-gamma. Using mAb that discriminate among the three known types of Fc gamma R, we examined the effects of IFN-gamma and glucocorticoids on human PMN Fc gamma R expression. We also studied effects of IFN-gamma and the synthetic glucocorticoid dexamethasone (DEX) on antibody-dependent cytotoxicity (ADCC) of chicken erythrocytes and phagocytosis of IgG-coated ox RBC by human PMN. In 20 donors studied, we found that treatment of PMN with 400 U/ml IFN-gamma induced a 9- to 20-fold increase in the number of Fc gamma RI sites per cell, and DEX inhibited this induction of Fc gamma RI by 39 to 73%. Similarly, DEX significantly reduced the IFN-gamma stimulation of ADCC and phagocytosis. IFN-gamma had no effect on expression of Fc gamma RII or Fc gamma RIII. Fc gamma RI and Fc gamma RII expression was unaltered by 24 h of treatment with DEX alone, but Fc gamma RIII expression was sometimes increased by about 20% on PMN cultured with DEX. Nevertheless, we found a small but significant inhibition of ADCC and phagocytosis by 200 nM DEX. Our results indicate that Fc gamma RI plays a major but not exclusive role in the regulation of ADCC and phagocytosis by IFN-gamma and DEX.     

IL-4 and granulocyte-macrophage colony-stimulating factor selectively increase HLA-DR and HLA-DP antigens but not HLA-DQ antigens on human monocytes

A number of cytokines were tested for their ability to modulate HLA-DR Ag expression on normal human monocytes. IL-4, granulocyte-macrophage (GM)-CSF as well as IFN-gamma were able to increase HLA-DR Ag expression on monocytes. IFN-alpha was also able to augment HLA-DR Ag expression, but to a lesser degree. Macrophage-CSF, granulocyte-CSF, TNF-alpha, TNF-beta, and IL-6 were not able to augment HLA-DR Ag expression. There were distinct patterns in the ability of different cytokines to augment class II histocompatibility Ag expression. IL-4 and GM-CSF selectively increased only HLA-DR and HLA-DP, but did not increase HLA-DQ antigens on monocytes. IFN-gamma, however, was able to augment the expression of HLA-DR, HLA-DP, and HLA-DQ Ag. Combinations of IFN-gamma with either IL-4 or GM-CSF did not show any synergy for the augmentation of any of the class II antigens on monocytes.     

Lymphocyte activation gene-3, a MHC class II ligand expressed on activated T cells, stimulates TNF-alpha and IL-12 production by monocytes and dendritic cells

Lymphocyte activation gene-3 (LAG-3) is an MHC class II ligand structurally and genetically related to CD4. Although its expression is restricted to activated T cells and NK cells, the functions of LAG-3 remain to be elucidated. Here, we report on the expression and function of LAG-3 on proinflammatory bystander T cells that are activated in the absence of TCR engagement. LAG-3 is expressed at high levels on human T cells cocultured with autologous monocytes and IL-2 and synergizes with the low levels of CD40 ligand (CD40L) expressed on these cells to trigger TNF-alpha and IL-12 production by monocytes. Indeed, anti-LAG-3 mAb inhibits both IL-12 and IFN-gamma production in IL-2-stimulated cocultures of T cells and autologous monocytes. Soluble LAG-3Ig fusion protein markedly enhances IL-12 production by monocytes stimulated with infra-optimal concentrations of sCD40L, whereas it directly stimulates monocyte-derived dendritic cells (DC) for the production of TNF-alpha and IL-12, unravelling an enhanced responsiveness to MHC class II engagemenent in DC as compared with activated monocytes. Thus similar to CD40L, LAG-3 may be involved in the proinflammatory activity of cytokine-activated bystander T cells and most importantly it may directly activate DC.     

Synergistic effects of IL-4 and IL-18 on IL-12-dependent IFN-gamma production by dendritic cells

Mouse splenic dendritic cells (DCs) produce IFN-gamma in response to IL-12. In the present study, we analyzed effects of Th1 and Th2 cytokines on IFN-gamma production by DCs. IL-18 produced by DCs and macrophages acts in an autocrine manner and augments IL-12-induced IFN-gamma production by DCs as also observed in T and NK cells. Surprisingly, IL-4, a Th2 cytokine, also acts synergistically with IL-12 on IFN-gamma production by DCs. In addition, IL-4 markedly enhances IFN-gamma production when DCs are stimulated through CD40 or MHC class II. These results indicate that both Th1 and Th2 cytokines act on DCs during T cell-DC interaction upon Ag presentation. p38 mitogen-activated protein kinase is constitutively activated in mature DCs and is required for IFN-gamma production by DCs. IL-18 but not IL-4 or IL-12 further activates the p38 mitogen-activated protein kinase activity, suggesting that IL-4 and IL-18 enhance IFN-gamma production through distinct intracellular signal transduction pathways in DCs.     

IL-10 Acts As a Developmental Switch Guiding Monocyte Differentiation to Macrophages during a Murine Peritoneal Infection

The peritoneal wash of BALB/c or C57BL/6 mice contains two populations of macrophages that differ in their level of expression of MHC class II (MHC II). Although both populations efficiently phagocytose bacteria in vivo, only the MHC II(lo) population is effective at phagocytosing apoptotic cells in vivo and only the MHC II(hi) population is effective at presenting Ag to T cells in vitro. Soon after induction of a peritoneal infection both of these macrophage populations are lost from the peritoneal wash fraction. Blood monocytes then enter the inflamed peritoneum and develop into new peritoneal macrophages. Whether these monocytes develop into MHC II(lo) or into MHC II(hi) macrophages is crucially dependent on the cytokine IL-10, which is transiently elevated in the peritoneal wash during the early phase of infection. Monocytes from CD45.1 animals transferred early in infection when the IL-10 concentration is high into congenic CD45.2 recipients develop into the MHC II(lo) macrophage population. Monocytes transferred later, when the IL-10 concentration has fallen, develop into the MHC II(hi) population. In infected IL-10-deficient animals monocytes fail to develop into the MHC II(lo) population but can be induced to do so by exogenous application of IL-10. Finally, high numbers of wild-type monocytes injected into IL-10R1-deficient animals develop into MHC II(lo) macrophages and were able by a bystander effect to induce the differentiation of the endogenous monocytes to the same fate.     

Lack of specificity in the mechanisms involved in the enhancement of the concanavalin A driven human T lymphocyte stimulation by beta-endorphin: studies on activation marker expression, cell cycle and interleukin release.

We report on the effects of a physiological concentration of Beta-Endorphin (BE) (10(-12)M) on Concanavalin A (ConA) stimulated human peripheral blood T-lymphocytes and monocytes. We evaluated the effect of timing of BE addition to the culture medium on thymidine uptake, the kinetics of expression of activation markers (CD69, CD25 and CD71) on CD4+ and CD8+ lymphocytes, and of class II MHC antigens on CD14+ cells (monocytes), the kinetics of interleukin-1 (IL-1), interleukin-2 (IL-2) and interferon gamma (IFN-gamma) release, and the cell cycle. Data show that BE is able to influence T lymphocyte only when added together with ConA at the beginning of culture, suggesting its major activity is on the early phases of the T cell response. BE did not increase the amount of class II MHC antigens on monocytes and did not preferentially stimulate CD69, CD25 and CD71 antigen expression on either CD4+ or CD8+ lymphocytes. After 24 hours, the relative proportions of CD4+ and CD8+ lymphocyte in S and G2-M phases were not affected by BE, although the opioid did augment the number of cells in the proliferative compartments of the cell cycle, S and G2-M, indicating an actual increase in the number of cells committed to proliferation. BE did not consistently influence the amount of IL-1, IL-2 and IFN-gamma found in the supernatant of ConA stimulated cultures. The mechanism of the enhancing effect on the proliferative response of normal human lymphocytes to ConA by BE, does not seem to be selective for or unique to specific lymphocyte subsets.     

Effect of recombinant IFN-gamma (rIFN-gamma) on the mechanism of human macrophage IgG FcRI-mediated cytotoxicity. rIFN-gamma decreases inhibition by cytophilic human IgG and changes the cytolytic mechanism.

Different classes of receptors for the Fc moiety of IgG (Fc gamma R) have been defined on human monocytes and macrophages: Fc gamma RI, Fc gamma RII, and Fc gamma RIII. All three classes are capable of mediating antibody-dependent cell-mediated cytotoxicity (ADCC). Fc gamma RI, which binds monomeric human IgG (hIgG) with high affinity, was shown an effective cytotoxic trigger molecule on different types of cells. In vitro, the inhibition of Fc gamma RI-mediated ADCC by hIgG is well documented. The low affinity receptor classes, Fc gamma RII and Fc gamma RIII, are not blocked by monomeric hIgG. Because monomeric hIgG is present at high concentrations in plasma and interstitial fluids it has been postulated inhibitory in vivo. We investigated the effect of rIFN-gamma on macrophage Fc gamma RI-mediated ADCC in the presence of low doses hIgG. With human E sensitized with hIgG as target cells, Fc gamma RI was studied selectively. We found that rIFN-gamma enhances both expression and cell surface density of Fc gamma RI on cultured peripheral blood monocytes. Furthermore, this cytokine partially reversed the inhibitory effect of monomeric hIgG on ADCC. More interestingly, we found that the cytolytic mechanism of monocyte-derived macrophages changed completely after prolonged culture with rIFN-gamma. Monocytes cultured for 9 days in control medium mediate predominantly phagocytosis. After long term rIFN-gamma stimulation (9 days), monocyte-derived macrophages almost completely lost the capacity to perform phagocytosis. Interestingly, they became highly efficient in mediating extracellular lysis of human E sensitized with hIgG. Short term rIFN-gamma stimulated monocyte-derived macrophages (for the last 40 h of culture) were found to mediate both phagocytosis and extracellular lysis. Our findings suggest that in vivo rIFN-gamma-stimulated macrophages may be most efficient in Fc gamma RI-mediated cytolysis as a consequence of a changed cytolytic mechanism in combination with enhanced Fc gamma RI density.     

Regulation of macrophage activation by IL-3. I. IL-3 functions as a macrophage-activating factor with unique properties, inducing Ia and lymphocyte function-associated antigen-1 but not cytotoxicity

Here we report that IL-3 (also referred to as multi-CSF because of its colony-stimulating activity on a variety of hemopoietic cell lineages) can function as a macrophage-activating factor (MAF). IL-3 was able to regulate the expression of class II MHC Ag and the cellular interaction molecule lymphocyte function-associated Ag-1 on the surface of murine peritoneal exudate cells. The kinetics of IL-3-induced Ia expression appeared to be distinct from that induced by either IFN-gamma, IL-4, or granulocyte-macrophage-CSF. IL-3 was also distinguished from these factors by the finding that it did not induce macrophage tumoricidal activity. In addition to its inherent MAF activities, IL-3 also showed a marked synergy with low doses of LPS (0.05 to 0.5 ng/ml) as well as IFN-gamma in Ia induction. When lymphocyte function-associated Ag-1 expression was evaluated, the effects of these stimuli appeared to be only additive. Although LPS has been shown to inhibit IFN-gamma-induced Ia expression, in our experiments this property of LPS is manifest only when present at doses greater than or equal to 50 ng/ml. At lower concentrations, LPS potentiated both IL-3- and IFN-gamma-induced class II MHC Ag expression. Data presented here also suggest that the synergistic interactions between low doses of LPS and IL-3 are not mediated by known LPS-inducible cytokines of macrophage origin, because rIL-1, TNF-alpha, or IL-6 did not enhance the response to IL-3. Because IL-3 can also participate in the regulation of IL-1 expression, it appears that IL-3 can function as a MAF which selectively regulates the accessory cell characteristics required for Ag presentation, as opposed to the cytolytic functions of the macrophage.