The effect of recombinant interferon-gamma on human monocyte-derived macrophages

Interferon gamma induces actin polymerization, Rac1 activation and down regulates phagocytosis in human monocytic cells

IFNγ is a potent activator and IL-10 a powerful inhibitor of macrophage functions. However, neither all cellular functions are enhanced by IFNγ nor IL-10 inhibits all cellular responses. Thus, FcγRs-mediated phagocytosis in monocyte-derived macrophages (MDM) increases after IL-10 treatment, and decreases after treatment with IFNγ, although both IL-10 and IFNγ up regulate FcγRI expression. In this work we investigated the effect of IFNγ and IL-10 on phagocytic signaling by FcγRs in MDM. Treatment with IFNγ diminished phagocytosis of IgG-opsonized SRBC (IgG-SRBC) while treatment with IL-10 increased it. These opposite effects cannot be attributed to changes in FcγR expression induced by each cytokine. Early biochemical responses mediated by FcγRs were distinctly affected by cytokine treatment. Syk phosphorylation and the rise in [Ca(2+)](i) were higher after IL-10 treatment, whereas IFNγ treatment also increased Syk phosphorylation but had no effect on the rise in [Ca(2+)](i). IFNγ treatment led to increased basal levels of F-actin and this effect correlated with the decrease in phagocytosis of both IgG-SRBC and non-opsonized Escherichia coli. IL-10 did not alter F-actin basal levels, and enhanced the phagocytosis of E. coli and IgG-SRBC. The level of F-actin reached after IFNγ treatment was not further increased after stimulation with IgG-SRBC or CCL5, whereas MDM treated with IL-10 showed a slightly higher response than control cells to CCL5. IFNγ increased Rac1-GTP levels. Inhibition of PI3K with LY294002 prevented IFNγ-mediated actin polymerization. Our data suggest that IFNγ induces a higher basal level of F-actin and activation of Rac1, affecting the response to stimuli that induce cytoskeleton rearrangement such as phagocytic or chemotactic stimuli.

Induction of nitric oxide synthase in bovine mononuclear phagocytes is differentiation stage-dependent

Bovine monocytes and monocyte-derived macrophages (MDM) activated by various means were assessed for induction of inducible nitric oxide synthase (iNOS), using the Griess assay, Northern blotting and reverse transcription/polymerase chain reaction (RT-PCR). Interferon-gamma (IFN-gamma) induced little, if any, iNOS expression and NO production in MDM, although these cells responded to IFN-gamma in other regards. In contrasts, MDM produced copious amounts of NO when stimulated with LPS or Salmonella dublin, and this was paralleled by high steady state levels of iNOS mRNA. Heat-killed Listeria monocytogenes induced more iNOS mRNA and nitrite than IFN-gamma, but much less than L. mono-cytogenes and IFN-gamma combined. Monocytes differed from M phi with respect to iNOS induction and nitrite production in several regards: (i) LPS and S. dublin induced only low levels of iNOS mRNA and nitrite in monocytes, although cells responded to these stimuli in various other ways: (ii) IFN-gamma alone induced in monocytes iNOS mRNA generation and NO formation, although to a low and variable degree; (iii) upon maximal stimulation (e.g. by L. monocytogenes and IFN-gamma combined), monocytes produced much less nitrite than MDM, and mRNA levels were lower. Regulation of macrophage iNOS varies considerably between species. We provide the first evidence in any species that the steady state levels of iNOS mRNA and NO generation in monocytes and macrophages activated by various means depend on the stage of mononuclear phagocyte differentiation.

Effect of gamma interferon on expression of Fc gamma receptors in monocytes of newborn infants and adults

Fc gamma receptors provide an essential link between cellular and humoral immunity, and little is known about their expression in monocytes of newborn infants. We compared baseline and gamma interferon (IFN-gamma)-induced expression of Fc gamma RI and Fc gamma RII protein and Fc gamma RI mRNA in monocytes from healthy, term infants and adults. Fluorescence-activated cell sorter analysis demonstrated that baseline expression of monocyte Fc gamma RI in newborn infants was not significantly different from that in adults, while Fc gamma RII protein expression in monocytes derived from newborns was significantly higher than that for adults (mean channel fluorescence [MCF] for newborns and adults, 5.53 and 4.50, respectively [P = 0.039]). In vitro treatment with recombinant IFN-gamma increased the expression of Fc gamma RI in monocytes of newborns and adults to the same extent (2.4- and 2.2-fold increase in MCF in newborns and adults, respectively, at 42 h). We developed a semiquantitative fluorescence reverse transcriptase PCR which demonstrated a significant increase in mRNA for Fc gamma RI in monocytes of newborns and adults with in vitro IFN-gamma exposure, indicating that IFN-gamma acts by increasing the transcription or transcript stability of Fc gamma RI mRNA. While there was no significant effect of IFN-gamma treatment on Fc gamma RII expression in monocytes from adults, there was a 20% increase in Fc gamma RII in monocytes from newborns (P = 0.009). Monocytes from healthy, term newborns and adults exhibit comparable baseline and IFN-gamma-induced levels of expression of Fc gamma RI and higher baseline and IFN-gamma-induced levels of expression of Fc gamma RII.

Interferon-gamma inhibits liver regeneration by stimulating major histocompatibility complex class II antigen expression by regenerating liver

The effects of interferon-gamma and interleukin-2 on liver regeneration after 70% hepatectomy in rats was studied immunohistologically, with special attention paid to major histocompatibility complex class II antigen expression. Liver regeneration 2 days after partial hepatectomy as assessed on the basis of bromodeoxyuridine labeling index revealed that regeneration was inhibited significantly in rats given a single dose of interleukin-2 or interferon-gamma compared with rats that underwent only partial hepatectomy. Simultaneous administration of interleukin-2 and interferon-gamma inhibited liver regeneration more markedly than administration of either drug. In rats subjected to partial hepatectomy, Kupffer cells around the portal vein expressed slightly more major histocompatibility complex class II antigen than did sham-operated controls. In the group given interferon-gamma, major histocompatibility complex class II antigen expression was markedly increased. Major histocompatibility complex class II antigen expression was greatest in most Kupffer cells of rats given both interleukin-2 and interferon-gamma. These results suggest that interferon-gamma activates (proliferating) Kupffer cells, in turn leading to suppression of liver regeneration. These major histocompatibility complex class II antigen-positive Kupffer cells act as antigen-presenting cells and present hepatocyte as antigen, the so-called abnormal self, to helper and cytotoxic T cells. Both types of T cells, in turn, may suppress hepatocyte proliferation. The various cytokines induced by the activated Kupffer cells and helper T cells seem to form a network with interferon-gamma to regulate liver regeneration.

Enhancement of macrophage candidacidal activity by interferon-gamma. Increased phagocytosis, killing, and calcium signal mediated by a decreased number of mannose receptors

In contrast to its macrophage-activating capacity, IFN-gamma downregulates expression of the macrophage mannose receptor (MMR), which mediates uptake of Candida and other microorganisms. We found that IFN-gamma induced a concentration-dependent increase in the capacity of human monocyte-derived macrophages to ingest and kill both opsonized and unopsonized Candida albicans and to release superoxide anion upon stimulation with Candida. Mannan or mannosylated albumin inhibited this activated uptake of unopsonized Candida, but glucan did not. Addition of mAb to complement receptor (CR) 3 did not inhibit ingestion; macrophages that lacked CR3 (leukocyte adhesion defect) showed normal upregulation of ingestion by IFN-gamma. The increased candidacidal activity of IFN-gamma-activated macrophages was associated with reduced expression of MMR by a mean of 79% and decreased pinocytic uptake of 125I-mannosylated BSA by 73%; K(uptake) of pinocytosis was not changed. Exposure of resident macrophages to unopsonized Candida did not elicit a transient increase in intracellular free Ca2+ ([Ca2+]i); macrophages activated by IFN-gamma expressed a brisk increase in [Ca2+]i on exposure to Candida. These data suggest that macrophage activation by IFN-gamma can enhance resistance to C. albicans infection in spite of downregulation of the MMR, perhaps through enhanced coupling of the MMR to microbicidal functions.

Modulation of the transcriptional rate of Fc gamma receptor mRNA in human mononuclear phagocytes

Human monocytes and macrophages bear three classes of cell surface receptors for the Fc portion of IgG (Fc gamma RI, Fc gamma RII, and Fc gamma RIII). These receptors mediate phagocytosis and other effector functions and are important in the pathophysiology of hematologic disease, inflammation, and host defense. We have previously shown that interferon-gamma (IFN-gamma) and dexamethasone modulate total Fc gamma RII mRNA levels as well as Fc gamma RI and Fc gamma RII protein expression on monocytes and the monocyte-like cell line U937. In this study, we investigated the modulation of Fc gamma RI mRNA. Additionally, we utilized mRNA stability and nuclear run-on assays to study the mechanism of the modulation of Fc gamma receptor transcripts in the monocyte/macrophage cell line U937. In U937 cells, IFN-gamma increased Fc gamma RI mRNA levels 7.5-fold. Treatment with dexamethasone reduced Fc gamma RI mRNA levels to 0.6-fold of baseline and inhibited by 20-60% the increase in mRNA observed after treatment of the U937 cells with IFN-gamma. On monocytes, treatment with IFN-gamma increased monocyte Fc gamma RI mRNA 6.7-fold. Cotreatment of the IFN-gamma-stimulated monocytes with dexamethasone resulted in a 160% further increase in Fc gamma RI expression. Fc gamma RI and Fc gamma RII mRNA half-lives were then determined in U937 cells by incubation with dexamethasone and/or IFN-gamma for 16 hr and then arresting mRNA transcription with actinomycin-D (10 micrograms/ml). The mRNA half-lives in untreated U937 cells were 3.3 +/- 0.3 hr (Fc gamma RI) and 3.1 +/- 0.3 hr (Fc gamma RII). For either Fc gamma RI and Fc gamma RII, the effect of dexamethasone and/or IFN-gamma on mRNA half-life was not significant (P > 0.5). We also performed nuclear run-on experiments with U937 cells which indicated that IFN-gamma increased the transcription of Fc gamma RI 4.2-fold and Fc gamma RII 1.7-fold. Our data suggest that these changes in Fc gamma RI and Fc gamma RII protein are likely due, at least in part, to increases in mRNA levels secondary to alteration in gene transcription.

Recombinant human migration inhibitory factor has adjuvant activity

Recombinant human migration inhibitory factor (MIF), isolated through functional expression cloning in COS-1 cells, up-regulates expression of genes encoding HLA-DR and interleukin 1 beta (IL-1 beta) and elaboration of IL-1 beta by human monocyte-derived macrophages. Administration of soluble bovine serum albumin or human immunodeficiency virus 120-kDa glycoprotein (HIV gp120) to mice in the presence of recombinant MIF together with incomplete Freund's adjuvant induced a strong T-cell proliferative response comparable to that of complete Freund's adjuvant. Recombinant MIF also increased antibody production, especially of IgG1 and IgM, in mice. Taken together, these results indicate that recombinant MIF may be useful as an adjuvant in the development of vaccines.

Suppression by human recombinant gamma interferon of in vitro macrophage nonopsonic and opsonic phagocytosis and killing

Although gamma interferon (IFN-gamma) exerts profound effects on the state of activation of macrophages, its influence on receptor-mediated phagocytosis and killing of extracellular bacteria is poorly understood. Human monocytes cultured in the presence of human recombinant IFN-gamma exhibited an enhanced capacity to produce superoxide anion. Although these cells bound greater numbers of particles via Fc receptors, their capacity to phagocytose by these receptors or to bind or ingest particles via receptors for C3bi, mannose, or unopsonized Pseudomonas aeruginosa was substantially depressed in a dose-dependent fashion (0.1 to 1,000 U of IFN-gamma per ml). Macrophage phagocytosis of P. aeruginosa and Staphylococcus aureus opsonized with whole serum or with serum deficient in immunoglobulin or complement was also depressed. Macrophages cultured in the presence of IFN-gamma had a diminished capacity to kill both unopsonized and opsonized P. aeruginosa. We conclude that IFN-gamma inhibits macrophage nonopsonic and opsonic receptor-mediated phagocytosis and killing but enhances oxidative radical generation; its production may exacerbate host tissue damage during chronic infection with extracellular pathogens.

Role of interferon-gamma on the in vivo expression of functional interleukin-2 receptors by murine macrophages

Interferon-gamma activates both in vitro and in vivo macrophage functions. Injection of rat recombinant interferon-gamma (rR-IFN-gamma) induced the expression of interleukin-2 receptors (IL-2R) by peritoneal macrophages from normal BALB/c and MRL-+/+ mice. Moreover, rR-IFN-gamma stimulated in a dose-dependent manner the oxidative burst of cells as revealed by luminol-dependent chemiluminescene (LDCL). Resident peritoneal macrophages from MRL-lpr/lpr (mice that develop a systemic lupus-like syndrome) showed a higher PMA-triggered LDCL response. This enhanced activity was accompanied by an increase in IL-2R expression (30% vs. less than 1%). The "activated" macrophages from rR-IFN-gamma-treated normal mice as well as MRL-lpr/lpr mice did not respond to the addition of recombinant interleukin-2 (rHu-IL-2) by an increase in LDCL. However, rHu-IL-2 triggering became efficient when cells enriched in IL-2R-bearing macrophages were preincubated overnight with rHu-IL-2R. This response may point out a functional role for IL-2R and provide a role for IL-2 in certain macrophage functions.

Augmentation of the human monocyte/macrophage chemiluminescence response during short-term exposure to interferon-gamma and tumour necrosis factor-alpha

The effects of short-term (30 min) pre-incubation of human monocytes and macrophages (3-day cultured monocytes) with leucocyte-derived human interferon-gamma (IFN-gamma) and recombinant human tumour necrosis factor-alpha (rTNF-alpha) were examined. Pre-incubation of either monocytes or macrophages with rTNF-alpha or IFN-gamma (100 U/5 x 10(5) cells) augmented their respiratory burst to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), measured by the luminol- and lucigenin-dependent chemiluminescence assay. In addition, both cell types showed a burst of respiratory activity in the presence of rTNF-alpha or IFN-gamma only. The effects of IFN-gamma were removed by adsorption with an anti-IFN-gamma monoclonal antibody and those of rTNF-alpha were abolished by heating at 100 degrees C, or by the addition of anti-TNF-alpha monoclonal antibody. The results demonstrate that both IFN-gamma and rTNF-alpha are stimulators of monocytes and macrophages, and rapidly alter the capacity of the cells to respond to fMLP, which binds to cell surface receptors.

Modulation of human mononuclear phagocyte Fc gamma RII mRNA and protein

Human monocytes and macrophages express three different classes of cell surface receptors for the Fc portion of IgG, Fc gamma RI (CD64), Gc gamma RII (CD32), and Fc gamma RIII (CD16). We utilized a cDNA probe for Fc gamma RII to examine the modulation of Fc gamma RII mRNA by dexamethasone, a synthetic glucocorticoid, and interferon-gamma. We also determined the changes in the expression of both Fc gamma RI and Fc gamma RII protein following treatment with these agents by flow cytometry. In studies performed with the monocyte-like cell line. U937, Northern blot analysis revealed that cells treated with interferon-gamma showed a 2.5-fold increase in Fc gamma RII mRNA levels that was maximal at 14 hr and declined to 1.4-fold over baseline by 48 hr of incubation. Treatment of U937 cells with dexamethasone did not significantly change the level of Fc gamma RII transcripts, but was able to inhibit by up to 50% the increase seen following interferon-gamma treatment. The expression of Fc gamma RII protein on U937 cells was increased 56-72% after 16-24 hr of interferon-gamma treatment, but was only 18% over baseline after 48 hr of incubation. Treatment with dexamethasone caused a small, but significant, decrease in Fc gamma RII protein, and inhibited by 20-60% the induction of Fc gamma RII by interferon-gamma. The modulation by dexamethasone and interferon-gamma of Fc gamma RI protein expression on U937 cells was markedly different from that of Fc gamma RII in both magnitude and kinetics. Interferon-gamma treatment increased Fc gamma RI expression by 240% at 16 hr, and Fc gamma RI remained elevated through 48 hr. Treatment with dexamethasone decreased Fc gamma RI expression by 39%, and also inhibited by 40% the increase induced by interferon-gamma. In contrast to the findings with U937 cells, dexamethasone and/or interferon-gamma treatment had no significant effect on Fc gamma RII mRNA levels or protein expression in monocytes. However, interferon-gamma treatment increased Fc gamma RI expression on monocytes, and this increase was further augmented by treatment with dexamethasone. These data indicate that the modulation of Fc gamma RII on U937 cells is at least in part due to changes in steady state levels of Fc gamma RII mRNA. The difference between the magnitude of the changes in Fc gamma RII mRNA and protein suggests that some translational or post-translational control is involved in regulating the expression of Fc gamma RII.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of macrophages by recombinant interferon-gamma has no effect on myelin phagocytosis but hinders invasion of nerves in organ culture

Myelin phagocytosis in nerves undergoing Wallerian degeneration was shown to depend on their invasion by non-resident, hematogenous macrophages. This process can be studied in vitro using organ cultures of peripheral nerves exposed to cultured peritoneal macrophages. The present report concerns the effect of recombinant interferon-gamma (rIFN-gamma) on luminol-dependent chemiluminescence, macrophage migration and myelin phagocytosis in organ cultures. Chemiluminescence was activated by rIFN-gamma compared to untreated cells. The macrophage population was capable of activation at any phase of exposure to organ cultures. The engagement of macrophages in myelin phagocytosis, however, varied with the timing of the application of rIFN-gamma. Application from the start of the experiment led to activation of chemiluminescence and also to a complete inhibition of macrophage invasion of the organ culture, thus preventing myelin removal. Application of rIFN-gamma at a later phase of the experiment had no effect on cell invasion and also no detectable effect on the efficiency of myelin phagocytosis. There was no indication that myelin phagocytosis by itself activated chemiluminescence in untreated cultures. Phagocytosis of myelin appears to be a function of macrophages independent of activation causing production of oxygen radicals.

Gamma-interferon-induced monocyte major histocompatibility complex class II antigen expression individuals with acquired immune deficiency syndrome

Twelve patients with the acquired immune deficiency syndrome (AIDS) and Kaposi's sarcoma were treated with recombinant human gamma-interferon (rIFN-gamma). A rapid, substantial increase in the fraction of HLA-DQ-positive monocytes was noted after treatment with rIFN-gamma. The rIFN-gamma-induced increase in monocyte HLA-DQ was seen throughout the course of treatment, with the percentage of HLA-DQ-positive monocytes dropping slightly following each week's treatment with rIFN-gamma and then rapidly increasing following the next course of treatment. Although the percentage of HLA-DR-positive monocytes was unchanged (HLA-DR was expressed on greater than 80% of monocytes prior to treatment), the density of HLA-DR on monocytes also increased following rIFN-gamma treatment. Following rIFN-gamma treatment, no changes were seen in CD3, CD4, CD8 T cell numbers, in T cell subset ratio (CD4/CD8), in Leu 7 or CD16 (Leu 11) cell number, in spontaneous Ig secretion, in PHA-induced in vitro proliferation, or in NK activity. These results indicate that exposure to rIFN-gamma in vivo led to the increased expression of class II antigens on monocytes in patients with AIDS.

Interferon gamma-treated human macrophages display enhanced cytolysis and generation of reactive oxygen metabolites but reduced ingestion upon Fc receptor triggering

Human monocyte-derived macrophages treated with recombinant IFN-gamma (rIFN-gamma) and control cells were assessed for three distinct effector functions, all mediated by Fc receptors. rIFN-gamma-primed macrophage displayed markedly reduced phagocytosis of IgG antibody-coated erythrocytes. In contrast, antibody-dependent cytotoxicity towards IgG-antibody-coated erythrocytes and IgG-antibody-coated erythrocyte-induced generation of reactive oxygen metabolite production were increased. The decreased phagocytosis was observed microscopically, as well as in a spectrometric and a radiometric phagocytosis assay. Evidence is presented that the observed impairment in phagocytosis is not the result of increased extracellular lysis or intracellular catabolism of IgG-antibody-coated erythrocytes and that it is not observed with particles ingested in an Fc receptor-independent manner. Enhanced production of reactive oxygen metabolites was detected most clearly by measurement of luminol-dependent chemiluminescence. Antibody-dependent cellular cytotoxicity was shown to proceed also under conditions impeding phagocytosis, and rIFN-gamma-treated macrophage exerted enhanced antibody-dependent cellular cytotoxicity under these conditions too. In all three assays, functional alterations were optimally expressed after a treatment with 500 U/ml for 46 hr. Analysis at the single-cell level revealed that the IFN-gamma-induced alterations were expressed by all macrophages and not the property of distinct macrophage subpopulations. This and earlier studies suggest that the modulation of Fc receptor-mediated macrophage effector functions by IFN-gamma is in part a post-receptor-binding event.

Effect of in vivo injection of recombinant human interleukin-2 on peritoneal macrophages from MRL-lpr/lpr mice

Different characteristics of peritoneal macrophages have been studied, to assess the role of macrophages in the pathogenesis of MRL-lpr/lpr mice which develop a lupus-like syndrome. Resident peritoneal macrophages from MRL-lpr/lpr mice (greater than 10 weeks old) displayed characteristics of activation, while thioglycollate-elicited or resident macrophages from normal mice (Balb/c or MRL-+/+) did not. In addition to Ia antigens, macrophages spontaneously expressed Interleukin-2 receptors (IL2-R) whereas resident macrophages from normal mice did not. Injection of recombinant human Interleukin-2 (rHu-IL2) by the i.p. route to normal mice did not modify the cellular composition of the resident peritoneal population. On the contrary, rHu-IL2 treatment of MRL-lpr/lpr mice induced an enhancement in cell number in the peritoneal cavity. At the same time, macrophages harvested from treated MRL-lpr/lpr mice showed enhanced chemiluminescence triggered by phorbol-12-myristate-13-acetate (PMA) whereas peritoneal macrophages from treated normal mice did not. These results indicate that MRL-lpr/lpr peritoneal macrophages display features of selective 'activation' and suggest that the expression of IL2-R could be involved in the pathogenesis of inflammatory disorders seen in MRL-lpr/lpr autoimmunity.