Mononuclear phagocytes: responders to and producers of interferon

Role of type I interferons during macrophage activation by lipopolysaccharide

Activation of macrophages by bacterial lipopolysaccharide (LPS) is accompanied by the secretion of type I interferons (IFNs) which can act in an autocrine manner. We examined the role of type I IFNs in macrophage responses to LPS using bone marrow-derived macrophages (BMM) from IFNAR1-/- mice, which lack a component of the type I IFN receptor and do not respond to type I IFNs. We found that, unlike wild-type (WT) BMM, LPS-treated IFNAR1-/- cells failed to produce nitric oxide (NO), or express inducible NO synthase (iNOS), indicating that type I IFNs are essential for all LPS-stimulated NO production in BMM. Exogenously added type II IFN (IFNgamma) rescued these responses in LPS-treated IFNAR1-/- BMM. In contrast to effects on NO, type I IFNs negatively regulated respiratory burst activity in LPS-primed BMM. We also found that while type I IFNs mediated the anti-proliferative effects of lower concentrations of LPS, at higher concentrations LPS acted in a type I IFNs-independent manner. Finally, we report that type I IFNs are a survival factor for BMM. Despite this, the ability of LPS to also prevent apoptosis in BMM was independent of type I IFNs. These findings highlight the diverse roles of type I IFNs in mediating LPS-stimulated macrophage responses.

Type I interferons mediate the lipopolysaccharide induction of macrophage cyclin D2

Lipopolysaccharide (LPS) is a powerful macrophage-activating agent and antimitogen. We recently showed that LPS unexpectedly induces cyclin D2 in macrophages. Since LPS stimulates macrophages to produce autocrine-acting cytokines, we examined whether LPS induction of cyclin D2 was mediated by one such type of cytokine, type I interferons (IFN). We report that bone marrow-derived macrophages (BMM) lacking a component of the type I interferon receptor (IFNAR-1) do not express cyclin D2 mRNA or protein in response to LPS stimulation (0.01-1 microg/ml for 7-30 h). Consistent with this result, addition of anti-IFN-alpha/beta neutralizing antibodies reduced levels of LPS-stimulated cyclin D2 in normal BMM. Furthermore, IFN-alpha alone induced cyclin D2 mRNA and protein in normal BMM. Thus, we have identified a new role for type I IFN in macrophages, namely, as essential mediators of LPS-stimulated cyclin D2 expression.

Alpha-1 antichymotrypsin is increased in human alveolar macrophages by phorbol myristate acetate or lipopolysaccharide and released from these activated macrophages by glucocorticoid

Alveolar macrophages were obtained from 23 patients and the effects of phorbol myristate acetate (PMA), lipopolysaccharide (LPS), and dexamethasone (DEX) on the proportion of cells with intracellular alpha-1 antichymotrypsin (ACT), and concentrations of ACT in the culture medium were studied in vitro. The alveolar macrophages were obtained by bronchoalveolar lavage at autopsy or from resected lungs at operation and were cultured in suspension for 3 days in medium containing PMA, LPS, DEX, PMA+DEX, or LPS+DEX. Both PMA and LPS significantly increased the percentage of macrophages with intracellular ACT. Dexamethasone did not increase the number of ACT-positive cells and significantly suppressed the increase induced by PMA or LPS, releasing ACT into the culture medium. The release of ACT from macrophages may contribute to the anti-inflammatory effects of corticoids.

Inhibition of macrophage-induced antigen-specific T lymphocyte proliferation by poly I:C: strain and antigen independence

We have previously demonstrated that IFN-alpha/beta, poly I:C (an inducer of IFN-alpha/beta), and IFN-gamma can inhibit the ability of KLH-pulsed peritoneal macrophages to induce proliferation of syngeneic, KLH immune T lymphocytes in CBA/J mice. In this study, we show that this IFN-induced immunosuppression is not restricted to CBA/J (H-2k) mice but is also seen in BALB/cJ (H-2d) mice. A similar inhibition of proliferation is observed with the KLH-specific T cell hybridoma BDK, 100, which requires KLH-pulsed macrophages for optimum proliferation and IL-2 production. The immunosuppression produced by IFN was also independent of the antigen employed. Inhibition of T lymphocyte proliferation was observed when casein, instead of KLH, was used to immunize T cells and to pulse peritoneal macrophages in vivo. Utilizing KLH and casein, the antigen specificity of the inhibition was demonstrated. Therefore, the inhibition by the IFN-inducer poly I:C of macrophage-induced, antigen-specific T cell proliferation is not limited by H-2 type of the mice or to one antigen.

The immunosuppressive effects of bilirubin

The strong effects of bilirubin on various levels of the immune system are multifactorial. Concerning the mechanisms of these effects, we hypothesize that the primary causes of the described actions of bilirubin are the direct interaction of bilirubin molecules with cell membranes.

Establishment of murine macrophage-like mutant and hybrid cell lines: comparative analysis of the differentiation induced by 1 alpha,25-dihydroxyvitamin D3 and recombinant murine interferon-gamma

The purpose of this study is to establish the monocyte/macrophage-like cell lines which are sensitive to potent systemic and local factors, 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2 VD3) and interferon-gamma (IFN-gamma). We established two variant mouse macrophage-like cell lines, whose responses to 1 alpha,25(OH)2 VD3 and IFN-gamma differed from one another. The AH-sensitive mutant cell line (G3) was induced by allowing P388D1 tolerant to 8-azaguanine. G3 mutant cells were then fused with the 1 alpha,25(OH)2 VD3-stimulated bone marrow cells isolated from DBA/2 mice. After AH selection the hybrid cell line (XC) was established. The G3 mutant cell line and the XC hybrid cell line had macrophage-like characteristics, such as surface antigens, Fc receptor, C3 receptor, and lysosomal enzymes. The treatment of G3 mutant cells with 1 alpha,25(OH)2 VD3 inhibited cell proliferation with morphological changes, and increased acid phosphatase activity, phagocytic activity, and F4/80 antigen expression on the cell surface. In contrast, IFN-gamma inhibited cell proliferation without effect on acid phosphatase activity and phagocytic activity but increased F4/80 antigen expression. In XC hybrid cells, on the other hand, IFN-gamma, but not 1 alpha,25(OH)2 VD3, inhibited cell proliferation with morphological changes but increased phagocytic activity and F4/80 antigen expression. In addition, IFN-gamma, but not 1 alpha,25(OH)2 VD3, dose-dependently increased multinucleated cell formation of both cells. These findings suggest that the G3 mutant cell line with macrophage-like characteristics is 1 alpha,25(OH)2 VD3- and IFN-gamma-sensitive, and that the XC hybrid cell line is, despite its macrophage-like characteristics, only IFN-gamma-sensitive. Therefore, these newly established cell lines will provide useful systems in studying the differentiation of monocyte/macrophage lineage.

Activation of NK cells in subjects exposed to mild hyper- or hypothermic load

The effect of mild hyper- and hypothermic stress on release of selected hormones (somatotropin, noradrenaline, etc.), interferon (IFN), and activity of NK cells in the blood was examined in groups of young males during a 30 min exposure to 39 degrees C and 4 degrees C. A quick release of somatotropin was registered in 44% of examinees in the hyperthermic group, while the persons exposed to 4 degrees C reacted with a release of noradrenaline only. Concurrently, an elevation of NK cell activity was observed both in the subgroup releasing somatotropin after hyperthermic stress and in the group exposed to cold. Since these forms of mild stress did not lead to an appearance of IFN in the serum, the possibility of an NK cell activating effect of somatotropin and/or the adrenal hormones was tested. While the adrenal hormones stimulated the NK cell activity in vitro, no support for a similar role for somatotropin was found.

Recombinant human interferon-gamma induces increased IgE receptor expression on human platelets

Human recombinant interferon-gamma (IFN-gamma) significantly increased the expression of receptors for IgE (Fc epsilon RII) on blood platelets. Fc epsilon RII was measured by specific binding of 125I-labeled IgE or flow cytometry experiments. Scatchard analysis of 125I-labeled IgE binding curves revealed that treatment with IFN-gamma increased the number of Fc epsilon RII but did not change the value of the association constant of Fc epsilon RII for 125I-labeled IgE. IFN-alpha had no effect on the expression or affinity of Fc epsilon RII. In addition to Fc epsilon RII, IFN-gamma also modified the expression of the glycoprotein IIb-IIIa complex on the platelet membrane.

Activation of human monocyte-derived macrophages cultured on Teflon: response to interferon-gamma during terminal maturation in vitro

Macrophages (M phi) are potential antitumor effector cells derived from circulating blood monocytes (mo). Most studies on human mo/M phi biology and function have been performed using immature mo precursor cells. However, the conclusions drawn may be questionable, as mo have to undergo terminal differentiation before they reach relevant tissue sites of inflammation and immune reaction. We have analyzed the ability of mo-derived, teflon-cultured M phi to respond to activating stimuli with an increased tumor cytotoxic effector cell function using recombinant interferon-gamma (IFN-gamma), IFN-alpha 2, granulocyte/macrophage colony stimulating factor (GM-CSF), interleukin(IL) 2, IL 1 alpha, and bacterial lipopolysaccharides (LPS) as mediator molecules. It could be shown that the response of M phi to the most potent activator molecule, IFN-gamma, depends on the terminal differentiation from the mo stage to the mature M phi. Whereas adherent mo could be activated only moderately, M phi increased their cytotoxicity by a factor of up to 400. IFN-gamma activation positively correlated with the effector cell number, the time of incubation and the dosage used. Activation did not depend on the presence of LPS, and was lost within 24 to 48 h. LPS itself activated cells only in the microgram range. IFN-alpha 2 activated M phi only at a two log higher concentration than IFN-gamma; GM-CSF was only slightly effective, whereas M phi incubation with IL 1 alpha or IL 2 did not result in M phi activation. Thus, the ability of human M phi to become activated appears to be a function of cellular maturation and is acquired during the terminal step of M phi differentiation. Teflon-cultured M phi could facilitate studies of the activation of human M phi and may be more suitable cells for adoptive immunotherapy in cancer patients than blood monocytes.

Role of interferon in streptococcal infection in the mouse

In previous studies, we have shown the rapid in vitro induction of IFN gamma from human T cells by highly purified peptic extracts of M proteins from Streptococcus pyogenes. The present report extends these in vitro studies and shows that a mixture of both alpha/beta and gamma IFN were present in spleen cell homogenates after in vivo treatment with M protein wild-type (M+) or mutant (M-) S. pyogenes strains. The levels of bacterial-induced IFN were found to be greater in M+ treated animals. Additional studies in vivo showed that pretreatment of mice with heat-killed M+ S. pyogenes organisms significantly protected mice to pneumococcal infection compared to similarly treated M- or control animals (P less than 0.001). Further, antibodies to mouse IFN alpha/beta and antibodies specific to a synthetic N-terminal peptide of mouse IFN gamma enhanced the death of animals due to pneumococcal infection and blocked the protection observed in animals previously treated with heat-killed M+ organisms. Most importantly, treatment of mice with either type of IFN alone enhanced the survival of mice to levels similar to that observed by treatment with M+ organisms (P less than 0.05). The results strongly suggest that IFN can play a crucial role, directly or indirectly, in controlling infection by Streptococcus pneumoniae and perhaps other streptococci.

The interaction of interferon with the immune response

Interferon (IFN) is a component of the immune response and influences immune responses as demonstrated by in vitro experimentation. In this review these complementary aspects of IFN's interaction with the immune response are discussed. Of chief interest is IFN-gamma ('immune' IFN) but IFNs-alpha and -beta are also considered.

Synergistic interaction of a cytokine produced by embryonic fibroblasts and a lymphokine contained in Con A-stimulated spleen cell culture for murine macrophage differentiation: a model experiment using cell line cells, M1

The modulating activity of the culture supernatant of Con A-stimulated murine spleen cells for macrophages was investigated by using M-1 cells, which could differentiate into macrophage-like cells (referred to as M+1 hereafter), cocultured in a conditioned medium (CM) containing a differentiation factor (DF) obtained from the secondary culture of murine embryonic fibroblasts. DF induced Ia antigens on M-1 cells at a high rate in parallel with the appearance of Fc-receptor (FcR)-dependent phagocytic activity for erythrocytes coated with an antibody (EA). In contrast, Con A-sup alone had no modulating effect on M-1 cells. However, the Con A-sup stimulates synergistically M-1 cells with DF. Thus, coculture of M-1 cells with Con A-sup and DF generates M++1 cells which possess higher phagocytic activity than M+1 cells. These cells also exhibited stronger accessory cell activity than M+1 cells when tested for their promoting effect on IL-2 production by Sephadex G-10-passed spleen cells. The accessory cell activity of M++1 cells was further enhanced by culture with lymphocytes in the presence of indomethacin while that of M+1 cells did not change. These findings suggest that M-1 cells probably acquire potentiating, as well as inhibitory activity at the same time when cultured with DF and Con A-sup. The functional maturation caused by Con A-sup seemed to be associated with the expression of a receptor for a lymphokine, termed phagocytosis-augmenting factor (PAF) which is present in the Con A-sup. Such a receptor appeared to be common to macrophage lineage, since PAF in Con A-sup was absorbed out with splenic adherent cells and peritoneal exudate cells (PEC) in addition to M+1 cells, but not with nonadherent splenic lymphocytes or lymphoid cell line cells, such as EL-4 and L-1210. This fact suggests that PAF is different from interferon-gamma (IFN) which is known to modulate the function of lymphocytes. Inability of PAF to bind Cibacron Blue-Sepharose, unlike IFN, supports this notion. The molecular weight of PAF is approximately 2-3 X 10(4). Thus, the present studies suggest the requirement of at least two signals for the full maturation of macrophages, a cytokine represented by DF and a lymphokine, by PAF.

The effect of bilirubin on the Fc receptor expression and phagocytic activity of mouse peritoneal macrophages

The effect of bilirubin on the phagocytic activity of mouse peritoneal macrophages and on the expression of Fc receptors and receptors for SRBC was studied. Intraperitoneally administered bilirubin influenced the expression of Fc receptors for IgM, IgG2B, IgA and IgE, whereas the expression of other receptors as well as the phagocytic activity of peritoneal macrophages remained unchanged. The possible mechanism of the effect of bilirubin on Fc receptors is discussed.

Differential effects of recombinant human interferon-alpha A/D on expression of three types of Fc receptors on murine macrophages in vivo and in vitro

Recombinant human interferon-alpha A/D (IFN-alpha A/D) is known to act on murine cells. We studied the in vivo and in vitro effects of pure IFN-alpha A/D on the surface expressions of the three types of murine macrophage Fc receptors (FcRI, II, III). Peritoneal macrophages obtained from BALB/c mice injected 24 h previously with IFN-alpha A/D showed increased expressions of FcRI and FcRII, because an enhanced capacity to bind monoclonal IgG2a- or IgG2b-coated sheep red blood cells was revealed. However, an optimal IFN-alpha A/D dose of a distinct narrow range was required to induce the maximum increase in each type of FcR. Furthermore, the antibody-dependent cellular cytotoxicity mediated by either FcRI or FcRII was also increased with the same optimal dose of IFN-alpha A/D. On the other hand, IFN-alpha A/D did not induce any change in the surface expression of FcRIII, which was demonstrated by the binding of monoclonal IgG3-coated sheep red blood cells. The in vitro treatment of peritoneal macrophages with IFN-alpha A/D also increased the FcRI expression. In contrast with in vivo treatment, however, IFN-alpha A/D treatment in vitro did not bring about any change in the FcRII expression. The FcRIII expression also remained unchanged with IFN-alpha A/D in vitro. Lymphokine-rich mouse spleen cell supernatants which contained natural IFN-gamma again enhanced the FcRI expression, but did not modulate the expressions of FcRII or FcRIII in vitro.

Biochemical analysis of mutants of a macrophage cell line resistant to the growth-inhibitory activity of interferon

While a multiplicity of cellular and biochemical effects are mediated by interferons on cultured cells, the mechanisms involved in the direct growth-inhibitory activity of interferons remain problematic. We have previously found that variants in cAMP metabolism in a macrophage cell line, J774.2, were at least 50-fold less sensitive to the growth inhibitory activity of interferons (IFN) than the parental clone. To test the hypothesis that cAMP mediates the growth inhibition produced by IFN in these cells, interferon-resistant variants were selected and characterized with respect to cAMP synthesis and function. Approximately one-third of the IFN-resistant clones were found to be resistant to growth inhibition produced by cholera toxin, but not 8Br-cAMP. IFN was fully able to protect all of the interferon-resistant/choleratoxin-resistant (IFNr/CTr) clones against infection by vesicular stomatitis virus and markedly stimulated 2', 5'-oligodenylate synthetase activity. These IFNr/CTr variants were shown to have a defect in adenylate cyclase. The remaining IFN-resistant clones were fully susceptible to the growth-inhibitory effects of cholera toxin because their basal and stimulated adenylate cyclase activity is similar to that of the parental clone. IFN failed to protect these IFNr/choleratoxin sensitive clones against infection by vesicular stomatitis virus and failed to stimulate 2', 5-oligodenylate synthetase, suggesting that they have defective or deficient IFN receptors. In addition, IFN failed to increase intracellular cAMP levels in both IFNr/CTr and IFNr/choleratoxin sensitive clones. These results provide firm genetic and biochemical evidence that the growth inhibitory effects of IFN on this cell line are mediated by cAMP.

Interferon suppresses pinocytosis but stimulates phagocytosis in mouse peritoneal macrophages: related changes in cytoskeletal organization

Treatment of thioglycolate-elicited macrophages with mouse beta-interferon markedly reduces pinocytosis of horseradish peroxidase and fluorescein isothiocyanate (FITC)-dextran but stimulates phagocytosis of IgG-coated sheep erythrocytes. Experiments with FITC-dextran have revealed that the overall decrease in pinocytosis is due to a nearly complete inhibition of pinocytosis in a large fraction of interferon-treated macrophages. In the remaining cells pinocytosis continues at a rate similar to that in untreated control cells. A considerable reduction in the number of cells pinocytosing FITC-dextran was observed within 12 h from the beginning of interferon treatment. Measurement of the overall level of pinocytic activity with horseradish peroxidase showed a progressive decline through 72 h of treatment. In the interferon-sensitive subpopulation, there were marked changes in cytoskeletal organization. Microtubules and 10-nm filaments were aggregated in the perinuclear region while most of the peripheral cytoplasm became devoid of these cytoskeletal structures as observed by fluorescence and electron microscopy. In addition, interferon treatment of macrophages appeared to disrupt the close topological association between bundles of 10-nm filaments and organelles such as mitochondria, lysosomes, and elements of the Golgi apparatus and endoplasmic reticulum. Such alterations in the distribution of microtubules and 10-nm filaments were not seen in the interferon-insensitive subpopulation. We have investigated the mechanism of the interferon-induced enhancement of phagocytic activity by binding IgG-coated sheep erythrocytes to mouse peritoneal macrophages at 4 degrees C and then initiating a synchronous round of ingestion by warming the cells to 37 degrees C. Thioglycolate-elicited macrophages that had been treated with mouse beta-interferon ingested IgG-coated erythrocytes faster and to a higher level than control cells in a single round of phagocytosis. In interferon-treated cultures, phagocytic cups became evident within 30 s of the shift of cultures from 4 degrees to 37 degrees C, whereas in control cultures, they appeared in 2 min. Cytochalasin D, an inhibitor of actin assembly and polymerization, abolished phagocytic activity in both control and beta-interferon-treated macrophages. However, to inhibit phagocytosis completely in thioglycolate-elicited interferon-treated macrophages, twice as much cytochalasin D was required in the treated as in control cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological and antigenic similarities of murine interferon-gamma and macrophage-activating factor

Murine peritoneal exudate cells (PEC) treated with murine recombinant interferon-gamma (IFN-gamma) (greater than 99% estimated purity), or concanavalin A-stimulated spleen cell supernatants developed tumoricidal properties (macrophage activation factor [MAF] activity). MAF activity was found to occur with treatments of 10 U/ml IFN-gamma, and at levels as low as 1 U/ml IFN-gamma if a second signal (5 ng/ml endotoxin) was present in the MAF assay. Endotoxin (lipopolysaccharide [LPS]) alone at these levels failed to induce MAF; induction of MAF was observed at 1,000-fold greater levels. The ability of IFN-gamma to stimulate murine PEC was species specific. Various sources of materials that displayed MAF activity, including supernatants from interleukin 2-dependent cloned cytotoxic murine T lymphocyte lines that did not display detectable antiviral activity, were neutralized by antibody raised and affinity purified against recombinant IFN-gamma. Thus, IFN-gamma, although never detectable by antiviral assays, appears to be present in many lymphokine preparations and has potent macrophage activation capability.

Induction of human gamma interferon by structurally defined polypeptide fragments of group A streptococcal M protein

The presence of interferon (IFN) has been demonstrated previously (i) in fluids obtained from the middle ears of children with Streptococcus pneumoniae infections, (ii) from the serum of mice injected intraperitoneally with either S. pneumoniae or Streptococcus pyogenes, and (iii) from human lymphoid cell cultures treated with a variety of bacteria. In this study, we showed that highly purified peptic extracts of three different serotypes of group A streptococcal M protein (pep M5, pep M6, and pep M24) stimulated human peripheral leukocytes to produce IFN. IFN production was apparent by 10 h and peaked 24 h after exposure. Dose-response experiments indicated that IFN could be detected in cultures treated with concentrations of M protein as low as 6 micrograms/ml, whereas maximum IFN production occurred at a concentration of 200 micrograms/ml. The IFN had antigenic and physicochemical characteristics of IFN-gamma. Preliminary leukocyte fractionation studies revealed that the IFN-producing cell was a nonadherent lymphocyte with receptors for sheep erythrocytes (T cell). Rabbit antisera specific for these structurally defined polypeptide fragments of streptococcal M protein (pep M5, pep M6, and pep M24) blocked IFN induction by each of the polypeptides. The data suggest that the different serotypes of streptococcal M protein may induce IFN by a common structural determinant shared by each of the polypeptide fragments tested.

Effect of intravenous recombinant alpha-2 interferon on monocyte Fc-dependent phagocytosis in patients with malignant melanoma

Recombinant alpha interferons (IFN-alpha) have diverse effects on the immune response. Alpha IFNs have been shown to increase the number of monocyte Fc receptors and Fc dependent phagocytosis in vitro. Therefore, we prospectively evaluated Fc-dependent phagocytic activity in a group of 14 patients with Stage III melanoma receiving from 10 to 100 X 10(6) u of recombinant DNA-produced alpha-2 interferon (IFN-alpha 2) five days a week for four weeks. Monocyte Fc-dependent phagocytosis (FcDP) was assayed by measuring the ingestion of 51Cr-labeled, IgG-coated sheep erythrocytes before, and on Days 2, 5, and 19 of IFN therapy. Each patient was simultaneously compared with the same unmatched normal controls during the assay period. Monocyte FcDP was unchanged in 8/14 patients on each of the three sampling days. Increases in FcDP occurred in 4/14 patients on Day 2 and only 1/14 on Day 19. Recombinant DNA-produced IFN-alpha 2 did not persistently augment monocyte FcDP irrespective of the dose administered. Moreover, there may be untoward effects on monocyte FcDP in vivo from intravenous administration of high dose IFN-alpha 2 since a distinct, but statistically insignificant (p = 0.06) trend of inhibition of FcDP by Day 19 of therapy was observed. Monocyte FcDP activity of normal controls fluctuated from day to day. The intrinsic variability in monocyte FcDP as assessed by this technique may conceal an effect(s) of IFN preparations in vivo. Additional studies are needed to further define the effects of purified IFN preparations on monocyte and tissue-derived macrophage effector functions.

Structure and modulation of Fc and complement receptors

Recent experiments have revealed the structure of some phagocytosis-promoting receptors. The C3b receptor is a single-chain membrane glycoprotein of Mr 205,000, while the C3bi receptor is composed of two surface glycoprotein chains, of Mr 180,000 and 100,000. Fc receptors all appear to be single-chain glycoproteins of approximately Mr 50,000. Despite this structural similarity, Fc receptors display a broad range of heterogeneity with respect to ligand specificity. One type of Fc receptor (Fc gamma 2b/gamma 1R) appears to function as a ligand-dependent ion channel; the ion flux initiated by the ligation of this receptor may represent the proximal signal sent by this Fc receptor. The second signal sent by other Fc receptors and by the C3 receptors is uncharacterized, except for the observation that the second signal generated by C3 receptors is distinct from that of Fc gamma 2b/gamma 1R.

Identification of interferon-gamma as the lymphokine that activates human macrophage oxidative metabolism and antimicrobial activity

Human blood mononuclear leukocytes stimulated with toxoplasma antigen, concanavalin A, mezerein plus lentil lectin, or staphylococcal enterotoxin A secreted a factor (macrophage-activating factor, or MAF) that enhanced the capacity of human macrophages to release H2O2 and to kill toxoplasmas. The same lymphoid supernatants contained IFN gamma but not IFN alpha or IFN beta. The MAF activity of six of seven unfractionated supernatants was completely eliminated by a monoclonal antibody that neutralizes IFN gamma, and MAF in the remaining supernatant was almost completely neutralized. Native IFN gamma partially purified by two independent protocols to specific activities of 1 X 10(6) and 10(7) U/mg protein was enriched in MAF activity at least as much as in antiviral activity. The capacity of macrophages to secrete H2O2 after incubation in partially purified native IFN gamma (mean peak stimulation, 8.8-fold) was greater than with unpurified lymphokines (3.8-fold) and sometimes equaled or exceeded the capacity of freshly harvested monocytes. The MAF activity of the partially purified native IFN gamma preparations was abolished by monoclonal anti-IFN gamma. Finally, IFN gamma of greater than 99% estimated purity was isolated (at Genentech, Inc.) from bacteria transformed with the cloned human gene for this lymphokine. Recombinant IFN gamma had potent MAF activity, stimulating the peroxide-releasing capacity of macrophages an average of 19.8-fold at peak response and enhancing their ability to kill toxoplasmas from 2.6 +/- 1.3% for untreated cells to 54 +/- 0.4% for treated cells. Attainment of 50% of the maximal elevation in peroxide-releasing capacity required a geometric mean concentration of 0.1 antiviral U/ml of recombinant IFN gamma, which is estimated to be approximately 6 picomolar for this preparation. Peroxide secretory capacity and toxoplasmacidal activity of macrophages peaked 2-4 d after exposure to IFN gamma. Peroxide-secretory capacity remained elevated during at least 6 d of continuous exposure, but the effect of IFN gamma was reversed within about 3 d of its removal. Activation was usually but not invariably accompanied by characteristic changes in cell morphology. Thus, IFN gamma activates human macrophage oxidative metabolism and antimicrobial activity, and appeared to be the only factor consistently capable of doing so in the diverse LK preparations tested.

Genetic evidence that action of cAMP-dependent protein kinase is not an obligatory step for antiviral and antiproliferative effects of human interferon in Chinese hamster ovary cells

Several Chinese hamster ovary (CHO) cell mutants with altered cAMP-dependent protein kinases were utilized to study the possible involvement of this enzyme in mediating interferon effects in cultured cells. Human fibroblast interferon had a pronounced protective effect for CHO cells against encephalomyocarditis virus (EMCV). This protective effect was also observed in cAMP-resistant CHO mutants with protein kinase defects, although to a slightly lesser extent. EMCV, however, which grows well in wild-type CHO cells, grew poorly in the cAMP-resistant CHO mutants even in the absence of interferon, suggesting that cAMP-dependent protein kinase is involved in the normal growth of this virus. The growth inhibitory and morphological effects of human fibroblast interferon on CHO cells as well as the induction of 2',5'-oligoA synthetase and the level of RNase F activity (which is constitutive in CHO cells) were very similar in wild-type and mutant CHO cells. It is concluded from these studies that cAMP-dependent protein kinase may have a facilitating role in antiviral activity of interferon, but does not have an obligatory role in mediating either the antiviral or antiproliferative effects of interferon in CHO cells.

An assay of mononuclear cell dynamics in various subcutaneous cranial sites

Although polymorphonuclear leukocyte kinetics at sites of tissue injury have been well documented, analogous mononuclear cell data have yet to be reported because of the lack of suitable assay techniques. In this study, counts of mononuclear cells adherent to nitrocellulose filter discs implanted in four subcutaneous sites for nine consecutive days showed a greater degree of cellular accumulation in the temporalis than in the frontalis region, the data for the masseter and submandibular regions being similar and intermediate. This type of assay may prove useful in elucidating the role of mononuclear cells in wound healing and the effect of antiinflammatory agents on mononuclear cell kinetics.

Genetic analysis of the role of cAMP in mediating effects of interferon

The effects of interferon (IFN) on Fc receptor-mediated phagocytosis, intracellular cAMP levels, antiviral activity, and growth inhibition were analyzed in a cloned macrophage-like cell line, J774.2, and variants derived from it. Purified IFN increased Fc receptor-mediated phagocytosis in J774.2 cells, and in cAMP-responsive nonphagocytic variants but was without effect in cAMP-unresponsive nonphagocytic variants, in adenylate cyclase-deficient variants, and in cAMP-dependent protein kinase-deficient variants. Under conditions in which IFN augmented phagocytosis, it increased intracellular levels of cAMP. Parental cells were highly sensitive to IFN-mediated growth inhibition. In contrast, cAMP-dependent protein kinase-deficient variants were only 1/100th as sensitive to growth inhibition by IFN. All cell lines tested, both responsive and unresponsive to cAMP, were equally protected by IFN against infection with vesicular stomatitis virus, demonstrating that the antiviral state was independent of cAMP. These results indicate that, in transformed macrophages, stimulation of phagocytosis and inhibition of growth by IFN are mediated through intracellular cAMP, whereas the antiviral state induced by IFN is independent of cAMP.