Identification of a T cell hybridoma that produces large quantities of macrophage-activating factor

A murine T cell hybridoma, constructed by fusion of alloantigen- activated T cells with the BW5147 T cell lymphoma, which produces a lymphokine capable of inducing tumoricidal activity in macrophages, has been identified. Lymphokine release could be detected only after mitogen stimulation of the T cell hybridoma culture. Upon cloning of the parental hybridoma, 24 out of 27 clones produced tumoricidal- inducing activity. Seven clones produced more cytocidal-inducing activity than did conventional supernatants, generated by concanavalin A stimulation of normal murine spleen cell cultures, which contained macrophage-activating factor (MAF). The supernatant of hybridoma clone 24/G1 was 25 times more active than conventional MAF preparations. Using supernatants from a variety of clones, the levels of macrophage- activating activity and interleukin 2 were found to vary independently of one another. The lymphokine produced by hybridoma clone 24/G1 appeared to be identical to conventional MAF by a variety of criteria including: (a) a requirement for a second signal for induction of tumoricidal activity in macrophages, (b) inactivation after incubation for 1 h at 65 degrees C, and (c) loss of activity after treatment at pH 4.0 but not at pH 5.0. Like conventional MAF, the hybridoma MAF eluted as a single peak after molecular sieve chromatography on Sephadex G100 and exhibited an apparent molecular weight of 55,000. Although somewhat heterogeneous, the majority of hybridoma 24/G1 MAF displayed an isoelectric point of 5.4 as determined using the chromatofocusing technique. These results thus illustrate the usefulness of T cell hybridomas in distinguishing between various lymphokine activities and indicate that the T cell hybridoma clone 24/G1 will be of particular usefulness in achieving the biochemical purification of substantial quantities of murine MAF.     

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.     

Regulation of murine macrophage Ia antigen expression by a lymphokine with immune interferon activity

A culture supernatant of concanavalin A-activated spleen cells (Con A supernatant) induced murine macrophages to express Ia antigens in vitro. Biochemical characterization of the Con A supernatant indicated that the macrophage Ia antigen regulatory activity shares molecular weight, pI, and hydrophobic and affinity characteristics with immune interferon (IFN-gamma). Antiserum to mouse IFN-gamma neutralized both the macrophage Ia antigen regulatory and IFN-gamma bioactivities of the Con A supernatant. Furthermore, both partially purified murine IFN- gamma (10(7) U/mg protein sp act) and IFN-containing culture supernatants of the murine BFS T cell line-induced macrophage Ia antigen expression in vitro. Culture supernatants containing colony- stimulating factor, interleukin 1, interleukin 2, macrophage migration inhibitory factor, and a macrophage-activating activity that were distinct from IFN-gamma did not induce macrophage Ia antigen expression. Taken together, the data indicate that the in vitro expression of Ia antigens on macrophages is regulated by an activity that has the characteristics of interferon.     

Constitutive production of novel macrophage-activating factor(s) by human T cell hybridomas

Human T cell hybridomas were constructed by somatic cell fusion in order to dissect molecular heterogeneity of human macrophage activating-factors (MAF). Two stable human hybridoma supernatants contained MAF activity capable of inducing human monocytes tumoricidal without the help of bacterial lipopolysaccharide (LPS). These supernatants in the presence of LPS could also render mouse macrophages tumoricidal. In contrast, recombinant and natural human interferon-gamma (Hu-IFN-gamma) activated human monocytes, but not mouse peritoneal macrophages. The supernatants from the two clones could neither support the growth of human-granulocyte-macrophage colony stimulating factor/human-interleukin-4-dependent (Hu-GM-CSF/Hu-IL-4) cell lines, such as AML 193 and TALL-101, nor stimulate the proliferation of human-interleukin-2-dependent human cell line and lectin-stimulated lymphoblast, which are responsive to human-interleukin-2 and human-interleukin-4. Rabbit or murine antibodies against human-interferon-gamma (Hu-IFN), human-granulocyte-macrophage colony stimulating factor, human interleukin-1 alpha, human-interleukin-1 beta, human-interleukin-6, human-tumour necrosis factor (Hu-TNF), human-lymphotoxin and human-macrophage migration inhibitory factor (Hu-MIF) could not absorb MAF activity. MAF activity in the hybridoma supernatants is associated with the two polypeptides of molecular weights of 70,000-80,000 and 20,000-30,000 daltons, as determined by gel filtration. These results indicate decisively that novel MAF molecule(s) is secreted by human T cell hybridomas.     

Expression of macrophage procoagulant activity in murine systemic lupus erythematosus.

To explore the induction of monocyte/macrophage procoagulant activity in autoimmune disease, the BXSB murine model of systemic lupus erythematosus was studied. Splenic macrophage procoagulant activity rose coincident with age and the development of glomerulonephritis from 38 +/- 6 mU/10(6) macrophages at 1 mo to a maximum of 29,000 +/- 15,000 mU at 4 mo. Macrophages from 1-mo-old mice could be induced to express a 1,000-fold increase in monocyte/macrophage procoagulant activity when incubated with lymphocytes or lymphocyte supernatants from 5-mo-old mice. Plasma from 5-mo-old but not from 1-mo-old mice was able to induce the production of the lymphokine by cells from 1-mo-old animals. This lymphokine was not interleukin 1,2, or gamma interferon. We conclude that induction of monocyte/macrophage procoagulant activity parallels disease development in the male BXSB mouse, is dependent on the interaction between lymphocytes and plasma factors, and may be important in mediation of injury in lupus nephritis.     

Interferon γ and lymphotoxin or tumor necrosis factor act synergistically to induce macrophage killing of tumor cells and schistosomula of schistosoma mansoni

Macrophages play a crucial role in the defense against tumors and parasites. Activation of tumoricidal and microbicidal effector mechanisms requires stimulation of macrophages with macrophage-activating factors (MAF). One such MAF is interferon γ (IFN-γ). In some assays, substantial activity of IFN-γ on murine macrophages, however, is only observed in synergy with lipopolysaccharide (LPS) or other cytokines (1). In addition, certain cytokines have been shown to induce monocyte or macrophage activation in the absence of IFN-γ (2-5). We previously described lymphokines in the supernatant of a murine T cell clone that synergized with IFN-γ in the induction of tumoricidal and schistosomulicidal murine macrophages (1). We called this lymphokine(s) macrophage cytotoxicityinducing factor 2 (MCIF2)(1). A candidate for MCIF2 was lymphotoxin (LT), because the T cell clone supernatant contained high amounts of LT. LT is functionally homologous and structurally related to the macrophage product tumor necrosis factor (TNF). Therefore, we tested whether recombinant (r) LT or rTNF can function as MAF. We report here that rLT or rTNF synergize with rIFN-γ in the induction of tumoricidal and schistosomulicidal murine macrophages.     

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.     

Interferon beta, a cofactor in the interferon gamma production induced by gram-negative bacteria in mice

The interferon (IFN) gamma production of splenocytes from closely related C57BL/10ScSn (Sn) and C57BL/10ScCr (Cr) mice was compared. Concanavalin A and CD3 monoclonal antibodies induced high levels of IFN- gamma in both Sn and Cr splenocytes. By contrast, treatment with gram- negative bacteria induced IFN-gamma only in Sn splenocytes; in Cr splenocytes, the IFN-gamma response was heavily impaired. The IFN-gamma induction by bacteria requires the cooperation of IFN-gamma-producing cells with macrophages. Depletion of macrophages from Sn splenocytes resulted in the loss of ability to produce IFN-gamma after bacterial stimulation. Reconstitution with new Sn macrophages restored the IFN- gamma responsiveness, whereas reconstitution with Cr macrophages failed to do so. Normal function of IFN-gamma-producing cells and a defective function of macrophages of Cr mice was demonstrated by evidence showing that whole or macrophage-depleted Cr splenocytes, when supplemented with Sn macrophages, acquire the ability to produce IFN-gamma in response to bacteria. A similar effect was achieved by supplementing Cr splenocytes with supernatants of bacteria-stimulated Sn macrophages or with recombinant murine IFN-beta or IFN-alpha. Preincubation of active macrophage supernatants with antibodies to IFN-beta suppressed the helper activity for Cr splenocytes. Moreover, the bacteria-induced production of IFN-gamma by Sn splenocytes could be inhibited by antibodies to murine IFN-beta. The results provide evidence that IFN- beta is an important cofactor of IFN-gamma induction, which is not induced in Cr mice by gram-negative bacteria.     

Expression of a new cell surface antigen on activated murine macrophages

A macrophage cell-surface antigen associated with pyran and Corynebacterium parvum-activated macrophages and P388D1 cells but not detectable on normal or glycogen and thioglycollate-elicited murine macrophages has been described. The antigen was demonstrated both by complement-mediated cytotoxicity and immunofluorescence, using an appropriately absorbed rabbit antiserum to P388D1. This antiserum should enable the characterization of activated macrophage cell populations on an individual cell basis and should be a useful probe to study the interactions of macrophages with tumor cells and the relationship of activation to cell-surface changes.     

Interleukin 4 potently enhances murine macrophage mannose receptor activity: a marker of alternative immunologic macrophage activation.

Expression of the macrophage mannose receptor is inhibited by interferon gamma (IFN-gamma), a T helper type 1 (Th-1)-derived lymphokine. Interleukin 4 (IL-4), a Th-2 lymphocyte product, upregulates major histocompatibility class II antigen expression but inhibits inflammatory cytokine production by macrophages. We have studied the effect of IL-4 on expression of the macrophage mannose receptor (MMR) by elicited peritoneal macrophages. We found that recombinant murine IL-4 enhances MMR surface expression (10-fold) and activity (15-fold), as measured by the respective binding and degradation of 125I-mannose-bovine serum albumin. Polymerase chain reaction analysis of cDNAs from purified primary macrophage populations revealed that MMR, but not lysozyme or tumor necrosis factor alpha, mRNA levels were markedly increased by IL-4. The above effects were associated with morphologic changes. These data establish IL-4 as a potent and selective enhancer of murine MMR activity in vitro. IL-4 induces inflammatory macrophages to adopt an alternative activation phenotype, distinct from that induced by IFN-gamma, characterized by a high capacity for endocytic clearance of mannosylated ligands, enhanced (albeit restricted) MHC class II antigen expression, and reduced proinflammatory cytokine secretion.     

Contrasting effect of alpha/beta- and gamma-interferons on expression of macrophage Ia antigens

IFN-gamma is known to induce the expression of Ia antigens on macrophages. We found that murine IFN-alpha and -beta blocked the effects of IFN-gamma in a dose-dependent manner. The antagonistic effect of IFN-alpha and -beta was observed even when macrophages were prestimulated with IFN-gamma. These inhibitory effects of IFN-alpha or -beta were blocked by their respective antibodies. The block exerted by IFN-alpha/beta was similar whether Ia levels were monitored by immunofluorescence with anti-Ia mAb, or by stimulation of freshly sensitized, alloreactive T lymphoblasts. Adherent macrophage-rich populations from newborn mice were incapable of expressing Ia antigens following stimulation with IFN-gamma, and would inhibit the response of adult macrophages to this lymphokine. Addition of anti-IFN-beta mAb, but not anti-IFN-alpha allowed newborns' macrophages to express Ia in response to IFN-gamma, and ablated the suppressive activity toward adult cells. These results indicate that IFN-alpha and -beta, which can be produced in the course of self-defense responses and during ontogeny, may contribute to the down-regulation of macrophage Ia expression.     

Induction of interleukin 1 secretion and enhancement of humoral immunity by binding of human C5a to macrophage surface C5a receptors

The mechanism by which human C5a anaphylatoxin augments the primary humoral response of murine splenocytes to antigen has been investigated. Culture supernatants were generated from splenic adherent cells or macrophage cell lines after exposure to a brief pulse of human C5a. Supernatants from the macrophage-like cell line P388D1, which bears surface receptors for C5a, enhance the PFC response to antigen, whereas those from the closely related cell line P388, which lacks surface receptors for C5a, fail to cause enhancement. Supernatants from splenic adherent cells, which also bear C5a receptors, similarly augment the SRBC response. Active supernatants, but not those devoid of activity, were shown to contain interleukin 1 (IL-1) activity by both the thymocyte mitogenesis and thymocyte costimulator assays. None of the supernatants contained IL-2 activity. These observations suggest that the recently described role of human C5a as an immunopotentiating modulator is mediated by its ability to induce production of IL-1 upon binding to specific receptors at the macrophage cell surface.     

Murine gamma interferon activates the release of a macrophage-derived Ia-inducing factor that transfers Ia inductive capacity

In this report we demonstrate that when the murine macrophage tumor cell line P- 388D1 is incubated for 48-72 h with either concanavalin A-stimulated rat spleen cell supernatant or cloned murine immune interferon (IFN-gamma), the cultured cells release a cell-free factor activity that in turn induces the cell surface expression of Ia antigen on the murine monocyte cell line WEHI-3. This IFN-gamma-stimulated, Ia-inducing activity cannot be blocked with an anti-IFN-gamma heteroantiserum that does block the induction of Ia expression on WEHI-3 by both cloned murine IFN-gamma and rat Con A supernatant. The Ia-inducing factor ( IaIF ) generated from P- 388D1 after stimulation by IFN-gamma does not demonstrate any antiviral activity. The P- 388D1 -derived IaIF is not shed plasma membrane Ia glycoprotein molecules, as demonstrated by the inability of the active component to bind specifically to an anti-I-Ad affinity column or to a protein A column after the active supernatant is first treated with an excess of anti-I-E/Cd,k monoclonal antibody.     

Augmentation of macrophage complement receptor function in vitro. IV. The lymphokine that activates macrophage C3 receptors for phagocytosis binds to a fucose-bearing glycoprotein on the macrophage plasma membrane

Macrophage receptors for the third component of complement (C3) are normally immobilized and unable to diffuse within the cell's plasma membrane and, even though they promote avid particle binding, are unable to promote phagocytosis of C3-coated particles. We have previously identified a lymphokine that activates macrophage C3 receptors for phagocytosis and have found that it acts by freeing the receptors so that they can diffuse within the macrophage plasma membrane. It seemed likely to us that the initial lymphokine-macrophage interaction would occur at the macrophage surface, perhaps via a specific lymphokine receptor. Since the binding of many ligands to cells is mediated by cell surface glycoproteins, we examined the protein and sugar requirements for murine peritoneal macrophages to respond to the lymphokine. Macrophages treated with the neutral protease Dispase lost the ability to respond to the lymphokine, and inclusion of L-fucose in the incubation medium containing lymphokine and macrophages inhibited markedly the macrophages' response to the lymphokine, suggesting that the lymphokine exerts its effects by first binding to fucose residues on a glycoprotein receptor on the macrophage surface. Further evidence for the essential role of macrophage surface fucose was obtained by demonstrating that pretreatment of macrophages with either fucosidase or gorse lectin, a fucose-binding lectin, strikingly disabled the cells from responding to the lymphokine. All treatments that prevented lymphokine activation of macrophage C3 receptors for phagocytosis also prevented lymphokine-induced C3 receptor mobility. These results strongly suggest that the lymphokine binds to a fucose-bearing macrophage surface glycoprotein, perhaps a specific lymphokine receptor. They also strengthen our hypothesis that, for a receptor to be able to promote phagocytosis, it must be able to diffuse within the macrophage plasma membrane.     

Studies on the mechanisms of macrophage activation. II. Parasite destruction in macrophages activated by supernates from concanavalin A- stimulated lymphocytes

Activation of mouse peritoneal exudate macrophages, as evidenced by destruction of the intracellular protozoan parasite Leishmania enriettii, was obtained by incubation with supernates from concanavalin A (Con A)-stimulated syngeneic spleen cells. Parasites were not destroyed in macrophages exposed to control media. Supernate-induced activation was independent of the presence of Con A. The activating principle (macrophage activating factor, or MAF) was produced by Con A-stimulated lymphocytes in presence or absence of serum. In absence of serum, MAF synthesis was highest at Con A concentrations far below those required in serum-containing media. MAF production was reduced at Con A concentrations of 10 microgram/ml or above, probably a result of toxicity of the lectin for lymphocytes. MAF was detectable after 24 h of lymphocyte stimulation and increased up to 72 h; production appeared to be independent of DNA synthesis. Serum-free MAF was inactive when tested as such on macrophages. Full activity could be restored by addition of nanogram amounts of endotoxin or of FCS before assay. Endotoxin also considerably potentiated MAF activity in serum-containing supernates. Full intracellular parasite destruction was observed after contact of macrophages with MAF for 20 h. The continuous presence of MAF was not necessary for activation; a 10-h pulse was sufficient to induce macrophages to destroy all intracellular microorganisms within the next 38 h.     

Synthesis of complement components (C3, C2, B and C1-inhibitor) and lysozyme by human monocytes and macrophages

The synthesis of C3, C2, factor B (B) C1-inhibitor and lysozyme has been studied in monocytes and macrophages isolated from the synovial fluids of patients with rheumatoid arthritis. Concentrations of all 5 proteins in culture supernatants were measured by the sandwich ELISA technique. Kinetic studies showed that only lysozyme and C3 could be detected in monocyte culture supernatants on the first day of culture, whereas C2, B and C1-inhibitor were not present until the third day. In contrast all 5 proteins could be detected in the supernatants of macrophage cultures on day 1. In both monocyte and macrophage cultures synthesis of lysozyme and C1-inhibitor continued throughout the culture period, whereas synthesis of C2, B and C3 appeared to be reduced after the fifth day in culture. Quantitative studies showed that the secretion rates of lysozyme (4,700 X 10(3) molecules/cell/hr) was similar in monocytes and macrophages. Synthesis rates for all 4 complement components in monocyte cultures were less than 0.2% of that for lysozyme. Although the synthetic rates were higher in macrophages, even then they constituted less than 2% of the rate for lysozyme. Synthetic rates for complement components, but not lysozyme, were increased by BSA-anti-BSA antigen-antibody complexes and reduced by serum-treated complexes. Although the functional activity of monocyte B was similar to that for serum, the activity of monocyte C2 was 5 times that of serum C2. As C42 formed with monocyte C2 had a half-life of 13.5 min at 30 degrees C, compared with 4.5 min for the enzyme formed with serum C2, it is probable that monocyte C2 is oxidized by the oxygen products of these cells.     

Function and regulation of a murine macrophage-specific IgG Fc receptor, Fc gamma R-alpha

Ligand binding specificities of two cloned murine Fc gamma Rs (Fc gamma R-alpha, Fc gamma R-beta [9]) were determined by gene transfer into Fc gamma R negative cell lines. Both receptors were expressed as full-length molecules capable of IgG immune complex binding that was inhibitable by the mAb 2.4G2. The ligand binding profiles of these receptors were indistinguishable whereby both bound immune-complexed mouse IgG1, IgG2a, and IgG2b, but not IgG3. Neither receptor could bind monomeric IgG2a, indicating these receptors to be low-affinity IgG Fc receptors. Accumulation of the Fc gamma R-alpha mRNA can be induced with murine IFN-gamma at a concentration of 200 U/ml in the macrophage-like cell lines RAW 264.7 and J774a. The time course for induction indicates that the mRNA accumulation is transient but does not return to the uninduced level even after 50 h of treatment. Fc gamma R-beta mRNA was not induced by IFN-gamma, rather its expression was down modulated in mouse peritoneal macrophages. Both RAW and J774a cells lines exhibited increased receptor levels after IFN-gamma stimulation as measured by 125I-2.4G2 and ligand binding. In the absence of IFN-gamma, the RAW and J774a cell lines were minimally phagocytic, while P388D1 cells were actively phagocytic. In the presence of IFN-gamma, however, RAW 264.7 and J774a cells were induced to become actively phagocytic. Induction of Fc gamma R-alpha mRNA and protein by IFN-gamma may be part of the process by which macrophages become activated to engulf antibody-coated particles.     

Distinct murine macrophage receptor pathway for human triglyceride-rich lipoproteins.

Murine P388D1 macrophages have a receptor pathway that binds human hypertriglyceridemic very low density lipoproteins (HTG-VLDL) that is fundamentally distinct from the LDL receptor pathway. Trypsin-treated HTG-VLDL (tryp-VLDL), devoid of apolipoprotein (apo)-E, fail to bind to the LDL receptor, yet tryp-VLDL and HTG-VLDL cross-compete for binding to P388D1 macrophage receptors, indicating that these lipoproteins bind to the same sites. The specific, high affinity binding of tryp-VLDL and HTG-VLDL to macrophages at 4 degrees C is equivalent and at 37 degrees C both produce rapid, massive, curvilinear (receptor-mediated) triglyceride accumulation in macrophages. Ligand blots show that P388D1 macrophages express a membrane protein of approximately 190 kD (MBP190) that binds both tryp-VLDL and HTG-VLDL; this binding is competed by HTG-VLDL, trypsinized HTG-VLDL, and trypsinized normal VLDL but not by normal VLDL or LDL. The macrophage LDL receptor (approximately 130 kD) and cellular uptake of beta-VLDL, but not MBP 190 nor uptake of tryp-VLDL, are induced when cells are exposed to lipoprotein-deficient medium and decreased when cells are cholesterol loaded. Unlike the macrophage LDL receptor, MBP 190 partitions into the aqueous phase after phase separation of Triton X-114 extracts. An anti-LDL receptor polyclonal antibody blocks binding of HTG-VLDL to the LDL receptor and blocks receptor-mediated uptake of beta-VLDL by P388D1 cells but fails to inhibit specific cellular uptake of tryp-VLDL or to block binding of tryp-VLDL to MBP 190. Human monocytes, but not human fibroblasts, also express a binding protein for HTG-VLDL and tryp-VLDL similar to MBP 190. We conclude that macrophages possess receptors for abnormal human triglyceride-rich lipoproteins that are distinct from LDL receptors in ligand specificity, regulation, immunological characteristics, and cellular distribution. MBP 190 shares these properties and is a likely receptor candidate for the high affinity uptake of TG-rich lipoproteins by macrophages.     

Therapeutic concentrations of glucocorticoids suppress the antimicrobial activity of human macrophages without impairing their responsiveness to gamma interferon.

By exposing human blood-derived macrophages and alveolar macrophages in vitro to dexamethasone, we showed in these studies that glucocorticoids markedly suppress the antimicrobial activity of macrophages but not macrophage activation by lymphokines. As little as 2.5 X 10(-8) mol/liter of dexamethasone prevented macrophages from inhibiting germination of Aspergillus spores or from eliminating ingested bacteria such as Listeria, Nocardia, or Salmonella. Damage to macrophage function was inhibited by progesterone and appeared to be receptor-mediated. In accordance with in vivo observations, dexamethasone required 24-36 h to suppress antimicrobial activity. While glucocorticoids interfered with base-line activity of macrophages, dexamethasone concentrations comparable to drug levels in patients had no effect on macrophage activation. Proliferating lymphocytes and gamma-interferon thus increased the antimicrobial activity of phagocytes exposed to glucocorticoids over that of control cells. Macrophage activation and correction of the dexamethasone effect by gamma-interferon, however, was dependent on the pathogen. The lymphokine enhanced the antimicrobial activity of dexamethasone-treated macrophages against Listeria and Salmonella but not against Aspergillus or Nocardia. Dexamethasone-induced damage to the antimicrobial activity of human macrophages in vitro parallels observations that glucocorticoids render laboratory animals susceptible to listeriosis and aspergillosis by damaging resident macrophages. Suppression of macrophage antimicrobial activity should thus be considered when treating patients with glucocorticoids; its prevention by gamma-interferon might be beneficial for some but not all pathogens.     

Role of interleukin 2, interleukin 4, and alpha, beta, and gamma interferon in stimulating macrophage antibody-dependent tumoricidal activity

Pretreatment of murine peritoneal exudate macrophages with 1-5 U/ml rIFN-gamma or rIL-2, or higher concentrations of IFN-alpha or IFN-beta greatly stimulated ADCC to Rl lymphoma targets. The assay was direct counting of viable target cells after 9 and 24 h using an E/T ratio of 5:1. 2d of pretreatment was optimal for enhancing ADCC. rIL-4 was inactive and IL-4-depleted Con A-induced spleen lymphokine retained its ADCC-stimulating activity. Antibody to IFN-gamma blocked the ADCC-promoting effect of the lymphokine, suggesting a major role for this factor.