Cellular cooperation in mitogen-induced human leukocyte inhibitory factor (LIF) synthesis.

Interactions between human T and B lymphocytes and between lymphocyte subpopulations and accessory cells in lymphokine synthesis were investigated. The cells were stimulated with leukoagglutinin (LA), concanavalin A (Con A), protein A (prot A) and anti-β₂-microglobulin (anti-β₂m). The presence of leukocyte inhibitory factor (LIF) in the culture supernatants was tested by the agarose-migration method. The results indicated that monocytes augmented LIF synthesis of T cells but suppressed that of B cells. Monocyte-helper effect was mediated by both cell-cell contact and soluble factors. In addition, T lymphocytes were found to augment B-cell LIF production. B lymphocytes enhanced Con A- but suppressed LA-induced LIF production by T cells. T-cell/B-cell collaboration was based on a direct cell-cell contact and no soluble factors were found.     

Human leukocyte inhibitory factor (LIF): two distinct molecular species.

Human leukocyte inhibitory factor or LIF was generated in vitro by stimulating blood lymphocytes with concanavalin A (Con A). The control and Con A active supernatants were partially purified by gel filtration on Sephadex G-100. The fraction containing LIF (68,000 daltons) activity was then subjected to isoelectric focusing (pH 3 to 10 ampholines) in a sucrose gradient. Two LIF activities were reproducibly recovered by this procedure. One molecular form was found to have an isoelectric point of approximately pH 5.0 and the other approximately pH 8.5. Both molecular species were rechromatographed on Sephadex G-75 and found to have the same apparent m.w. (68 to 75,000). Furthermore, the biologic activity of both factors was destroyed after treatment with diisopropylphosphofluoridate, suggesting that they may be esterases.     

Rat leukocyte inhibitory factor (LIF): Similarities to human LIF and generation by cells from rats with collagen-induced arthritis

Rat lymph node cells (LNC) produce a mediator which exhibits functional and physicochemical similarities to human leukocyte inhibitory factor (LIF). Measurement of LIF can be used to quantify cellular sensitivity in rats to foreign protein antigens or to a heterologous antigen in vitro. Concanavalin A-induced rat LIF has a molecular weight of 100,000-60,000 daltons and retains activity after heating to 56 °C for 30 min. Rat LIF is not synthesized in the presence of puromycin and appears to be a protein, since it is inactivated by treatment with chymotrypsin. Moreover, the activity of rat LIF is susceptible to the serine esterase inhibitor, diisopropylphosphofluoridate, but it is resistant to neuraminidase treatment. Finally, rat LIF preferentially inhibits the migration of rat and human polymorphonuclear leukocytes but not that of rat or guinea pig peritoneal exudate cells enriched for macrophages. Except for the more dispersed size of rat LIF, these properties are analogous to those described for human LIF. LIF activity is generated, in an antigen-specific manner, by LNC sensitized to ovalbumin or purified protein derivative of tuberculin when cultured with the antigen used for sensitization. LNC from rats rendered arthritic by prior intradermal (id) injection of native chick type II collagen in incomplete Freund's adjuvant produce LIF in response to this heterologous antigen. These studies delineate a new assay for cellular sensitivity in rats and provide additional evidence that cellular reactivity to type II collagen is present in this animal model of arthritis.     

Effects of leukocyte inhibitory factor (LIF) on neutrophil phagocytosis and bactericidal activity

Human leukocyte inhibitory factor (LIF) is a lymphokine initially defined by its ability to inhibit the random migration of neutrophils. We have recently demonstrated that LIF also potentiates a number of f-met-leu-phe-mediated functions as well as enhancing one Fc receptor-mediated function (antibody-dependent cellular cytotoxicity). In this paper, we have extended our studies involving the effects of LIF on the neutrophil, specifically its effect on phagocytosis and bactericidal activity. We demonstrate that LIF (2 U/ml) potentiates phagocytosis of opsonized heat-killed Staphylococcus aureus (up to 57.2%) and sheep erythrocytes (124.4%) as well as unopsonized latex particles (59.9%). Phagocytosis of opsonized sheep erythrocytes was inhibited by an anti-neutrophil Fc receptor antibody with control PMN but not using the LIF-treated PMN. LIF (1/2 to 1 U) also potentiates the killing of S. aureus by up to 51.6%. Higher concentrations of LIF (greater than or equal to 4 U) inhibits killing. These effects were shown not to be associated with an increase in Fc receptor availability. It is therefore possible that potentiation of these neutrophil activities by LIF may occur either as a result of increased receptor turnover or, more likely, secondary to an increase in nonspecific neutrophil adherence. These studies further support the concept that LIF may have an important role in vivo in inflammation and immunity.     

Effects of leukocyte inhibitory factor (LIF) on neutrophil mediated antibody-dependent cellular cytotoxicity

The human lymphokine, leukocyte inhibitory factor (LIF), was investigated for its effect on neutrophil-mediated antibody-dependent cellular cytotoxicity (ADCC) for K562 targets. Highly purified LIF (0.5 to 2 U/ml) induced a significant dose-dependent potentiation of neutrophil ADCC by up to 54.9% (p less than 0.001). Higher concentrations of LIF inhibited cytotoxicity. The degree of cytotoxicity was found to correlate (r = 0.99) with the increased secretion of superoxide after neutrophil-target cell interaction. Anaerobic conditions inhibited cytotoxicity mediated by both control and LIF-treated neutrophils. The latter observation lends support to the concept that enhanced ADCC was mediated through increased superoxide production and not through the induction of a separate pathway. Increased superoxide production may have resulted from an upregulation of the transduction mechanism leading to neutrophil stimulation through the Fc receptor. In addition, we demonstrated an increased capacity of the neutrophil to adhere to its target (average 3.3:1 effector:target ratio in untreated cells to 4.8:1 after treatment with LIF), and this may also have been responsible for the increase in the respiratory burst and subsequent enhanced ADCC. These observations provide potential support for an in vivo role for LIF in tumor immunity.     

The production of heterologous antibodies to the human lymphakine: leukocyte migration inhibitory factor (LIF).

Human leukocyte migration inhibitory factor (LIF) produced by concanavalin A-stimulated lymphocytes was partially purified by Sephadex G-100 chromatography and immunosorption of protein contaminants. This material was injected into two rabbits, and the IgG-IgA fractions of the resulting antisera (anti-LIF) neutralized LIF induced by antigen (PPD tuberculin) with as equal efficiency as that of LIF induced by mitogen. Anti-LIF activity was neither removed by absorption with control supernatant or normal human serum nor was it suppressed by absorption with lymphocytes or lymphoblasts. On the other hand, antibodies against human lymphoid cells (ALG) did not reduce LIF activity, indicating the difference between anti-LIF and classical ALG. In support of this, anti-LIF, in contrast to ALG, was not cytotoxic to lymphocytes, and it did not inhibit spontaneous T-rosette formation with sheep erythrocytes. In crossed immunoelectrophoresis using a conventional proteinstaining technique, only three precipitates appeared. None of these contained LIF. However, a protein migrating in the prealbumin region appeared to be specific for lymphocyte stimulation. The nature and significance of this product is unknown.     

Enhancement of the function of neutrophil type-1 and type-3 complement receptors by human leukocyte inhibitory factor (LIF)

The lymphokine leukocyte inhibitory factor (LIF) has previously been documented to enhance several neutrophil (PMN) functions, including stimulated chemotaxis and superoxide generation, phagocytosis and adherence of opsonized targets, and antibody-dependent cellular cytotoxicity. The present studies were designed to investigate the effects of LIF on PMN function mediated by the complement components C3b and C3bi. LIF induced a dose-dependent increase in superoxide production generated by opsonized zymosan (up to 97.1 +/- 31.4% at 16 U LIF/ml; P less than 0.01). While neither control nor LIF-treated PMN were capable of inducing phagocytosis of either C3b- or C3bi-opsonized sheep erythrocytes (E) directly, exposure to LIF caused a significant (P less than 0.05) increase in their adherence to E (137.4 and 59.4%, respectively). Specificity for complement receptor function was confirmed by the ability of anti-CR1 antibody to block adherence of LIF-treated PMN to EAC3b (77.0% inhibition) and anti-CR3 antibody to block adherence to EAC3bi (70.2% inhibition). Increased C3b and C3bi function may have been due, at least in part, to increased expression of their respective surface membrane receptors. Thus, using indirect immunofluorescence, LIF induced a 38.2% increase in fluorescence of the anti-CR1 antibody and a 96.1% increase in anti-CR3 binding. These studies describe an additional mechanism through which LIF may have an important pro-inflammatory role in vivo.     

Amplification of the activity of human leukocyte inhibitory factor (LIF) by the generation of a low molecular weight inhibitor of PMN leukocyte chemotaxis

Leukocyte inhibitory factor (LIF), which was derived from human peripheral blood lymphocytes by stimulation with concanavalin A ad partially purified by Sephadex G-100 gel filtration, inhibited the in vitro spontaneous migration and chemotaxis of human PMN leukocytes as assessed in a Boyden chamber micropore filter assay. The inhibitory activity was attributed to LIF, a principle defined in terms of its inhibition of PMN leukocyte migration from glass capillary tubes since it was preferentially directed to PMN leukocytes as compared to mononuclear leukocytes, exhibited a size comparable to LIF by gel filtration, and was inactivated by diisopropyl fluorophosphate in parallel with LIF. Incubation of PMN leukocytes with LIF released additional inhibitory activity, distinct from LIF, which resembled the neutrophil-immobilizing factor (NIF) by virtue of its approximate m.w. of 4000 by filtration on Sephadex G-25, inactivation by trypsin digestion, and preferential noncytotoxic inhibition of spontaneous migration and chemotaxis of PMN leukocytes as compared to mononuclear leukocytes. Thus LIF inhibits PMN leukocyte migration both by a direct action on the cells and by an amplification pathway that is mediated by low m.w. chemotactic inhibitors similar to NIF.     

Leukocyte inhibitory factor (LIF) potentiates neutrophil responses to formyl-methionyl-leucyl-phenylalanine

The ability of purified (80,000-fold) human leukocyte inhibitory factor (LIF) to modulate several formyl-methionyl-leucyl-phenylalanine (f-met-leu-phe)-induced neutrophil functions was evaluated. Although not affecting directed migration itself, at low concentrations (1/2 to 2 U/ml), LIF was demonstrated to potentiate chemotaxis induced by f-met-leu-phe (40.3% +/- 8.1) and to reduce the concentration of f-met-leu-phe necessary for maximal chemotaxis (10(-8) to 10(-9) M). Similarly, LIF did not directly induce the respiratory burst, but potentiated both superoxide generation (151.6% +/- 77) and hydrogen peroxide production (54.9% +/- 15.5) in the presence of f-met-leu-phe (10(-7) M). LIF was also shown to induce degranulation of neutrophil-specific granules in a dose-dependent manner. Neutrophil-specific granules have been shown to contain an intracellular pool of receptors for f-met-leu-phe, and on degranulation provide the surface membrane with a fresh source of receptors. Our data suggested that LIF potentiation of neutrophil stimulation by f-met-leu-phe might be mediated, at least in part, by increasing the number of available membrane receptors as a result of its ability to induce degranulation. Radioligand receptor analysis using f-met-leu-[3H] phe was performed, and LIF was shown to mediate an increase in receptors for f-met-leu-phe from an average of 18,600 on untreated cells to 27,000 after pretreatment with LIF. This increase in receptors could "sensitize" the neutrophils for f-met-leu-phe and possibly explain the potentiation of neutrophil stimulation observed in the presence of the ligand. LIF was also found to have a more generalized effect on the transduction of neutrophil activation stimuli, mediating a 35.8% increase in superoxide production after exposure to calcium ionophore. The data do not permit a determination as to whether the increase in receptor number is responsible for the potentiation of f-met-leu-phe-mediated function, or whether this occurs secondary to the more generalized effect on neutrophil stimulation transduction.     

Axotrophin and leukaemia inhibitory factor (LIF) in transplantation tolerance

Immune self-tolerance is controlled by a subset of T lymphocytes that are regulatory (Treg) and epigenetically programmed to suppress auto-reactive immune effector cells in vivo. By extrapolation, donor-specific transplantation tolerance might be controlled by donor-specific Treg that have acquired the appropriate epigenetic program for tolerance. Although such tolerance has yet to be achieved in man, proof of concept comes from mouse models where regulatory transplantation tolerance can be induced within the complex micro-environment of the spleen or draining lymph node. By studying whole spleen cell populations in a murine model of transplantation tolerance we have incorporated a complexity of environmental factors when looking for specific features that characterize tolerance versus aggression. This approach has revealed unexpected patterns of gene activity in tolerance and most notably that a novel stem cell gene, axotrophin, regulates T lymphocyte responsiveness both in terms of proliferation and in release of leukaemia inhibitory factor (LIF). Since LIF is a regulator of stem cells in addition to being a key neuropoietic cytokine, these preliminary results linking both axotrophin and LIF to transplantation tolerance lead us to propose that regulatory pathways encoded during the epigenetic development of Treg cells are related to pathways that regulate fate determination of stem cells.     

Suppression of leukocyte inhibitory factor (LIF) production and [3H]thymidine incorporation by concanavalin A-activated mononuclear cells.

The capacity of human mononuclear (MN) cells pretreated with concanavalin A (Con A) to suppress the activity of fresh phytohemagglutinin (PHA)-pulsed mononuclear cells was assessed. Con A-pretreated MN cells suppressed leukocyte inhibitory factor (LIF) activity in supernatants of PHA-pulsed cell cultures and [³H]thymidine incorporation by these cells. Suppression was obtained in both allogeneic and autologous systems with mitomycin-treated, irradiated, or untreated Con A-induced cells. Lymphocytes from two patients that, following treatment with Con A, did not suppress mitogen-induced proliferative response of normal cells also did not suppress LIF production.     

Use of benzoyl-L-phenylalanyl-L-valyl-L-arginine (3H) methyl ester as a sensitive and selective substrate for the human lymphokine, leukocyte migration inhibitory factor (LIF)

Human leukocyte migration inhibitory factor (LIF) appears to be a serine esterase and protease exhibiting specific affinity towards arginine esters and amides. On the basis of indirect evidence that an amide of the oligopeptide benzoyl-phenylalanyl-valyl-arginine might have high and selective affinity for LIF, we prepared an ester of this oligopeptide, benzoyl-phenylalanyl-valyl-arginine (3H) methyl ester (3H-BPVAME) for the direct measurement of LIF activity in a double-phase radio-enzyme assay. The hydrolysis of 3H-BPVAME followed enzyme-substrate kinetics in that the reaction was time-, temperature-, pH-, and concentration-dependent. 3H-BPVAME rpoved to be more selective and approximately 20 times more sensitive as a substrate for LIF than previously used radiolabeled substrates such as 3H-BAEE and 3H-TAME. Moreover, hydrolysis of 3H-BPVAME by partially purified LIF preparations was significantly inhibited by 10(-8) to 10 (-5) M of guanosine 3',5'-cyclic monophosphate (cGMP), further supporting the hypothesis that cGMP acts as a regulator of LIF activity. Inhibition of LIF-induced esterolysis was also provided by dibutyryl cGMP, but only at concentrations 10(-7) to 10(-5) M; 8-bromo cGMP and adenosine 3',5'-cyclic monophosphate were both ineffective. These results provide support for the use of 3H-BPVAME as a more selective substrate to detect esterase activity in LIF preparations than heretofore described and the possible development of a biochemical assay for the measurement of this lymphokine.     

Leukaemia inhibitory factor (LIF) is functionally linked to axotrophin and both LIF and axotrophin are linked to regulatory immune tolerance

Axotrophin (axot) is a newly characterised stem cell gene and mice that lack axotrophin are viable and fertile, but show premature neural degeneration and defective development of the corpus callosum. By comparing axot+/+, axot+/- and axot-/- littermates, we now show that axotrophin is also involved in immune regulation. Both T cell proliferation and T cell-derived leukaemia inhibitory factor (LIF) were suppressed by axotrophin in a gene-dose-dependent manner. Moreover, a role for axotrophin in the feedback regulation of LIF is implicated. This is the first evidence that fate determination mediated by LIF maybe qualified by axotrophin.     

Leukemia inhibitory factor (LIF): A growth factor with pleiotropic effects on bone biology

Historically, growth factors are denominated based on a specific biological activity. In many cases, these factors display a much broader spectrum of activities, especially when their effect is tested on various cell or tissue types. Consequently, names of certain factors are quite deceptive. A textbook example is leukemia inhibitory factor (LIF). LIF was initially described based on its ability to induce differentiation in the murine myeloid leukemia cell line M1. Later, LIF turned out to be a synonym for at least nine different factors defined on the basis of their effects on a variety of cell types including lymphomas, liver cells, embryonic stem cells and carcinoma cells, neurons, melanomas and osteoclasts. Apart from its differential effect on unrelated cell types and tissues, LIF induces biphasic effects on cells of the same “lineage” as well. Needless to say, LIF activity in these circumstances largely depends on the developmental stage of the target cells. An example is LIF activity on bone cells. Osteoclast as well as osteoblast activity is stimulated or suppressed by LIF depending on the developmental stage of the respective cells. This concept is of utmost importance in the evaluation of the seemingly opposing or contradictory effects of LIF in vitro as well as in vivo.