Products of activated lymphocytes. I. The use of radiolabeling techniques in the characterization and partial purification of the migration inhibition factor of the guinea pig

Mononuclear Phagocytes, Cellular Immunity, and Nobel Prizes: A Historic Perspective

The mononuclear phagocyte system includes monocytes, macrophages, some dendritic cells, and multinuclear giant cells. These cell populations display marked heterogeneity depending on their differentiation from embryonic and bone marrow hematopoietic progenitors, tissue location, and activation. They contribute to tissue homeostasis by interacting with local and systemic immune and non-immune cells through trophic, clearance, and cytocidal functions. During evolution, they contributed to the innate host defense before effector mechanisms of specific adaptive immunity emerged. Mouse macrophages appear at mid-gestation and are distributed throughout the embryo to facilitate organogenesis and clear cells undergoing programmed cell death. Yolk sac, AGM, and fetal liver-derived tissue-resident macrophages persist throughout postnatal and adult life, supplemented by bone marrow-derived blood monocytes, as required after injury and infection. Nobel awards to Elie Metchnikoff and Paul Ehrlich in 1908 drew attention to cellular phagocytic and humoral immunity, respectively. In 2011, prizes were awarded to Jules Hoffmann and Bruce Beutler for contributions to innate immunity and to Ralph Steinman for the discovery of dendritic cells and their role in antigen presentation to T lymphocytes. We trace milestones in the history of mononuclear phagocyte research from the perspective of Nobel awards bearing directly and indirectly on their role in cellular immunity.

Generation and characterization of a monoclonal antibody (1C5) to human migration inhibitory factor (MIF)

A monoclonal antibody was raised in mice against human MIF of the Mr 14,000 kd, produced by Concanavalin A-stimulated peripheral blood mononuclear cells. A hybridoma (1C5) secreting an IgG 1 antibody was selected which binds, yet does not neutralize MIF in the macrophage migration assay. MIF activity may be released from immobilized antibodies by acidic buffer elution. The eluate consists of three major bands at Mr 8,000, 14,000 and 28,000 as revealed by SDS-polyacrylamide gel electrophoresis and molecular sieve chromatography (HPLC). By radioimmunoassay and enzyme-linked immunoassay, it could be shown that the antibody binds material with isoelectric points of 4.5 to 5.0 and of 3.0, which coincides precisely with the biological activities. Similar congruencies between the distribution of biologically reactive and binding material were found in molecular sieve and ion exchange chromatography. It is concluded that the antibody 1C5 reacts with most molecular weight entities of MIF which seem to be structurally related and which display similar characteristics as described for guinea pig and mouse MIF.

Chronic relapsing experimental allergic encephalomyelitis. The presence in the cerebrospinal fluid of factors chemotactic for monocytes

Cerebrospinal fluid (CSF) was removed from guinea pigs with chronic relapsing experimental allergic encephalomyelitis (CR-EAE) and control inoculated animals by puncture of the cisterna magna. The fluid from 7/8 animals in relapse and 2/4 animals in remission phases of CR-EAE was found to promote the migration of peripheral blood monocytes through a 5-micron pore diameter polycarbonate membrane filter. Monocytes were also found to orient towards the migration-stimulating CSF in a gradient formed between such fluid and CSF derived from a control animal, thereby indicating the presence of a chemotactic factor. The factor responsible for promoting monocyte migration had a molecular weight of between 50 000 and 300 000 as defined by ultrafiltration. The results are discussed in relation to the known pathohistological features of the chronic relapsing disease.

Macrophage aggregation factor: some properties

The lymphokine activity, macrophage aggregation factor (MAgF) has been investigated further. Activity was consistently found in 24 hr test, but not control, spleen cell culture supernatants. This was higher after dialysis against water, than in the original culture supernatants. MAgF was heat-stable, inactivated by alpha-chymotrypsin, partially inactivated by trypsin and not affected by neuraminidase. Activity was recovered from the supernatant after protein precipitation with 1 M perchloric acid, leading to a modest purification. Activity was only marginally reduced after treatment with periodate, and was not absorbed by Concanavalin A-Sepharose. Polyacrylamide gel electrophoresis showed that MAgF migrated cathodally to albumin. Aggregation, as measured in a batch centrifugation assay, was an expression both of cell-substrate and cell--cell adhesion.

Modulation of macrophage functions by lymphokines

Macrophage migration inhibitory factors (MIFs) of mouse and guinea pig have been thoroughly characterized with regard to molecular weight and isoelectric points. Several molecular weight species have been identified. In a comparative study with purified MIFs it was found that these molecules were distinct from a series of other lymphokines, particularly so from macrophage activating activities. Investigations on the molecular weight heterogeneity of MIF have led us to a transglutaminase-like activity which was found to be expressed in certain subsets of macrophages. The question whether low molecular weight factors are polymerized by this enzyme to oligomers is further investigated. Studies on the induction by lymphokines of interferon and plasminogen activator revealed a great heterogeneity of responding macrophages. In studies on the biological basis of the functional heterogeneity of macrophages, the question was investigated whether the heterogeneity was due to different macrophage subpopulations or to intermediate relatively stable phenotypes on their way to maturity and senescence. To approach this question, the bone marrow liquid culture system was used as a developing system. Our data are summarized in a unifying model which takes into account the different constitutive and inducible functions during the cell cycle. Accordingly, lymphokines may act either as differentiation signals, as mitogens or activating signals.

Purification of guinea pig pH 3 migration inhibitory factor

Macrophage migration inhibitory factor (MIF) from the guinea pig was recently shown to reside in two discrete and separable proteins referred to as pH 3 MIF and pH 5 MIF. One subfraction of pH 3 MIF has now been purified to apparent homogeneity from supernatants of stimulated lymph node cells. To monitor purification, biosynthetically radiolabeled MIF was prepared. Sensitized lymphocytes were stimulated in the presence of [3H]leucine by concanavalin A to produce radiolabeled mediators. MIF was purified approximately 30,000-fold from the culture fluid by using gel filtration, sucrose density gradient electrophoresis, isoelectric focusing, and hydrophobic affinity chromatography. This procedure yielded a single 3H-labeled polypeptide with an apparent Mr of 35,000 that coincides with MIF activity.

Partial characterization of murine and monkey helper factor to a streptococcal antigen

Helper factors specifically stimulating cooperative antibody responses by normal mouse spleen cells to a dinitrophenylated protein antigen from Streptococcus mutans (DNP-SA) were produced in vitro from monkey peripheral blood leucocytes and mouse spleen cells. The factors were partially characterized by gel filtration on Sephadex G-75, isoelectric focusing, treatment with heat and degradative enzymes and binding to specific immunoadsorbents. Gel filtration of both the monkey and mouse factors showed coelution with human serum albumin, suggesting a molecular weight of approximately 70,000. The isoelectric points fell within the range of 4.9-5.2 for monkey and 6.4-6.7 for the mouse helper factors. The glycoprotein nature of both factors was suggested by their lability to heat and sensitivity to pronase and neuraminidase. The factors carried a small fragment of the stimulating antigen and showed specific binding to SA but not to keyhole limpet haemocyanin (KLH). Monkey factor bound to rabbit antisera directed against the Fc portion of monkey IgM, but not to the IgG or IgA isotypes. The mouse factor contained determinants coded for by the I-Ak but not I-Jk subregion of the MHC. Both factors were absorbed by an antiserum to helper factor raised in rabbits against a KLH-specific mouse helper factor as immunogen. A corresponding antiserum to suppressor factor failed to adsorb either factor. This emphasizes the specific identities of helper and suppressor factors and suggests an evolutionary relationship between those derived from monkey and mouse leucocytes.

The biochemistry and in vitro activity of soluble factors of activated lymphocytes

Activated lymphocytes release numerous products which are either synthesized de novo or in increased amounts; some of these products play a role in the regulation of the immune response and are designated as mediators of cellular immune reactions or lymphokines. The first lymphokine described was the macrophage migration inhibitory factor (MIF) which has been studied most extensively with regard to its chemical and biological properties. Using sensitive radiolabelling techniques and an antiserum against highly purified fractions of MIF we were able to identify several products of activated guinea pig lymphocytes with different molecular weights of 15.000, 30.000, 45.000, 60.000 which all had an isoelectric point of 5.2 and were all inhibitory to macrophage migration. It is suggested, that these molecules are oligomers of a common subunit of molecular weight 15.000. It was further shown, that molecules of the same physical-chemical and serological characteristics are produced by activated B-cells, L2C leukemia cells and growing fibroblasts, thus further substantiating earlier reports on the production of MIF by lymphoid and non-lymphoid cells. The described molecules were also shown not to contain determinants of the major histocompatibility complex and to be distinct from lymphotoxin, another lymphocyte activation product. It is concluded, that MIF is not a single molecule but rather a system of structurally related molecules. Their interaction with macrophages and possible relationships to macrophage activating factor is discussed.

Two mechanisms of cell-mediated cytotoxicity: Ca++ transport modulation by lymphotoxin and transmembrane channel formation by antibody and nonadherent spleen cells

Lymphotoxin is a protein with a MW of 45,000 daltons derived from activated lymphocytes that kills target cells nonspecifically. Kinetic studies indicate that there is a lag period of about 4 hours before cytotoxicity becomes apparent, even at high concentrations of lymphotoxin. Therefore, the role of lymphotoxin in cell-mediated cytotoxicity would be restricted to situations in which more rapid mechanisms are not operative. It has found that lymphotoxin increases the rate of 45Ca++ uptake by the mouse L-cells used as targets. This effect and the cytotoxicity are abrogated by ouabain. A lymphotoxin-resistent L-cell mutant did not display the 45Ca++ uptake effect. It is not known whether the Ca++ effect is primary or secondary. Neutralization experiments with anti-lymphotoxin have indicated that there are at least two distinct pathways by which immune lymphocytes can destroy target cells in vitro--one that involves secretion of a nonspecific soluble factor, i.e., lymphotoxin, and another that probably requires intimate contact between the plasma membranes of the target and killer cells. This "membrane contact" mechanism may involve formation of channels in the target cell membranes. The transmembrane channel concept is a working hypothesis that is based on experiments by Henkart and Blumenthal in which it was found that antibody and lymphocytes jointly produce ion-conducting channels in planar bilayers of "oxidized cholesterol." In order to supplement and extend this approach we have made an exploratory study of 86Rb+ and 51Cr marker release from lecithin/cholesterol/dicetyl phosphate liposomes by antibody and nonadherent mouse spleen cells. Evidence is presented indicating that the antibody and cells cause direct synergistic marker release from liposomes into the fluid medium. This indicates that they have the capacity to damage phospholipid bilayers. Hence, it seems worthwhile to conduct further studies of the liposome model in order to uncover the mechanism of membrane damage and to assess its relevance to cell-mediated cytotoxicity.

Studies on guinea-pig macrophage migration inhibitory factor (MIF). I. Glycoprotein nature and net charge

Guinea-pig macrophage migration inhibitory factor (MIF), obtained by the stimulation of sensitized lymph node cells with tuberculin PPD, was characterized as a glycoprotein by the following criteria: (a) its activity is destroyed by 0.02 M sodium periodate; (b) when MIF-containing culture fluids are subjected to precipitation by perchloric acid (final concentration 1 M), the inhibitory activity is recovered in the supernatant; and (c) MIF binds to Sepharose-linked concanavalin A and can be eluted with methyl-alpha-D-glucopyranoside. When MIF-containing culture supernatants are fractionated by isoelectrofocussing, migration inhibitory activity is recovered in a fraction with an isoelectric point of 4.4--4.6.

Partial purification of guinea pig MIF by affinity column chromatography using macrophages

First we have confirmed the previous observation that the macrophage migration inhibitory factor (MIF) was adsorbed on normal peritoneal macrophages when they were incubated at 4 C for 60 min. It was found that macrophages fixed with 2% glutaraldehyde gave more reproducible results than viable cells in terms of "adsorption" of guinea pig MIF. The adsorption was achieved more completely at 37 C than at 4 C, indicating that this reaction is a temperature-dependent phenomenon. Using these glutaraldehyde-fixed macrophages, a kind of cell-affinity column was successfully developed. The guinea pig MIF preparation lost its activity when it was passed through this affinity column, and MIF adsorbed on the column was recovered by elution with 0.1 M (L)-fucose of 0.1 M (D)-glucose. Such MIF active eluate was found to be at least 30--40 fold more pure than the original MIF preparation which had been previously fractionated according to its molecular weight. Therefore, this type of macrophage-affinity column may be useful for the purification of MIF.

Purification of antigen-dependent macrophage migration inhibition factor (MIF) from lymph draining a tuberculin reaction

An antigen-dependent factor showing migration inhibition (MIF) and gold uptake stimulation (GUS) activities which has been previously described (Lowe & Lachmann, 1974) has been further purified from efferent lymph collected from cannulated nodes of BCG-sensitized sheep undergoing a delayed hypersensitivity response to PPD. During purification, fractions containing MIF activity also exhibited GUS activity. Initial purification by salt precipitation showed that antigen-dependent MIF activity was in the 40-90% ammonium sulphate precipitate. Non-specific activity and contaminating immunoglobulin were found in the 0--20% and 20--40% precipitates. Gel filtration on Sephadex G-200 and affinity chromatography on Concanvalin A-Sepharose have shown that antigen-dependent MIF is a glycoprotein of approximately 70,000 molecular weight (Lowe & Lachmann, 1974). Traces of contaminating antibody in the glycoprotein fraction were removed by immuno-adsorption on monospecific anti-sheep IgG-Sepharose. Antigen-dependent MIF was also purified by affinity chromatography on PPD-Sepharose. The eluted fractions with all the antigen-specific activity, contained less than 1% of the applied material. Analysis by polyacrylamide gel electrophoresis showed that the major protein component in the purified MIF preparation has a molecular weight and electrophoretic mobility identical with that of sheep albumin. Although this represents a high degree of purification of antigen-dependent MIF it seems that albumin is still present as a contaminant and that the protein associated with MIF activity is present in trace quantities.

Use of a radioactive double labeling technique in the chemical analysis of the mediators of cellular immunity

Radioactive double labeling was adapted for the analysis of mediators of cellular immunity. Two identical lymphocyte cultures were simultaneously labeled with [3H]- or [14C]leucine. Each of the cultures was stimulated with antigen or mitogen. The combined supernatants were then subjected to various fractionation procedures. By determining the isotope ratio in each fraction it is possible to identify those products of activated lymphocytes that have been produced either de novo or in increased amounts. The method proved sensitive enough to detect lymphocyte activation products in supernatants of activated lymphocyte cultures from guinea pig, mouse, and man.

Human migration inhibitory factor: purification and immunochemical characterization

Using gel filtration and preparative isotachophoresis, the migration inhibitory factor (MIF) was highly purified from human lymphocytes activated with concanavalin A. MIF is an acidic protein with a mol wt of approximately equal to 25,000 daltons as determined by gel filtration and analytical polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The protein inhibits migration of macrophages in the capillary test and in addition, has a slowing effect on the electrophoretic mobility of guinea pig peritoneal macrophages. Rabbit antibodies specific for this protein, as determined by immunochemical techniques, neutralized the biological effect of MIF on migration and on the electrophoretic mobility of macrophages.

Antibodies to guinea pig lymphokines. III. Reactions with radiolabeled lymphocyte activation products

An antiserum raised against a purified fraction of guinea pig lymphokines exhibits marked in vivo properties; it suppresses delayed hypersensitivity reactions and binds migration inhibition factor (MIF) from supernatants of activated lymphocyte cultures in vitro. This serum was analyzed for specificity using a radioactive double labeling technique which distinguishes products synthesized either de novo or in increased amounts by stimulated lymphocytes. Combined supernatants of stimulated (concanavalin A or PPD) and unstimulated cultures labeled with either tritiated or [14C]leucine, respectively, were fractionated on Sephadex G-75. Pooled fractions were precipitated using the antibody sandwich technique, and solubilized precipitates were analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Using this procedure the anti-lymphokine serum recognized primarily three newly sythesized lymphocyte activation products with molecular weights of approximately 60 000, 45 000 and 30 000 daltons. By contrast, these molecules could not be detected in radiolabeled lymph node cells which had been solubilized with NP-40 detergnt. The isoelectric point of all three molecules was found to be 5.2 +/- 0.3. The previously determined characteristics (mol.wt. 45 000, pI 5.2) of MIF and the property of the anti-lymphokine serum to absorb MIF activity suggest an identity between MIF and one of the molecules. In view of the previously described in vivo effects of the anti-lymphokine serum it is concluded that at least one of these three molecules plays an important role in the early events of delayed-type hypersensitive reactions in vivo.

Radioactive labelling and characterization of the products of activated mouse lymphocytes

For chemical characterization of the products of activated lymphocytes a radioactive double-label technique was developed which allows one to distinguish those products synthesized either de novo or in increased amounts by the stimulated culture. Spleen cells from Balb/c mice were cultured in serum-free medium in the presence or absence of concanavalin A and simultaneously labelled with radioactive leucine. Optimal culture conditions were established by determining parameters such as cell density, mitogen concentration, and kinetics of protein synthesis following stimulation. Combined supernatants of stimulated and unstimulated cultures each labelled with either [3H]leucine or [14C]leucine were fractionated on Sephadex G-75. Materials derived from control or stimulated supernatants both yielded a qualitatively similar radiolabelled profile. The isotope ratio of stimulated to nonstimulated culture, however, showed a broad peak at KD 0--.35 (approx. mol. wt 75000-20000) which was further analyzed by isoelectric focusing. Pools of every two fractions were focused in polyacrylamide gels at pH 3.5-10. By determining the isotope ratio, the isoelectric point, and the KD (mol wt), it was possible to distinguish at least 24 molecules which had been produced only, or in greater degree, by the stimulated culture.

A study of proteolysis as a possible mechanism for T-cell-mediated target cell lysis

The hypothesis that proteolysis is implicated in T-cell-mediated target cell lysis was tested in two ways: first, various inhibitors of protease activity were used either during or before the cytotoxicity test. Ovomucoid, TPCK, and PMSF proved to be not or only marginally inhibitory, whereas the considerable inhibitory action of TLCK was shown to most likely be a toxic effect of the inhibitor. Second, radioactive substrates for cathepsin activity were used, either free in the medium or fixed on the surface of the target cells, to detect a possible breakdown of these substrates by a release of intracellular cathepsins during the cytotoxicity test. Very little dialysable breakdown products were formed, and there was no difference between their amount in either a homologus or a heterologous system. It is concluded that proteolysis probably is not the mechanism by which target cells are killed. Alternative mechanisms are discussed.