Studies on the effect of soluble lymphocyte products (lymphokines) on macrophage physiology. I. Early changes in enzyme activity and permeability.

Various cytochemical techniques have been used to quantitate the rapid effect of a partially purified, soluble product from lymphocytes (lymphokine) on normal guinea pig macrophages in vitro. Early changes in the utilisation of hydrogen liberated from the hexose monophosphate shunt and on cellular permeability were observed. The ability of the lymphokine to alter hydrogen utilisation was also seen in experiments on cryostat sections of guinea pig liver, suggesting that the cytochemical effects were not predetermined by changes at the membrane level. It is suggested that lymphokine-induced changes within the cell may reduce some biosynthetic activity affecting the cell membrane and this may in part reflect the decreased migrating ability of the cells. Increases in NADPH oxidation after lymphokine contact are discussed in relation to the bactericidal capacity of the cells.     

Changes in macrophage status in vivo during infection with and immunity to Leishmania enriettii

The changing status of peritoneal macrophages in guinea pigs infected with Leishmania enriettii has been examined. It was possible to demonstrate that, at certain times during a primary infection and following attempted reinfection of immune animals, the response of peritoneal macrophages to lymphokine contact in vitro was altered. At these times the harvested cells appeared to behave in vitro as if they had been at least partially activated in vivo before removal. They were unresponsive to lymphokine in the migration inhibition assay, and contact with lymphokine in culture caused a rapid increase in the level of glucose oxidation in these cells. It is suggested that changes in the response of macrophages to lymphokine in vitro may be one way of monitoring activation in vivo.     

Changes in macrophages in vivo induced by desensitization.

Peritoneal exudate macrophages were removed from animals sensitized to horse cytochrome c and from similar animals which had been desensitized with this antigen. The ability of lymphokine to induce migration inhibition and also alterations of the level of glucose oxidation in these cells has been examined. It was found that for a transient period after the desensitization, macrophages removed from the peritoneum were unresponsive to lymphokine in the migration inhibition assay. At the same time, culturing these cells with lymphokine for 1 hr caused a significant rise in their glucose oxidation activity. It is suggested from these results that desensitization may result in macrophage activation in vivo. This is discussed in relation to current concepts of the mechanisms of desensitization.     

Characterization of human chemotactic lymphokine production induced by mitogens and mixed leukocyte reactions using a new microassay.

Quantification of lymphokine production in vitro can be a useful tool in the evaluation of delayed hypersensitivity in various disease states. A micro-method for the measurement of chemotactic lymphokine production by human mononuclear leukocytes (MNL's) has been developed. MNL's are isolated on Ficoll-Hypaque gradients and cultured without plasma in microtiter plates. Culture supernatants are harvested through glass fibre filter paper under vacuum in a semi-automatic harvester. Chemotactic lymphokine activity in the supernatants is quantified in miniaturized Boyden chambers using human monocytes as responder cells. The production of chemotactic activity can be initiated by mixed leukocyte reactions as well as by soluble antigens or mitogens, and therefore may be a useful adjunct in tissue typing. Studies of lymphokine production in normal individuals indicate that these methods are quantitative, reproducible, and readily applicable to the study of this parameter of immune function in human disease.     

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.     

Suppression of lymphokine production: I. Macrophage-mediated inhibition of MIF production

Macrophages have been found to suppress the in vitro production by stimulated T lymphocytes of a lymphokine, migration inhibitory factor. When macrophages isolated from primary MSV-induced tumors were added to antigen-stimulated MSV-immune spleen cells, a complete suppression of MIF production was observed. This suppression was nonspecific, since MIF production by antigen-stimulated alloimmune spleen cells and by PHA-stimulated normal spleen cells was also inhibited. Suppressor macrophages could also be induced by inoculation with Corynebacterium parvum, whereas light mineral oil-induced peritoneal macrophages had no detectable effect on MIF production. The failure to detect MIF in the supernatants of stimulated cultures containing activated macrophages appeared to be due to inhibition of lymphokine production rather than to absorption or inactivation of MIF or to interference with the assay for detection of MIF. Macrophages were able to suppress MIF production only when added during the first 4–5 hr of culture and they had no effect when added later. These data show that activated macrophages can nonspecifically suppress lymphokine production and that this appears to be due to inhibition of an early step in lymphocyte stimulation.     

Eosinophils and immune mechanisms. IV. Culture conditions, antigen requirements, production kinetics and immunologic specificity of the lymphokine eosinophil stimulation promoter.

The culture conditions which contribute to the production of the lymphokine, eosinophil stimulation promoter (ESP), have been investigated. Spleen or lymph node cells from mice infected for 8–10 weeks with the helminth Schistosoma mansoni respond to challenge with a soluble egg antigenic preparation (SEA) from S. mansoni eggs by the elaboration of ESP into the culture medium. Exposure to as little as 0.1 μg of SEA elicits this response. Furthermore, 30 min of exposure to antigen is sufficient to stimulate subsequent ESP production. Production begins within 4 hr, is rapid for 12 hr, and continues for at least another 8 hr. The use of this information allows the standardization of ESP production to be such that the concentration of SEA is insufficient to interfere with the indirect assay of ESP upon eosinophil-rich peritoneal exudates from S. mansoni-infected mice. The specificity of the direct assay elicited by SEA was confirmed, and the ability of the lymphokine to stimulate eosinophil migration from eosinophil-rich peritoneal exudates from either S. mansoni-or Trichinella spiralis-infected mice was demonstrated.     

T cell induction of macrophage IL-1 during antigen presentation. Characterization of a lymphokine mediator and comparison of TH1 and TH2 subsets

We described in a previous study two pathways by which Th cells induced macrophage membrane IL-1(mIL-1) during Ag presentation. One pathway was lymphokine-independent and mediated by cell-cell contact. The second was lymphokine-dependent. We have now characterized this lymphokine and show that it belongs to the TNF family of proteins. All TH1 and most TH2 clones produced the lymphokine, although TH1 levels were markedly greater. Both types of clones also induced macrophage mIL-1 by cell-cell contact (i.e., in the absence of lymphokine release). Examination of macrophages by in situ hybridization showed that both IL-1 alpha and IL-1 beta mRNA were coordinately induced during Ag presentation to either TH1 or TH2 clones.     

Retrovirus-mediated immunosuppression. II. FeLV-UV alters in vitro murine T lymphocyte behavior by reversibly impairing lymphokine secretion

Murine splenocytes and cloned murine T cells were used to study the in vitro immunosuppressive effects of UV-inactivated feline leukemia virus (FeLV-UV) on lymphokine secretion. FeLV-UV can significantly depress the accumulation of IL 2 in cultures of Con A-stimulated C57BL/6 splenocytes and in cultures containing the alloreactive helper T cell clone B6D/2-2m plus Con A. Inhibition of lymphokine accumulation in these cultures could not be attributed to absorption or inactivation of IL 2 by the FeLV-UV or to the FeLV-UV-induced production of substances which interfere with the IL 2 bioassay. Thus, FeLV-UV appears to block production and/or secretion of IL 2 by a direct inhibitory effect on IL 2-secreting murine T lymphocytes. Additional studies indicate that FeLV-UV impairs IL 2 production only if added very soon after lymphocyte contact with lymphokine-inducing agents and that IL 2 secretion resumes when FeLV-UV is removed from the culture. FeLV-UV also impairs accumulation of MAF (interferon-gamma?) in cultures of Con A-stimulated C57BL/6 splenocytes and in cultures containing the alloreactive cytotoxic T lymphocyte clone B6D/2-7c plus Con A. The latter observation again suggests that FeLV-UV impairs lymphokine secretion by a direct effect on lymphokine-producing T lymphocytes. Furthermore, it suggests that FeLV-UV does not selectively impair production of IL 2 nor does it have selective inhibitory effects on helper T cells. Rather, FeLV-UV appears to have a general inhibitory effect on lymphokine production by T lymphocytes. Finally, concentrations of FeLV-UV which suppress MAF production by the CTL clone have little influence on the cytolysis mediated by the same cloned T cell population. Thus, the immunosuppressive influence of FeLV-UV is selective for phenomena associated with induction of new T lymphocyte functions, such as lymphokine secretion, and spares other immune functions already expressed by the same cells.     

The effect of levamisole on lymphocyte protein synthesis in vitro.

Human peripheral blood lymphocytes from normal donors were studied to determine the effect of levamisole, an immunostimulating agent, on lymphocyte protein synthesis in vitro. At a concentration of 7.5 × 10^?6M, levamisole stimulation resulted in a maximal increase in protein synthesis of 136% of control. Levamisole caused no increase in protein synthesis of “T-cell depleted” populations but increased protein synthesis of “T-cell enriched” populations to a degree greater than that observed with whole lymphocyte populations. These results demonstrate that levamisole increases lymphocyte protein synthesis and suggest that the increase is due to selective stimulation of T-cells. These results provide an explanation for the effects of levamisole on lymphokine production and E-rosette formation previously reported.     

Selective induction of B7/BB-1 on interferon-gamma stimulated monocytes: a potential mechanism for amplification of T cell activation through the CD28 pathway.

The B cell activation antigen B7/BB-1 is the natural ligand for the T cell antigen CD28 and these two molecules are capable of mediating T-B cell adhesion. Engagement of the CD28 pathway provides a costimulatory signal to T cells leading to enhanced lymphokine production. We report that interferon-gamma (INF-gamma) induces the expression of B7/BB-1 on monocytes. This induction was very specific since other cytokines and stimuli which activate monocytes including M-CSF, GM-CSF, IL3, TNF-alpha, and LPS were unable to induce B7/BB-1. Following culture of monocytes with INF-gamma, maximal mRNA and cell surface B7/BB-1 expression was detected at 12 and 24 hr, respectively. In addition to antigen presentation, optimal T cell activation and lymphokine synthesis require an additional cell to cell contact signal provided by the antigen presenting cell. The induction of B7/BB-1 on monocytes and subsequent heterophilic interaction of B7/BB-1 with CD28 may provide a mechanism for the amplification of T cell proliferation and lymphokine production by INF-gamma activated monocytes.     

Transient behavior of T-cell hybridomas in response to changes in metabolite concentrations in continuous culture.

Effects of pulse and step changes in major metabolite concentrations such as glucose, glutamine, lactic acid, and ammonium on behavior of T-cell hybridomas in continuous culture were investigated in order to develop a strategy to maximize specific rate of lymphokine formation. Step increases in glucose, lactic acid, and ammonium concentrations decreased, and a step increase in glutamine concentration increased, the specific rate of lymphokine formation. Effects of step and pulse changes on specific rates of glucose and glutamine consumption and viability of cells were also investigated.     

Surface features of Entamoeba histolytica and rabbit kidney (RK13) cell surface changes after trophozoite contact--observations by scanning electron microscopy.

Trophozoites of Entamoeba histolytica grown on glass, fixed in situ, and examined by scanning electron microscopy (SEM) were seen to possess microfilopodia on their lower sides and under surfaces, a hitherto undescribed feature. No surface lysosomes were seen. After trophozoites had been brought into contact with a host monolayer of cultured RK13 cells, immediate surface changes were observed. First the RK13 cell surface microvilli elongated, then decreased in number and finally disappeared. These changes were accompanied by erosion of the cell surface and cellular swelling.     

Cell surface receptors for lymphokines. II. Studies on the carbohydrate composition of the MIF receptor on macrophages using synthetic saccharides and plant lectins.

The carbohydrate composition of the surface receptor for macrophage migration inhibitory factor (MIF) on guinea pig macrophages has been studied by examining the interaction of MIF with different saccharides and by testing the ability of plant lectins with known saccharide binding affinities to bind to macrophages and block their response to MIF. Comparison of the effectiveness of a variety of natural and synthetic mono- and disaccharides in inhibiting MIF activity in lymphocyte supernatants revealed that inhibitory activity was confined to natural 5-methylpentose sugars (l-fucose > l-rhamnose = 6-deoxy-d-glucose) and synthetic saccharides containing α-fucosyl residues. Observations on the MIF inhibitory activity of synthetic fucosyl glycosides containing fucosyl residues of defined configuration at terminal and subterminal positions indicate that MIF interacts preferentially with terminal α-l-fucopyranosyl residues and does not recognize subterminal saccharides. Studies with disaccharides containing α-(1 → 2)-, α-(1 → 3), and α-(1 → 6)-linked l-fucosyl residues failed to reveal preferential interaction of MIF with any one linkage configuration. Incubation of macrophages before exposure to MIF with lectins that bind to terminal fucosyl residues (Lotus tetragonolobus and Ulex europaeus_I, agglutinins) rendered them unresponsive to MIF but lectins which bind to nonterminal fucosyl residues and to other saccharides had no effect. The role of fucosyl residues in the binding of MIF by macrophages is discussed with reference to the possible composition of the MIF receptor and the role of fucose-containing glycolipids as receptors for this lymphokine.     

Physiological Studies on Pea Tendrils: VII. Evaluation of a Technique for the Asymmetrical Application of Ethylene

A technique has been devised for the asymmetrical application of ethylene to specific surfaces of plant tissue. 2-Chloroethylphosphonic acid (CEPA) was dissolved in a phosphate buffer (pH 6.5) containing Tween-20 or dimethylsulfoxide as adjuvant. Ethylene evolution from tendrils of Pisum sativum cv. Alaska was greater during coiling than when they were at rest; and via topical application to the ventral surface, CEPA was able to stimulate contact coiling. Within 1 day of application of CEPA, the tendrils showed symptoms of senescence. It is concluded that ethylene participates in the control of contact coiling stimulated by touch, and it is suggested that this control may be exerted via permeability changes in the membranes of the motor cells.     

Studies on the mechanism of PMN activation III. by lymphokines

The influence of a guinea pig lymphokine preparation on the oxidative metabolism of human and guinea pig granulocytes of various sources was investigated. A dose-dependent increase of the oxidative burst following lymphokine challenge was observed. It occurred in unstimulated guinea pig peripheral polymorphonuclear leukocytes (PMN) and in prestimulated PMN obtained from the peritoneal cavity after glycogen injection as well. The lymphokine effect on the oxidative metabolism is not species-restricted because the guinea pig lymphokine preparation elicits an oxidative burst in human PMN, too. The increase caused by lymphokines is nearly of the same order of magnitude as that obtained with zymosan.     

Desensitization V: Suppression of MIF production by lymphokine-activated macrophages

The systemic injection of high doses of antigen into a previously immunized animal results in a state of transient anergy with respect to cell-mediated immune reactions. This phenomenon is known as desensitization. We have previously shown that desensitization is a multistage process. The initial 24-hr period is characterized by excessive lymphokine production with a failure to express delayed hypersensitivity reactions due to abolition of local chemotactic gradients. Subsequent stages of desensitization involve failure of lymphokine production in vivo. The results presented here demonstrate that lymphocytes obtained from immunized and desensitized animals later than 24 hr after desensitization are markedly suppressed in their ability to produce MIF. In addition, it was found that lymphokine-activated macrophages can suppress in vitro MIF production by lymphocytes from immune, nondesensitized animals. In vitro and in vivo activation of macrophages were equally effective. Thus, it is likely that at least one mechanism for the inhibition of lymphokine production in the post-24-hr period of desensitization, involves activation of a population of suppressor macrophages by lymphokines produced during the initial 24-hr period.     

IL-10 inhibits parasite killing and nitrogen oxide production by IFN-gamma-activated macrophages.

IL-10, a cytokine produced by CD4+ T lymphocytes belonging to the Th-2 subset, has previously been shown to inhibit the synthesis of IFN-gamma by both T cells and NK cells. We now demonstrate that IL-10 can also down-regulate IFN-gamma-dependent immunity by blocking the ability of that lymphokine to activate macrophages. Thus, IL-10, in a dose-dependent manner, inhibits the microbicidal activity of IFN-gamma-treated inflammatory macrophages against intracellular Toxoplasma gondii as well as the extracellular killing of schistosomula of Schistosoma mansoni. This suppression correlates with the inhibition by IL-10 of IFN-gamma-induced production of toxic nitrogen oxide metabolites, an effector mechanism previously implicated in the killing by macrophages of both parasite targets. IL-10 inhibition of nitric oxide production was shown to occur when the cytokine is given before or together with the IFN-gamma-activating stimulus, but not after its removal from the cultures and to require 12 h of contact for maximal suppressive effect on macrophage function. These results, taken together with previous findings on the down-regulation of Th1 lymphokine production by IL-10, indicate that the induction of IL-10 may be an important strategy by which parasites evade IFN-gamma-dependent, cell-mediated immune destruction.     

Cognate interactions between helper T cells and B cells. II. Dissection of cognate help by using a class II-restricted, antigen-specific, IL-2-dependent helper T cell clone

In order to determine the involvement of T-B cell contact vs lymphokine production in mediating B cell cycle entry and progression, Th cell clones "defective" in lymphokine production were cloned. Th-3.1 is one such clone that required IL-2 to produce significant levels of IL-4 and IFN-gamma. Unlike conventional Th clones, Th-3.1 induced B cell proliferation only in the presence of Ag and IL-2. In contrast to the absolute requirement of IL-2 for Th-3.1-induced B cell proliferation, IL-2 was not required for the formation of stable Th-3.1-B cell conjugates or Th-3.1-induced B cell entry into the G1 phase of the cell cycle. In the absence of IL-2 and under conditions that promoted Th-B cell interactions, Th-3.1 induced 10 to 20% of resting B cells to enter G1. B cell entry into the cell cycle was not inhibited by anti-lymphokine mAb or promoted by exogenous lymphokines, suggesting that endogenous lymphokine activity was not required for Th-3.1-induced G0 to G1 transition. The data suggested that the IL-2-independent induction of B cells into G1 by Th-3.1 was a cell contact-dependent event. Direct proof that Th-3.1-B cell contact was necessary for B cell cycle entry was provided by comparative in situ analysis of the RNA synthetic activity and the RNA content of B cells that were in physical contact with Th-3.1 or not in contact with Th-3.1. In situ autoradiography of RNA synthesis illustrated that a high frequency of B cells in contact with Th-3.1 expressed heightened RNA synthetic activity, whereas "bystander" B cells were less frequently induced into cycle. In situ laser cytometry of B cell size and total RNA content showed that B cells in physical contact with Th-3.1 had a higher RNA content and were larger than "bystander" B cells present in the same microcultures. This model system has allowed the dissection of T cell help into IL-2-dependent and IL-2-independent phases. Early cell contact-dependent events and B cell cycle progression into G1 were IL-2 independent, whereas the production of lymphokines (IL-4, IFN-gamma) by Th-3.1 and Th-3.1-induced B cell proliferation was IL-2 dependent.     

Lymphokine production in mouse mixed lymphocyte reaction (MLR)

We have investigated alloantigen differences which stimulate lymphokine release and³H-TdR uptake in primary ‘one-way’ MLC among allogeneic mice. When mice differing at the wholeH-2 region were tested, MIF and immune IF release was observed, along with a marked³H-TdR uptake. Differences atK, D, orI-S-G regions stimulate both lymphokine release and³H-TdR uptake, though stronger immune IF and³H-TdR responses were observed with differences atI-S-G regions. On the other hand, when mice differing in their minor histocompatibility antigens, and notably at theMls locus, were tested, lymphokine release took place even in the absence of proliferation. Lastly, in MLC between mice differing at multiple minor loci, butH-2 andMls matched, MIF release only, and not immune IF and³H-TdR responses were observed in a few combinations. These findings show that T lymphocytes can recognize alloantigens by releasing lymphokines even without going through proliferation. Moreover, different levels of T-lymphocyte activation exist, depending on the kind of stimulating alloantigens present.