Blood concentrations of interleukin-15 in cancer patients and their variations during interleukin-2 immunotherapy: preliminary considerations

In addition to the better known cytokines IL-2 and IL-12, IL-15, which is mainly produced by macrophages, is a new antitumor cytokine with a mechanism of action similar to that of IL-2. At present, however, there are no data about IL-15 secretion in cancer patients. This study was carried out to evaluate IL-15 blood concentrations in patients with early or advanced cancer and their possible variations in response to IL-2 cancer immunotherapy. The study included 40 patients with solid tumors, 24 of whom had metastatic disease. In addition, IL-15 secretion was evaluated during subcutaneous low-dose IL-2 therapy (6 million IU/day for 6 days/week for 4 weeks) in 14 metastatic renal cell cancer patients by collecting blood samples at weekly intervals. The control group consisted of 40 age-matched healthy subjects. Serum levels of IL-15 were measured by an enzyme immunoassay. No significant difference in mean serum levels of IL-15 was observed between cancer patients and controls. Moreover, the mean serum levels of IL-15 found in metastatic cancer patients were not significantly different from those found in patients with limited disease. Finally, no significant changes in mean levels of IL-15 occurred during IL-2 cancer immunotherapy. This preliminary study would suggest that IL-15 secretion is substantially within the normal range in cancer patients, both in early and advanced disease, and no variation seems to occur in response to IL-2 administration.     

Abrogation of surgery-induced IL-6 hypersecretion by presurgical immunotherapy with IL-2 and its importance in the prevention of postoperative complications

Because of its immunosuppressive effect, surgery-induced immunosuppression may depend at least in part on the postoperative hypersecretion of IL-6, which is also responsible for surgical complications. Most of the immunosuppressive events induced by surgery, including lymphocytopenia, NK and T lymphocyte decline, and dendritic cell deficiency have been proven to be abrogated by a preoperative injection of IL-2 for few days. However, the cytokine mechanisms responsible for IL-2-induced abrogation of surgery-related immunosuppression need to be better investigated and understood. This study was performed to analyze the influence of IL-2 presurgical immunotherapy on IL-6 secretion in the postoperative period. The study was performed in 12 operable colorectal cancer patients, who were preoperatively pretreated with IL-2 (12 million lU/day subcutaneously for 3 consecutive days before surgery). The control group consisted of 21 age-and disease-matched colorectal cancer patients who underwent surgery without a preoperative immunotherapy with IL-2. Serum levels of IL-6 were measured by an enzyme immunoassay before surgery, and at days 3 and 7 of the postoperative period. A significant increase in mean serum levels of IL-6 occurred in the postoperative period only in the control patients, whereas in the IL-2 pretreated group no significant difference was seen between presurgical and postoperative IL-6 mean concentrations. The difference between controls and IL-2 group was particularly evident for patients with abnormally elevated presurgical values of IL-6. This study, by showing that a presurgical injection of IL-2 may prevent surgery-induced IL-6 enhanced secretion, would suggest that the previously described neutralization of surgery-induced immunosuppression by IL-2 preoperative immunotherapy may depend at least in part on the inhibition of postoperative production of IL-6, whose immunosuppressive effects have been well demonstrated at least on anticancer immunity.     

Elevated circulating levels of soluble interleukin-1 receptor type II during interleukin-2 immunotherapy

Interleukin-1 (IL-1) is a critical mediator of inflammation. Two naturally occurring IL-1 antagonists have been described, namely the IL-1 receptor antagonist (IL-1Ra) and the IL-1 receptor type II (IL-1RII). IL-1RII does not transmit a signal upon binding of IL-1, but competes with the signaling of IL-1RI for binding of IL-1. Shedding of IL-1RII yields the soluble IL-1 receptor type II (IL-1sRII) which retains the ability of membrane-bound IL-1RII to bind IL-1beta avidly, but binds IL-1Ra and IL-1alpha with low affinity. In contrast, IL-1sRI retains the ability of membrane-bound IL-1RI to bind IL-1Ra and IL-1alpha with high affinity, but binds IL-1beta poorly. We have previously shown that immunotherapy with IL-2 or IL-6 in cancer patients is associated with a dramatic increase in IL-1Ra plasma levels. In the present study, plasma levels of soluble IL-1 receptors were monitored in healthy individuals and cancer patients. In healthy controls, the mean IL-1sRII level was 4.76 0.16 ng/ml. IL-1sRII levels in cancer patients were comparable to those measured in healthy controls. IL-1sRII levels did not vary during the first 52 hours after initiation of IL-2 therapy, but increased significantly thereafter to reach 9.56 1.16 ng/ml on day 5. In contrast, IL-6 immunotherapy with a 5-day continuous infusion did not trigger an increase in IL-1sRII levels. IL-1sRI levels did not increase during immunotherapy with IL-2 or IL-6. Our results indicate that IL-1sRII, unlike IL-1Ra, remains a modest, natural, anti-inflammatory mechanism triggered by immunotherapy with IL-2, but not with IL-6.     

Cortisol response to an acute injection of IL-2 in healthy subjects and cancer patients: a first immunoneuroendocrine standardized clinical test to explore the interactions between immune and neuroendocrine systems

Preliminary clinical studies would suggest that the immune alterations characterizing severe human illnesses, such as autoimmune diseases and cancer itself, may depend at least in part on an anomalous psychoneuroendocrine regulation of the immunity. Unfortunately, at present the psychoneuroimmune interactions may be clinically investigated only by separately analyzing the neuroendocrine and the immune systems, since there is no standardized clinical test capable of detecting the physiological response of the endocrine secretion to an immune stimulation. One of the main endocrine functions influenced by the immune activation is the hypothalamic-pituitary-adrenal axis. In fact, several cytokines have appeared to stimulate cortisol secretion by acting at a central site. On this basis, a study was planned to evaluate cortisol response to an acute IL-2 injection in healthy subjects and metastatic cancer patients, in an attempt to standardize a clinical neuroendocrinoimmune test capable of documenting possible alterations of the link between neuroendocrine and immune systems. The study included 10 healthy subjects as a control group and 10 cancer patients with metastatic disease. Control subjects were evaluated in basal conditions to determine the physiological circadian rhythm of cortisol, and after the subcutaneous (SC) injection of IL-2 (3 and 9 million IU). IL-2 at 3 million IU stimulated cortisol release in all healthy controls and in none of the cancer patients. IL-2 at 9 million IU induced a significant increase in cortisol mean levels in cancer patients, whose values, however, were still significantly lower with respect to those seen in controls in response to IL-2 at 3 million IU. No important IL-2 related side-effect occurred. This study shows that an acute SC injection of low-dose IL-2 with a following evaluation of cortisol secretion may constitute a first standardized immunoendocrine test, capable of exploring the status of the physiological link between neuroendocrine and immune systems, and of documenting the existence of important alterations in human diseases related to an immune dysfunction, such as advanced cancer, which has appeared to be characterized by a hyposensitivity of the hypothalamic-pituitary-adrenal axis to an acute cytokine administration.     

Activation of the complement system during immunotherapy of cancer with interleukin-2: a possible explanation of the capillary leak syndrome

The capillary leak syndrome, responsible for fluid loss into the interstitial space, represents one of the major cardiovascular toxicities of IL-2 during the immunotherapy of cancer. The mechanisms involved in the increased vascular permeability have still to be better understood. The present study was carried out to investigate the role of the complement system in mediating the IL-2 vascular toxicity. The study was performed in metastatic renal cancer patients, treated with IL-2 through a 24-hour i.v. infusion at a daily dose of 3 x 10(6) U/m2 for 5 consecutive days, corresponding to one IL-2 course. Six IL-2 courses were evaluated. C3 and C4 were measured daily during IL-2 infusion, and 2 and 5 days after its interruption. IL-2 administration induced a significant decrease in both C3 and C4 mean levels, which became within the normal range 5 days after the end of IL-2 infusion. These results show that IL-2 administration may directly activate the complement system through the classical pathway, which might play a role in determining the increased vascular permeability.     

Interleukin-2 and interleukin-15: immunotherapy for cancer

Interleukin (IL)-2 and IL-15 are two cytokine growth factors that regulate lymphocyte function and homeostasis. Early clinical interest in the use of IL-2 in the immunotherapy of renal cell carcinoma and malignant melanoma demonstrated the first efficacy for cytokine monotherapy in the treatment of neoplastic disease. Advances in our understanding of the cellular and molecular biology of IL-2 and its receptor complex have provided rationale to better utilize IL-2 to expand and activate immune effectors in patients with cancer. Exciting new developments in monoclonal antibodies recognizing tumor targets and tumor vaccines have provided new avenues to combine with IL-2 therapy in cancer patients. IL-15, initially thought to mediate similar biological effects as IL-2, has been shown to have unique properties in basic and pre-clinical studies that may be of benefit in the immunotherapy of cancer. This review first summarizes the differences between IL-2 and IL-15 and highlights that better understanding of normal physiology creates new ideas for the immunotherapy of cancer. The application of high, intermediate, and low/ultra low dose IL-2 therapy in clinical trials of cancer patients is discussed, along with new avenues for its use in neoplastic diseases. The growing basic and pre-clinical evidence demonstrating that IL-15 may be useful in immunotherapy approaches to cancer is also presented.     

Endocrine effects of human recombinant interleukin-3 in cancer patients.

It is known that several cytokines can exert hormonal effects. At present, no data are available about the possible influence of IL-3 on the endocrine system. In order to investigate the endocrine effects of IL-3 in humans, we have evaluated serum levels of cortisol, beta-endorphin, GH, PRL, FSH, LH, TSH and melatonin in response to intravenous injection of IL-3 at a dose of 1 mcg/kg b.w. at 6.00 p.m. The study was performed in 5 non-small cell lung cancer patients. GH increased significantly in response to IL-3. PRL showed a progressive decrease after IL-3 injection, but its variations were not statistically significant. All other hormones, including cortisol, were not affected by IL-3. This preliminary study shows that IL-3 may exert endocrine effects in humans, which would seem at variance with previously reported results on most other cytokines.     

Contribution of interleukin-1 receptor accessory protein B to interleukin-1 actions in neuronal cells

Interleukin (IL)-1 is an important neuroimmunomodulator and a key mediator of inflammation during brain disorders. It acts on neuronal and glial cells via binding to the IL-1 type 1 receptor and IL-1 receptor accessory protein (IL-1RAcP). More recently, a neuronal-specific isoform of IL-1RAcP, named IL-1RAcPb, has been identified. Our aim was to determine the role of IL-1RAcPb in IL-1 actions in neuronal and glial cells, and to further explore the signaling mechanisms of IL-1 in neurons. We found that IL-1RAcPb deletion had no effect on IL-1α- and IL-1β-induced activation of the extracellular signal-regulated kinase 1/2 or IL-6 release in glial cultures, although IL-6 release in response to high IL-1α concentration (30 IU/ml) was significantly reduced. We identified the p38 kinase as a key signaling element in IL-1α- and IL-1β-induced IL-6 synthesis and release in neuronal cultures. IL-1RAcPb deletion had no effect on IL-1α- and IL-1β-induced IL-6 release in neurons, but significantly reduced IL-1α- but not IL-1β-induced p38 phosphorylation. Our data demonstrate that the p38 signaling pathway plays an important role in IL-1 actions in neurons, and that IL-1RAcP may regulate some, but not all, neuronal activities in response to IL-1α.     

Tiludronate inhibits interleukin-6 synthesis in osteoblasts: Inhibition of phospholipase D activation in MC3T3-E1 cells

In previous studies, we have reported that PGF_2α stimulates phosphoinositide hydrolysis by phospholipase C and phosphatidylcholine hydrolysis by phospholipase D through heterotrimeric GTP-binding protein in osteoblast-like MC3T3-E1 cells, and that PGF_2α and PGE₁ induce interleukin-6 (IL-6) synthesis via activation of protein kinase C and protein kinase A, respectively. In the present study, we investigated the effect of tiludronate, a bisphosphonate known to inhibit bone resorption, on the PGF_2α- and PGE₁-induced IL-6 synthesis in these cells. Tiludronate significantly suppressed the PGF_2α-induced IL-6 secretion in a dose-dependent manner in the range between 0.1 and 30 μM. However, the IL-6 secretion induced by PGE₁ or (Bu)₂cAMP was hardly affected by tiludronate. The choline formation induced by PGF_2α was reduced by tiludronate dose-dependently in the range between 0.1 and 30 μM. On the contrary, tiludronate had no effect on PGF_2α-induced formation of inositol phosphates. Tiludronate suppressed the choline formation induced by NaF, known as an activator of heterotrimeric GTP-binding protein. However, tiludronate had little effect on the formation of choline induced by TPA, a protein kinase C activator. Tiludronate significantly inhibited the NaF-induced IL-6 secretion in human osteoblastic osteosarcoma Saos-2 cells. These results strongly suggest that tiludronate inhibits PGF_2α-induced IL-6 synthesis via suppression of phosphatidylcholine-hydrolyzing phospholipase D activation in osteoblasts, and that the inhibitory effect is exerted at the point between heterotrimeric GTP-binding protein and phospholipase D. J. Cell. Biochem. 69:252–259, 1998. © 1998 Wiley-Liss, Inc.     

Immunological effects of a single evening subcutaneous injection of low-dose interleukin-2 in association with the pineal hormone melatonin in advanced cancer patients.

Recent experiments have shown that a great variety of neurohormones can interact with IL-2 in the modulation of host antitumor immune response. On the basis of these data, a study was started to evaluate the effect of the pineal hormone melatonin (MLT) on IL-2-induced immune changes in cancer. The study included 30 advanced cancer patients. They were randomized to be treated with IL-2 at a dose of 3 million IU subcutaneously twice/daily (8.00 a.m. and 8.00 p.m.) for 6 days/week for 4 weeks, with IL-2 once/daily in the evening, with IL-2 once/daily plus MLT at 10 or at 50 mg/day. MLT was given orally at 8.00 p.m. Both IL-2 given twice daily and IL-2 given once daily and IL-2 given once daily in association with MTL induced a significant increase in mean number of lymphocytes, T lymphocytes, NK cells, CD25-positive cells and eosinophils, whereas the single administration of IL-2 alone was unable to determine a significant rise in the mean number of immune cells. Soluble IL-2 receptor and neopterin increase was significantly higher during IL-2 given twice/daily than during IL-2 plus MLT, while no difference was seen in TNF rise. This study would suggest that a single daily injection of low-dose IL-2 is able to efficiently activate the lymphocyte proliferation in cancer patients when it is given in association with the pineal hormone MLT.     

Stimulation of interleukin-6 release by interleukin-1beta from isolated human adipocytes

The secretion of interleukin-6 (IL-6) is modulated by immune, hormonal and metabolic stimuli in a cell-specific manner. We investigated the effect of cytokines, TNFalpha and IL-1beta, and insulin on IL-6 release from human adipocytes and peripheral blood cells (PBC). Adipocytes released IL-6 constitutively (after 5 h: 5.64 [1.61-15.30]pg ml(-1), after 10 h: 15.95 [2.34-45.59]pg ml(-1), p = 0.007), while PBC secretion did not change significantly over this period. LPS stimulated IL-6 secretion in PBC after 5 h but was without effect on adipocytes. TNFalpha and insulin induced IL-6 production from PBC, but had no effect on adipocytes. IL-1beta, however, induced a substantial increase in IL-6 release in adipocytes and PBC (all p < 0.05). Adipose tissue production of IL-1beta was assessed in vivo by measuring arterio-venous differences across the subcutaneous abdominal adipose bed. Net release of IL-1beta was not observed, suggesting that under basal conditions there is no detectable release of this cytokine into the circulation from this depot. In conclusion (1) PBC demonstrate regulated IL-6 release, while the adipocyte release has a large constitutive component; (2) immune modulators, such as LPS, TNFalpha and IL-1beta, all induce PBC IL-6 release, but only IL-1beta stimulates adipocyte release. Though IL-1beta is not an endocrine signal from adipose tissue, it is an autocrine/paracrine stimulator of IL-6 release from human adipocytes.     

Induction of natural killer cell activity and perforin and granzyme B gene expression following continuous culture of short pulse with interleukin-12 in young and old mice

Anticancer immunotherapy with cytokines is often limited by the occurrence of severe toxicity, particularly in older age groups, which are characterized by a reduced tolerance to antineoplastic therapies. We, and others, have recently demonstrated the efficacy of pulsing procedures with IL-2 as a new therapeutic strategy to induce antitumor cytotoxic cells. The aim of this paper was to evaluate the effect of IL-12 on NK cell activity in young and old mice and to investigate the possibility of inducing NK cytotoxicity and perforin and granzyme B gene expression through a brief exposure of spleen lymphocytes from young and old mice to IL-12. Pulsed lymphocytes were compared with non-pulsed cells cultured continuously in IL-12. IL-12 was able to boost both endogenous and IL-2-induced NK cell activity in young and old mice; the levels of cytotoxicity were lower in old than in young animals although the relative increase of IL-12 plus IL-2 versus IL-2 alone was greater for old mice. Comparable levels of NK cell activity were obtained in pulsed (5 min-1 hour) and non-pulsed lymphocytes from both young and old mice after one or three days of culture. The efficacy of the pulsing procedure was evident in both endogenous and IL-2-induced NK cytotoxicity. The mRNA encoding perforin and granzyme B were markedly and similarly enhanced in both IL-12-pulsed and non-pulsed lymphocytes in comparison with control cells. The results demonstrate the effectiveness of IL-12 pulsing in inducing antitumor cytotoxic cells, suggesting the possibility of using IL-12 pulsing, alone or in combination with IL-2, in the immunotherapy of both young and old subjects.     

Importance in timing of cyclophosphamide on the enhancement of interleukin-2-induced cytolysis

Summary We investigated the in vivo effects of cyclophosphamide (CY) on interleukin-2(IL-2)-induced cytolytic function and spleen cell immunophenotype. Pretreatment of A/J mice with CY (25 mg/kg or 75 mg/kg) i.p. on days –10 and –15 followed by IL-2 (50 000 U i.p. on days 0 to +3) resulted in increased lysis of YAC-1 target cells compared to the group receiving IL-2 without previous CY therapy. In contrast, when CY was given on day -5, the cytotoxicity against YAC-1 was not enhanced. Phenotypic analysis of splenocytes obtained from mice treated with CY on day –10 or –15 revealed a relative decrease in L3T4- and Lyt2-positive T cells. In vivo depletion of natural killer (NK) cells by anti-asialoG_M1, prior to IL-2 therapy, abrogated the enhancing effect of CY on cytolysis while in vivo elimination of T cells by anti-L3T4 and anti-Lyt2 monoclonal antibodies did not, indicating that in the absence of T cell antigenic challenge, the increased cytolytic function after CY administration is probably mediated through NK cells. These findings provide evidence that CY may be used more effectively in IL-2-based immunotherapy protocols, if consideration is given to timing of CY and IL-2 administration.Supported in part by the Children's Cancer Research Fund, the Concern II Foundation, RO1-CA-21 737, NO1-AI-85 002 and a contract to the University of Minnesota from OncoTherapeutics Inc. Dr. E. Katsanis is supported by a fellowship from the Medical Research Council of Canada. Dr. P. M. Anderson is supported by a Clinical Oncology Career Development Award from the American Cancer Society. This is paper no. 550 of the Immunobiology Research Center     

Role of interleukin-15 and interleukin-18 in the secretion of sIL-6R and sgp130 by human neutrophils

BACKGROUND: Available data indicate that neutrophils (PMN) produce a wide range of cytokines with the potential to modulate immune response. Recent investigation have shown that interleukin (IL)-15 and IL-18 potentiated several functions of normal neutrophils. It has been reported that IL-18-induced cytokine production may be significantly enhanced by coincident addition of IL-15. AIMS: In the present study we compared the effect of recombinant human (rh)IL-15 and rhIL-18 as well as effect of a rhIL-15 and rhIL-18 combination on the induction secretion of sIL-6Ralpha and sgp130 by human neutrophils. METHODS: PMN were isolated from heparinized whole blood of healthy persons. The PMN were cultured for 18 h at 37 degrees C in a humidified incubator with 5% CO(2). rhIL-15 and/or rhIL-18 and lipopolysaccharide were tested to PMN stimulation. The culture supernatants of PMN were removed and examined for the presence of sIL-6R and sgp130 by human enzyme-linked immunosorbent assay kits. Cytoplasmic protein fractions of PMN were analysed for the presence of sIL-6R and sgp130 by western blotting using monoclonal antibodies capable of detecting these proteins. Cells were lysed and cytoplasmic proteins were electrophoresed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The resolved proteins were transferred onto nitrocellulose and incubated with the primary monoclonal antibodies anti-sIL-6R and anti-sgp130. The membranes were incubated at room temperature with alkaline phosphatase anti-mouse immunoglobulin G. Immunoreactive protein bans were visualized by an AP Conjugate Substrate Kit. RESULTS AND CONCLUSIONS: The results of our investigation revealed that IL-15 alone, similarly to IL-18, has no significant ability for the regulation of both soluble IL-6 receptors, sIL-6R and sgp130, released by human neutrophils. It is interesting to note that the secretion of sgp130 was changed after PMN stimulation with rhIL-15 in the presence of rhIL-18. The combination of rhIL-15 and rhIL-18 was shown to induce PMN to secretion relatively higher amounts of sgp130 compared with the stimulation of PMN with rhIL-15 alone and rhIL-18 alone. The results obtained suggest that IL-15 and IL-18, belonging to the inflammatory cytokines, through the regulation of sgp130 secretion must be also considered as anti-inflammatory mediators that may influence the balance reactions mediated by the IL-6 cytokine family.     

Lymphokine release, suppressor cell generation, cell surface markers, and cytotoxic activity in cancer patients receiving natural interleukin-2

We monitored patients treated for 5 days with continuous infusion of increasing doses (3 to 6 x 10(6) U/d) of natural interleukin-2 (IL-2). CD16+, CD25+, and CD56+ cells increased after treatment. Plasma tumor necrosis factor-alpha (TNF-alpha) levels, but not interferon-gamma (IFN-gamma) levels, increased during IL-2 treatment, but spontaneous and IL-2-stimulated TNF-alpha secretion in vitro remained abnormally low. However, mitogen-stimulated TNF-alpha release was normal. Mitogen-stimulated, but not IL-2-stimulated, IFN-gamma release was strongly depressed. Low spontaneous and IL-2-stimulated cytotoxicity on K562 or Daudi increased after treatment. Low suppressor cell generation also normalized after treatment. This appears to be the first reported study of immunologic monitoring of cancer patients treated with natural rather than recombinant IL-2.     

Cryopreservation-induced enhancement of interleukin-2 production in human peripheral blood mononuclear cells.

To better understand the effects of cryopreservation on various immunocompetent cell functions, we have examined the interleukin-2 (IL-2)-producing activities of frozen mononuclear cells (MNCs) from healthy subjects. The mechanisms responsible for the observed effects were also analyzed. Both the unfractionated and monocyte-depleted, frozen MNCs produced significantly larger quantities of IL-2 than fresh cells. Similar to freezing, L-leucine methyl ester (Leu-OMe) treatment (to eliminate IL-1 and prostaglandin E-2 (PGE-2)-secreting cells) also increased the IL-2-producing activities of fresh cells, but freezing no longer enhanced the production of IL-2 by Leu-OMe-treated cells, suggesting that (1) both the freezing process and Leu-OMe treatment have similar effects on IL-2 production, (2) the increased IL-2 secretion by frozen MNCs is independent of IL-1, and (3) inactivation of PGE-2-secreting cells during the freezing procedure is responsible for increased IL-2 secretion. Elimination of CD8+ T cells (putative suppressor cells) from MNCs has also resulted in the production of increased amounts of IL-2 by fresh cells, and again, freezing did not further enhance the IL-2-secreting activities of MNCs, that are devoid of CD8+ T cells. This confirms that the increased IL-2 production is due to the inactivation of immuno-down-regulatory cells. The results provide further evidence that the lack of active, suppressor T cells, monocytes, and increased IL-1 and -2 production may be responsible for the previously reported enhanced immunoglobulin-producing abilities of cryopreserved cells from healthy subjects and from patients with lung cancer.     

Physiological mechanisms contributing to increased interleukin-1 secretion

Interleukin-1 (IL-1) is a monocyte-derived polypeptide that mediates many host defense adaptations to environmental and infectious stresses. This investigation was intended to characterize further IL-1 activity found in human plasma following exercise (3) and to identify physiological initiators of IL-1 secretion. IL-1 activity was measured by the ability of plasma fractions to stimulate lymphocyte proliferation. This activity appeared in plasma several hours after exercise on a cycle ergometer (1 h at 60% of aerobic capacity, n = 8 subjects) and was neutralized with a specific antiserum to human IL-1. The hypothesis that IL-1 release from monocytes was initiated by phagocytosis of material from cells damaged by exercise was tested. The increase in IL-1 activity did not correlate significantly (r = 0.55) with creatine kinase activity, a marker for release of intracellular proteins into the circulation, and IL-1 secretion by monocytes was not stimulated by incubation with red blood cell lysates in vitro. Thus the stimulus for IL-1 secretion did not appear to be related to a scavenging function of monocytes. The possibility that IL-1 secretion may be mediated by stress hormones associated with exercise was examined. IL-1 secretion by monocytes was increased up to 48 +/- 18% (P less than 0.01) by addition of physiological concentrations of epinephrine in vitro. Low concentrations of hydrocortisone (1 ng/ml) also augmented IL-1 secretion by 58 +/- 20%. Higher concentrations in the physiological range had no effect, and combinations of epinephrine and hydrocortisone suppressed IL-1 secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modification of biological responses to interleukin-1 by agents that perturb signal transduction pathways.

In this study we have examined the effect of agents known to perturb certain signal transduction pathways on the biological responses of target cells to stimulation with interleukin-1 (IL-1). In the murine thymoma cell line EL4, IL-1 stimulation results in the secretion of interleukin-2 (IL-2), which was subsequently measured by proliferation of an IL-2-dependent cell line. Agents that elevated intracellular cAMP blocked or partially blocked IL-1 induction of IL-2 secretion, whereas agents that activated protein kinase C (PKC) resulted in a synergistic enhancement. Both pertussis and cholera toxins also inhibited IL-1-induced IL-2 secretion, although probably by acting at different levels. IL-1 simulation of human and murine fibroblasts resulted in release of prostaglandin E2. This response was inhibitable by pertussis toxin but not by cholera toxin, whereas co-stimulation of the fibroblasts with IL-1 and phorbol ester resulted in a synergistic response. Murine fibroblasts could also be stimulated to proliferate by IL-1, and this response was also inhibitable by pertussis toxin. These findings are consistent with coupling of the IL-1 receptor to a signalling pathway via a pertussis toxin substrate.