Interleukin-8 in sepsis: relation to shock and inflammatory mediators

Because of its neutrophil-activating properties, interleukin-8 (IL-8) may play an important role in the pathophysiology of sepsis. We measured circulating IL-8 levels in 47 patients with clinical sepsis. Levels on admission were elevated in 42 of the 47 patients (89%) and were comparable in patients with gram-positive or gram-negative infections. Patients with shock had significantly higher IL-8 levels than normotensive patients (P = 0.0014, Wilcoxon-Mann-Whitney test), whereas no differences in IL-8 levels were found between patients with or without adult respiratory distress syndrome. Patients who died had higher IL-8 levels on admission than the patients who survived. The largest differences in IL-8 levels between survivors and nonsurvivors was found when only patients with positive cultures were considered (P = 0.0342). IL-8 levels appeared to correlate significantly with lactate levels and inversely with leukocyte and platelet numbers and mean arterial pressure. In addition, the IL-8 level in the sepsis patients was found to correlate significantly with levels of IL-6, elastase-alpha 1-antitrypsin, and C3a. Serial observations revealed that in most patients IL-8 levels decreased, irrespective of the outcome. Thus, our results demonstrate that IL-8 levels are increased in most patients with sepsis and correlate with some important clinical, biochemical, and inflammatory parameters. These findings suggest a role for IL-8 in the pathophysiology of sepsis.

Interleukin-6 release and the acute-phase reaction in patients with acute myocardial infarction: a pilot study

We investigated the potential role of interleukin-6 as a mediator of the acute-phase reaction (APR) in patients with acute myocardial infarction. Of the six patients studied, five demonstrated increased plasma interleukin-6 levels. Interleukin-6 levels began to increase at 14 hours (mean; range = 8 to 20 hours) after the initial complaints and reached maximal levels of 28 to 250 U/mL (normal values less than 10 U/mL) after 36 hours (mean; range = 24 to 52 hours). No correlation was seen between the size of the interfaction as indicated by creatine kinase MB assays and the extent of the interleukin-6 increases (r = 0.44; p = 0.38). As an indicator of the APR, plasma C-reactive protein (CRP) levels were measured. CRP levels began to increase after 16 hours (mean; range = 8 to 24 hours) and reached maximum levels of 56 to 322 mg/L (normal values less than 3 mg/L) after 65 hours (mean; range = 48 to 92 hours). The increase of the interleukin-6 level preceded the increase of the CRP level in three patients and was simultaneous in two patients. Maximal interleukin-6 levels correlated significantly with maximal CRP levels (r = 0.96; p = 0.002). Thus these findings indicate that interleukin-6 is an important endogenous mediator for the APR in patients with acute myocardial infarction.

Characterization of IgG FcR-mediated proliferation of human T cells induced by mouse and human anti-CD3 monoclonal antibodies. Identification of a functional polymorphism to human IgG2 anti-CD3

T cell activation induced by mouse anti-CD3 mAb has shown to be dependent on the Ig isotype of these antibodies. A study of isotype dependency of human antibodies, however, seems more relevant to human effector systems, especially in view of the availability of humanized antibodies for clinical applications. We constructed a panel of mouse and mouse/human chimeric anti-CD3 mAb, which differ only in their CH region and hence have identical binding sites and affinity. By using these antibodies, we now studied their ability to induce T cell proliferation in human PBMC and analyzed the classes of IgG FcR involved in these responses. The human (h)IgG1, hIgG3, and hIgG4, as well as mouse (m)IgG2a and mIgG3 anti-CD3 mAb induced an Fc gamma RI (CD64)-dependent T cell proliferation in all donors. Activation with hIgG2 and mIgG1 anti-CD3 mAb was observed to be mediated via the low affinity Fc gamma RII (CD32). It was found that leukocytes in a normal donor population display a functional polymorphism with respect to hIgG2 anti-CD3 responsiveness. This polymorphism was found to be inversely related to the previously defined Fc gamma RII-polymorphism to mIgG1 anti-CD3 mAb. Monocytes expressing the Fc gamma RII mIgG1 low responder (LR) allele support hIgG2 anti-CD3 induced T cell proliferation efficiently, whereas cells homozygous for the Fc gamma RII mIgG1 high responder (HR) allele do not. This observation could be confirmed in T cell activation studies using hFc gamma RIIa-transfected mouse fibroblasts, expressing either the mIgG1 anti-CD3 HR or LR Fc gamma RII-encoding cDNA.

Characterization of IgG FcR-mediated proliferation of human T cells induced by mouse and human anti-CD3 monoclonal antibodies. Identification of a functional polymorphism to human IgG2 anti-CD3

T cell activation induced by mouse anti-CD3 mAb has shown to be dependent on the Ig isotype of these antibodies. A study of isotype dependency of human antibodies, however, seems more relevant to human effector systems, especially in view of the availability of humanized antibodies for clinical applications. We constructed a panel of mouse and mouse/human chimeric anti-CD3 mAb, which differ only in their CH region and hence have identical binding sites and affinity. By using these antibodies, we now studied their ability to induce T cell proliferation in human PBMC and analyzed the classes of IgG FcR involved in these responses. The human (h)IgG1, hIgG3, and hIgG4, as well as mouse (m)IgG2a and mIgG3 anti-CD3 mAb induced an Fc gamma RI (CD64)-dependent T cell proliferation in all donors. Activation with hIgG2 and mIgG1 anti-CD3 mAb was observed to be mediated via the low affinity Fc gamma RII (CD32). It was found that leukocytes in a normal donor population display a functional polymorphism with respect to hIgG2 anti-CD3 responsiveness. This polymorphism was found to be inversely related to the previously defined Fc gamma RII-polymorphism to mIgG1 anti-CD3 mAb. Monocytes expressing the Fc gamma RII mIgG1 low responder (LR) allele support hIgG2 anti-CD3 induced T cell proliferation efficiently, whereas cells homozygous for the Fc gamma RII mIgG1 high responder (HR) allele do not. This observation could be confirmed in T cell activation studies using hFc gamma RIIa-transfected mouse fibroblasts, expressing either the mIgG1 anti-CD3 HR or LR Fc gamma RII-encoding cDNA.

Effects on leukocytes after injection of tumor necrosis factor into healthy humans

Tumor necrosis factor (TNF) has been implicated as a proximal mediator of the septic syndrome. To evaluate the possible role of TNF in leukocyte activation in septicemia, we performed a cross-over saline-controlled study in six healthy men who were intravenously injected with recombinant human TNF (50 micrograms/m2), and analyzed changes in circulating white blood cells and parameters for neutrophil and monocyte activation. TNF elicited a very rapid neutropenia, reaching a nadir after 15 minutes, followed by a neutrophilia. Lymphocytes showed a sustained decrease, whereas monocytes declined transiently. TNF injection was also associated with neutrophil activation, as reflected by a mean fivefold increase in the plasma concentrations of elastase-alpha 1-antitrypsin complexes and a mean sevenfold increase in plasma lactoferrin levels. Serum neopterin, a marker of monocyte activation, was significantly increased 24 hours after the administration of TNF. These changes occurred in the absence of detectable complement activation, as indicated by unchanged C3a-desarg plasma values. Serum interleukin-6 showed a nearly 40-fold increase after TNF injection, whereas interleukin-1 remained undetectable throughout. We conclude that the systemic release of TNF, triggered early after invasive infection, may be involved in the alterations in circulating leukocyte numbers and in the activation of leukocytes, during the development of the septic syndrome.

Induction of urinary interleukin-1 (IL-1), IL-2, IL-6, and tumour necrosis factor during intravesical immunotherapy with bacillus Calmette-Guérin in superficial bladder cancer

To study the local immunological effects of intravesical bacillus Calmette-Guérin (BCG) therapy in superficial bladder cancer patients, the production of interleukin-1 (IL-1), IL-2, IL-6, tumour necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) was investigated in the urine. Urine specimens were collected during the six weekly BCG instillations, before instillation, and 2, 4, 6, 8, and 24 h thereafter. Results were standardized to urine creatinine. In general, the concentration of IL-1 increased markedly during the first three BCG instillations, reaching a plateau from instillations 3 to 6. IL-2 was not detected after the first BCG instillation, but from the second instillation onwards the mean IL-2 concentration increased rapidly. With respect to IL-6, patients had relatively high levels in the urine after the first BCG instillation. A relatively moderate increase of the IL-6 concentration was observed during the following weeks. Like IL-2, TNF alpha was only detected after repeated BCG instillations. Generally the highest TNF levels were found after BCG instillation 5. The presence of IFN gamma could not be demonstrated. With respect to the occurrence of the cytokines during the first 24 h after the BCG instillation, TNF, IL-2, and IL-6 were detectable 2 h after the instillation. In contrast, IL-1 seemed to appear later, i.e. from 4 h onwards. TNF decreased most rapidly; it was nearly absent in 6-h samples. Generally IL-2 was not detectable in the 8-h samples, whereas IL-1 and IL-6 were present up to 8 h after instillation of BCG. The presence of TNF was found less frequently than the presence of IL-1, IL-2, and IL-6. Neutralization experiments indicated that most of the IL-1 present in the urine after BCG treatment was IL-1 alpha. In conclusion, activation of BCG-specific T cells was indicated by the detection of IL-2. The presence of IL-1, IL-6, and TNF alpha might suggest activation of macrophages by intravesically administered BCG, although production by other cell types cannot be excluded. It is suggested that these cytokines, in combination with the leucocytes that are known to be recruited to the bladder in reaction to the BCG treatment, may play an important role in the antitumour activity of BCG against bladder cancer. For monitoring purposes, collection of urine might be performed during the first 6 h after BCG instillations 4-6.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of T-cell proliferation by recombinant mouse and chimeric mouse/human anti-CD3 monoclonal antibodies

The isotype of anti-CD3 mAb has a dramatic effect on anti-CD3 induced T-cell activation, as was previously reported for switch variants (IgG2b to IgA) of a high-avidity IgG1 anti-CD3 mAb (CLB-T3/4.1). In order to study and compare the isotype dependency of T-cell activation with anti-CD3 mAb of various mouse and human subclasses, we now prepared recombinant anti-CD3 mAb. The variable region of the anti-CD3 Ig heavy chain was cloned, joined with genes for the heavy chain constant region and expressed in a cell line only secreting autologous mouse chi light chains. Thus we obtained cell lines that produced mouse (m) IgM, mIgG3 and chimaeric mouse/human (h) IgM, hlgG1, hlgG2, hlgG3, hlgG4, hlgE and hlgA2 anti-CD3. The matched set of mouse and mouse/human chimaeric anti-CD3 isotypes switch variants was then used to study activation of T cells in an accessory cell-dependent system. hlgG1, hlgG4, hlgE, mlgG2a and mlgE induced T-cell proliferation in PBMC of all donors tested, whereas PBMC from a subset of donors were unresponsive to stimulation with hlgG2, hlgG3, hlgA2, mlgG1 and mlgG2b anti-CD3 mAb. hlgM, mlgM and mlgA were only able to induce T-cell mitogenesis in combination with PMA. Our panel of anti-CD3 mAb variants may prove a powerful tool to study mouse and human isotype-dependent effector functions and their influence on T-cell activation requirements in detail.

Leukocytes and cytokines in the urine of superficial bladder cancer patients after intravesical immunotherapy with bacillus Calmette-Guerin

The urine of superficial bladder cancer patients treated intravesically with BCG was examined for the presence of leukocytes and cytokines. The number of leukocytes was markedly increased 24h and 48h after five or more BCG instillations. Flow cytofluorometric analysis revealed that, in addition to large numbers of granulocytes, monocytes/macrophages and T-lymphocytes were clearly detectable. The T cells were predominantly CD4+ and probably activated, since they expressed IL2 receptors and HLA-DR. The cytokines IL1, IL2, IL6 and TNF alpha were also increased after BCG instillations. These cytokines and leukocytes may play a role in the antitumor activity of BCG.

Activation of interleukin-2 gene transcription via the T-cell surface molecule CD28 is mediated through an NF-kB-like response element

Production of interleukin-2 (IL-2) by human T-lymphocytes can be augmented by costimulation via CD28. It has been reported that signaling via CD28 acts by stabilization of lymphokine mRNAs (Lindsten, T., June, C. H., Ledbetter, J. A., Stella, G., and Thompson, C. B. (1989) Science 244, 339-343). Here we demonstrate that costimulation via CD28 also provides a signal which activates transcription of the IL-2 gene A CD28-responsive element (CD28RE) in the IL-2 enhancer at position -162 to -152 was identified. This so far unidentified element shows sequence similarity to the kB enhancer motif. In vitro binding studies have demonstrated that the via CD28-induced signal synergizes with either phorbol myristate acetate or anti-CD3 for the induction of a nuclear factor that binds CD28RE and the human immunodeficiency virus (HIV-1) NF-kB motif. The significance of the sequence similarity of CD28RE with the kB enhancer motif was demonstrated by cross-competition studies using unlabeled CD28RE, HIV-1 NF-kB binding site, and a mutated version of the NF-kB motif. In addition, we found that NF-kB-dependent reporter gene expression was induced by costimulation via CD28. These results indicate that besides an effect on lymphokine mRNA stabilization, stimulation via CD28 acts at the level of transcription via coinduction of an NF-kB-like activity.

T cell receptor/CD3 and CD28 use distinct intracellular signaling pathways

Ligation of the T cell membrane antigen CD28 strongly enhances cytokine secretion in human T lymphocytes that are activated via T cell receptor (TcR)/CD3 or CD2 molecules. This study was undertaken to investigate whether, as has been indicated for activation via TcR/CD3, stimulation via CD28 is dependent on the activation of protein kinase C (PKC). Two inhibitors of PKC, 1-alkyl 2-methyl-glycerol and staurosporine, caused a dose-dependent inhibition of T cell proliferation induced by anti-CD3 monoclonal antibodies (mAb). The induction of interleukin (IL) 2 secretion was found to be more sensitive to the effects of the PKC inhibitors than the up-regulation of IL 2 receptor expression. In marked contrast, the anti-CD28 mAb-mediated enhancement of T cell proliferation and IL 2 secretion were insensitive to the action of either compound. We conclude that two independent signaling pathways may be operational in human T cells. The first used by TcR/CD3 depends on the activation of PKC, whereas the second is employed by CD28 and functions independently of PKC.

Interleukin-6 and its relation to the humoral immune response and clinical parameters in burned patients

The cytokine interleukin-6, which has been shown to be increased in patients with burn injuries, is produced by activated monocytes and endothelial cells and has many in vitro activities, including stimulation of acute-phase protein synthesis in hepatocytes, immunoglobulin synthesis in B lymphocytes, and stimulation of growth of megakaryocytes. In 13 patients with a mean of 31% full-thickness burns, we studied the relation of serum interleukin-6 to clinical parameters and parameters of the acute-phase response and immunoglobulin production. Interleukin-6 was already elevated within hours after the injury was sustained, and it remained elevated for several weeks. All components of the acute-phase response were observed: fever, tachycardia, leukocytosis with an associated left shift, elevation of C-reactive protein and alpha 1-antitrypsin, and a decrease in albumin levels. In the second week after burn injury, immunoglobulin M levels peaked, followed by a prolonged elevation of immunoglobulin G levels. Thrombocyte counts initially decreased and rebounded to supranormal levels after 2 weeks. Interleukin-6 levels were positively correlated with acute-phase responses. We believe that the production of interleukin-6 induces the synthesis of acute-phase proteins. High interleukin-6 levels may also be an etiologic factor in the marked immunoglobulin response observed. Likewise, the relation between the megakaryocyte-promoting activity of interleukin-6 and the rebound thrombocytosis requires further investigation.

Tumor necrosis factor (TNF) inhibits interleukin (IL)-1 and/or IL-6 stimulated synthesis of C-reactive protein (CRP) and serum amyloid A (SAA) in primary cultures of human hepatocytes

Interleukin (IL)-1, IL-6 and tumor necrosis factor (TNF) are considered as important mediators for the modulation of liver synthesis of acute phase proteins. However, studies of the direct effect of individual or a combination of these cytokines on the synthesis of acute phase proteins in human hepatocytes are still very limited. In this study, we have examined the synthesis of C-reactive protein (CRP) and serum amyloid A (SAA) in primary cultures of human hepatocytes exposed to recombinant(r)IL-1 alpha (100 U/ml), rIL-6 (2000 U/ml), rTNF alpha (30 U/ml) and to various combinations of these cytokines in the presence of 1 microM dexamethasone. Monoclonal antibodies to rTNF alpha and monospecific anti-rIL-6 sheep antiserum were also used to investigate the possible endogenous production of TNF or IL-6. The findings indicate: (1) IL-1 and IL-6 are stimulatory cytokines for the liver synthesis of CRP and SAA. Anti IL-6 abolishes the stimulatory effect of IL-1. These findings support the previous observation and indicate that IL-1 exerts its action on the enhanced synthesis of CRP and SAA at least in part via IL-6 production in the liver cell. (2) TNF is an inhibitory cytokine for the liver synthesis of CRP. It inhibits also the stimulatory effect of IL-1 and IL-6 on the synthesis of CRP and SAA. (3) Since anti-TNF enhances the stimulatory effect of IL-6 on the synthesis of CRP and SAA, it seems likely that TNF is also produced by the human hepatocytes. However, further studies for more direct evidence of the liver cell production of TNF, such as the detection of TNF messenger RNA are required.

Characterization of an interleukin-6-mediated autocrine growth loop in the human multiple myeloma cell line, U266

It has been reported recently that freshly isolated human myeloma cell cultures proliferate in response to added interleukin-6 (IL-6). Endogenous levels of IL-6 found in the same cultures suggested that an autocrine growth loop may contribute to cell growth. However, the lack of homogenous cell populations in primary myeloma cultures has made it difficult to distinguish between paracrine and autocrine growth mechanisms. To precisely address the autocrine growth issue we have evaluated the growth of the human myeloma cell line, U266. We have found that a neutralizing anti-IL-6 monoclonal antibody can inhibit U266 proliferation. Furthermore, the addition of IL-6 antisense oligonucleotides also inhibits U266 proliferation. These effects are reversed by adding IL-6, suggesting the presence of an autocrine loop. Using bioassays with two different IL-6-dependent cell lines, we were able to detect IL-6 in concentrated U266 supernatants. IL-6 mRNA was detected by polymerase chain reaction amplification of cDNA. Cell cycle parameter analysis shows that IL-6 acts to release a block in G1. Taken together these results present conclusive evidence for IL-6-mediated autocrine growth in the U266 human myeloma cell line.

Human transferrin allows efficient IgE production by anti-CD3-stimulated human lymphocytes at low cell densities

A solid-phase-coupled anti-CD3 T cell activation system was used to study the regulation of human IgE production in vitro. Using 5000 peripheral blood lymphocytes from healthy donors, containing 10%-20% B lymphocytes and no monocytes. IgE was produced very efficiently on a per cell basis. A key observation was that apart from interleukin (IL) 4, human transferrin was essential for IgE production. Furthermore it was found that IgE was produced at low densities only; at higher cell concentrations IgE production was completely abrogated, whereas IgM production increased with increasing cell density. This inhibition at higher cell densities is probably mediated by IL2. Addition of low amounts (6 U/ml) of IL2 strongly enhanced IgE and IgM production at low cell densities, but higher concentrations of IL2 (50 U/ml) were strongly inhibitory for IgE production.

Human osteoblastlike cells do not respond to interleukin-6

Interleukin 6 (IL-6) exerts well-established effects on cells of the immune system as well as on various other cell types. It has been implicated in the control of connective tissue cells in such conditions as rheumatoid arthritis and osteoporosis. We have investigated the effects of recombinant human interleukin-6 (rhIL-6) on human osteoblastlike cells derived from explants of trabecular bone. ROS 17/2.8 cells were used as an additional osteoblastlike cell model system. We were unable to identify any effects of rhIL-6 (5-5000 pg/ml) on the proliferation, alkaline phosphatase activity. osteocalcin production, or release of cytokines or prostaglandins by either osteoblastlike cell model system. Since we have shown previously that these cells release IL-6 in culture, we used a sheep anti-human IL-6 antibody to investigate the possibility that (1) action of added exogenous IL-6 could be masking endogenous production, and (2) endogenous IL-6 may regulate the effects of osteotropic agents on the osteoblastlike cells. Presence of the antibody exerted no detectable effects on 1,25-(OH)2D3-stimulated alkaline phosphatase or on proliferation or TNF production enhanced by IL-1. Thus IL-6 does not appear to be involved in the regulation of osteoblast activity.

Experimental endotoxemia in humans: analysis of cytokine release and coagulation, fibrinolytic, and complement pathways

Endotoxemia was evoked by bolus injection of Escherichia coli endotoxin (2 ng/kg body weight) in six healthy subjects to investigate the early kinetics of cytokine release in relation to the development of clinical and hematologic abnormalities frequently seen in gram-negative septicemia. The plasma concentration of tumor necrosis factor (TNF) increased markedly after 30 to 45 minutes, and reached a maximal level after 60 to 90 minutes. In each volunteer, the initial increase of plasma interleukin 6 (IL-6) concentrations occurred 15 minutes after the initial TNF increase, and maximal IL-6 concentrations were reached at 120 to 150 minutes. A transient increase in body temperature and pulse rate occurred simultaneously with the initial TNF and IL-6 increases, whereas a significant decrease in blood pressure occurred after 120 minutes. These changes were proportional to the changes in TNF and IL-6 concentrations. Coagulation activation, as assessed by a rise of prothrombin fragments and thrombin-antithrombin III complexes, was noted after 120 minutes, in the absence of activation of the contact system. A two- to sixfold increase in the concentrations of tissue plasminogen activator (t-PA) and von Willebrand factor antigen indicated endothelial cell activation. This increase started at 120 and 90 minutes, respectively. The release of t-PA coincided with activation of the fibrinolytic pathway, as measured by plasmin-alpha 2-antiplasmin complexes. The fibrinolytic activity of t-PA was subsequently offset by release of plasminogen activator inhibitor, observed 150 minutes after the endotoxin injection, and reaching a peak at 240 minutes. No complement activation was detected. These results show that in humans endotoxin induces an early, rapidly counteracted fibrinolytic response, and a more long-lasting activation of thrombin by a mechanism other than contact system activation. In addition, our data suggest that endotoxin-induced leukopenia and endothelial cell activation are mediated by TNF.

The relation among stress, adrenalin, interleukin 6 and acute phase proteins in the rat

Stress reactions exist in many conditions in which plasma interleukin 6 (IL-6) is elevated. Examples are burns and sepsis. In these situations fever is often present. These stress situations are always accompanied with high levels of adrenalin and corticosteroids. These hormones, especially when given together, elicit a definite response of acute phase proteins in normal rats. In two stress models, (i) laparotomy and (ii) fever induced by administration of PGE2 in the lateral intracerebral ventricle, we observed a rise of adrenalin and corticosteron followed by an elevated level of plasma IL-6. Therefore, we studied the effect of adrenalin and corticosteron on the plasma level of IL-6. Adrenalin evokes high levels of IL-6, and this effect can be blocked by propranolol. When IL-6 release is blocked in this way, the response of alpha 2 macroglobulin and the cysteine protease inhibitor, both fast-reacting acute phase proteins in rat, is strongly depressed. Isoprenalin, an adreno beta 2 agonist, also causes very high levels of IL-6, indicating that the release of IL-6 can be mediated by an adreno beta 2 receptor whose presence has been demonstrated in monocytic cells. The results suggest a relation between stress situations and IL-6 and may be another factor besides the presence of endotoxins, virus, etc. explaining the high levels of IL-6 observed in many serious clinical situations.

Structure-function analysis of human IL-6. Epitope mapping of neutralizing monoclonal antibodies with amino- and carboxyl-terminal deletion mutants

To study the active site(s) of IL-6 we combined mutagenesis of IL-6 with epitope mapping of IL-6 specific mAb. In addition to amino-terminal deletion mutants we described previously, carboxyl-terminal deletion mutants were prepared. Functional analysis showed that deletion of only five carboxyl-terminal amino acids already reduced the bioactivity 1000-fold. A panel of mAb to IL-6 was subsequently analyzed by antibody competition experiments and binding to the amino- and carboxyl-terminal deletion mutants. On the basis of the competition experiments the six neutralizing mAb were divided in two groups (I and II). The binding pattern with the deletion mutants suggested that the region recognized by the four mAb in group I is composed of residues of amino- and carboxyl-terminus: binding of two mAb was abolished after deletion of amino acid Ala I-Ile26, of the third mAb after deletion of the four carboxyl-terminal amino acids whereas the fourth mAb did not bind to either mutant. Group II mAb retained binding to these mutants. Taken together these data suggest that in the native IL-6 molecule amino acid residues of amino and carboxyl terminus are in close proximity and that together they constitute an active site. Furthermore our data suggest that the part of the molecule recognized by group II antibodies is a second site involved in biologic activity.

Structure-function analysis of human IL-6. Epitope mapping of neutralizing monoclonal antibodies with amino- and carboxyl-terminal deletion mutants

To study the active site(s) of IL-6 we combined mutagenesis of IL-6 with epitope mapping of IL-6 specific mAb. In addition to amino-terminal deletion mutants we described previously, carboxyl-terminal deletion mutants were prepared. Functional analysis showed that deletion of only five carboxyl-terminal amino acids already reduced the bioactivity 1000-fold. A panel of mAb to IL-6 was subsequently analyzed by antibody competition experiments and binding to the amino- and carboxyl-terminal deletion mutants. On the basis of the competition experiments the six neutralizing mAb were divided in two groups (I and II). The binding pattern with the deletion mutants suggested that the region recognized by the four mAb in group I is composed of residues of amino- and carboxyl-terminus: binding of two mAb was abolished after deletion of amino acid Ala I-Ile26, of the third mAb after deletion of the four carboxyl-terminal amino acids whereas the fourth mAb did not bind to either mutant. Group II mAb retained binding to these mutants. Taken together these data suggest that in the native IL-6 molecule amino acid residues of amino and carboxyl terminus are in close proximity and that together they constitute an active site. Furthermore our data suggest that the part of the molecule recognized by group II antibodies is a second site involved in biologic activity.

Interleukin-6 enhances human Ig production, but not as a terminal differentiation factor for B lymphocytes

Most B-cell differentiation systems are complicated by the fact that they are both T-cell- and monocyte-dependent. Immobilized anti-CD3 antibodies induce monocyte-independent T-cell activation, allowing investigation of the role of interleukin-6 (IL6) in the process of B-cell differentiation. We observed that in this system, the addition of monocytes to purified lymphocytes does not influence T-cell proliferation but it does enhance the induction of Ig production. IL6 can specifically replace monocytes in this enhancing effect on both IgM and IgG production. Anti-CD3-induced Ig production appears to be dependent on both IL2 and IL6 since it was inhibited by anti-CD25 (anti-IL2-R) antibodies as well as by anti-IL6 antibodies. Kinetic studies of IL6 addition showed that IL6 is only necessary during the first two days of culture. Our data indicate that IL6 plays an essential role in anti-CD3-induced Ig production, but not as a terminal differentiation factor.

Interleukin-6 and interleukin-1 production in acute leukemia with monocytoid differentiation

Several authors have reported the in vitro production of colony-stimulating factors (CSF) and interleukin-1 (IL-1) by the neoplastic cells from patients with acute myeloid leukemia (AML). Using a sensitive bioassay for IL-6, the capacity of the leukemic cells of 30 patients with AML to produce IL-6 was examined. IL-6 production was found to be specific for cells from patients with an AML with monocytic differentiation (12 of 15 M4 and M5 patients, 0 of 15 M1 and M2 patients). Moreover, IL-6 production was paralleled by IL-1 production. The IL-6- and IL-1-producing cells were mainly found in the more mature monocytic cell fractions, defined as CD14-positive and CD34-negative adherent cells. By limiting dilution experiments, it could be excluded that the production of IL-1 or IL-6 was due to contamination with normal monocytes.

Increased plasma levels of interleukin-6 in sepsis

Interleukin-6 (IL-6) is likely to be an important mediator of the inflammatory response. We measured levels of this cytokine in plasma samples from 37 patients with sepsis or septic shock obtained at the time of admission to the intensive care unit and related these levels to hemodynamic and biochemical parameters as well as to clinical outcome. In 32 of the 37 patients, increased levels of IL-6 were found, occasionally up to 7,500 times the normal level. The highest IL-6 levels were encountered in patients who suffered from septic shock (P value of the difference between patients with and without shock less than .0001). In addition, IL-6 significantly correlated with plasma lactate (P less than .0001), heart rate (P = .05) and, inversely, with mean arterial pressure (P = .01) and platelet counts (P = .0002). Significant correlations of IL-6 with the anaphylatoxins C3a (P = .0001) and C4a (P = .0002) and with the main inhibitor of the classical pathway of complement, C1-inhibitor (inverse correlation, P = .05), were also observed. IL-6 on admission appeared to be of prognostic significance: levels were higher in septic patients who subsequently died than in those who survived (P = .0003), in particular when only patients with septic shock were considered (P less than .0001). All nine septic patients with levels of less than 40 U/mL on admission survived, whereas 89% of the nine patients with levels exceeding 7,500 U/mL died. These data provide evidence for a role of IL-6 in the pathophysiology of septic shock. Further studies are needed to reveal whether IL-6 in sepsis is directly involved in mediating lethal complications or whether it is to be considered as an "alarm hormone" that reflects endothelial cell injury probably mediated by the anaphylatoxines.

Immobilized anti-CD3 monoclonal antibodies induce accessory cell-independent lymphokine production, proliferation and helper activity in human T lymphocytes

Monoclonal antibodies (mAb) directed against the human CD3 molecular complex are able, when immobilized on the plastic of microtitre wells, to induce accessory cell-independent T-cell proliferation. In this study, we show that the anti-CD3 mAb CLB-T3/3 induces strong T-cell stimulation that is proportional to the density of the immobilized antibody. T cells, optimally stimulated with plastic-immobilized CLB-T3/3, showed a five-fold higher proliferation compared to cells that were stimulated with soluble anti-CD3 in the presence of accessory cells. The difference in magnitude of proliferation was found to be correlated with the expression of the CD25 (TAC) antigen and the production of interleukin (IL)-2, but not with the number of high-avidity IL-2 receptors expressed on the surface of these differentially activated cells. In addition, immobilized CLB-T3/3 initiated the production of interferon-gamma (IFN-gamma), but not of IL-4, in purified T lymphocytes. Coated anti-CD3 mAb induced helper activity in T cells for IgM and IgG production by B lymphocytes. Whereas addition of IL-1 or IL-2 had only a moderate effect on T-cell proliferation induced by immobilized anti-CD3 mAb, helper activity was strongly enhanced in the presence of these factors. This T-cell activation system may prove useful for a standardized analysis of both activation requirements and immunoregulatory capacities of human T cells.

Analysis of human IL-6 mutants expressed in Escherichia coli. Biologic activities are not affected by deletion of amino acids 1-28

We have constructed and analyzed amino terminally deleted analogs of IL-6. Progressively shortened variants of mature IL-6 were constructed at the cDNA level and expressed in Escherichia coli. Mutant proteins were recovered from refractile bodies by solubilizing in 6 M guanidine-HCl. The mutant protein concentration in these preparations was estimated by Western blotting by using an IL-6-specific mAb and the biologic activity was measured in the B9 (hybridoma growth factor) assay. The first 28 amino acids of mature IL-6 could be removed without significantly affecting biologic activity. A further removal of amino acids 29 and 30 resulted in an approximately 50-fold decrease, whereas removal of amino acids 31 to 34 virtually abolished the activity. The mutants showed the same reaction pattern in three other IL-6 assays: induction of murine thymocyte proliferation, induction of fibrinogen synthesis by a human hepatoma cell line (HepG2), and the induction of IgM synthesis by an EBV-transformed B cell line. This suggests that a single functional domain might be responsible for all four activities of IL-6.