IgG1 plasmacytosis in interleukin 6 transgenic mice

Cytokines in rheumatoid arthritis

Joints with rheumatoid arthritis are a site for chronic inflammation involving T cells, B cells, macrophages and dendritic cells. When these cells interact cytokines are likely to be produced. The presence of different cytokines in the synovial fluid of patients with rheumatoid arthritis has been studied and the macrophage derived cytokines such as IL-1, IL-6, TNF-alpha, TGF-beta and PDGF have usually been detected in large quantities, whereas T cell produced cytokines (IL-2, IL-4, IFN-gamma) are absent or present in small quantities. IL-1, IL-6 and TNF-alpha have several functions which suggest that they participate in the chronic disease process of rheumatoid arthritis, such as increasing production of eicosanoid, collagenase and prostaglandin E2. Many synovial B cells are activated and produce large amounts of immunoglobulins. We searched for a B cell stimulatory activity in rheumatoid synovial fluid and found a B cell differentiation and helper activity. Cytokines in the joints of patients with rheumatoid arthritis seem central for the propagation of the disease process. Specific intervention in cytokine production or in its effects might help to relieve symptoms in rheumatoid patients.

v-abl does not abolish IL-6 requirement by murine plasmacytoma cells

Activation of c-myc by juxtaposition to an immunoglobulin locus and introduction of the v-abl oncogene act synergistically in generating a mouse plasmacytoma (PC). The question arose whether the effect of v-abl could be attributed to a deregulation of interleukin-6 (IL-6) production or responsiveness, in view of the fact that IL-6 exerts potent growth-stimulatory activity on PC cells. We studied the effect of IL-6 on the in vitro growth of primary PCs induced by pristane alone (TEPCs) or by pristane + A-MuLV (ABPCs). Five of 13 TEPCs and 3 of 7 ABPCs responded to IL-6. Macrophage supernatants prepared from both TEPCs and ABPCs had similar stimulatory effects on PC cells. From 30 primary PCs (including both TEPCs and ABPCs), we established 9 in vitro lines, 2 of which expressed v-abl. All were able to grow on macrophage feeder layers. Three types of behavior could be distinguished on the basis of growth in feeder-free cultures in the presence and absence of IL-6. Group I contained 4 IL-6-dependent lines. Group II contained 2 IL-6-independent lines (one v-abl expressor) that grew faster in the presence of IL-6. Group III consisted of 3 feeder-dependent lines (one v-abl expressor) that were not significantly stimulated by IL-6. These findings indicate that v-abl expression does not influence IL-6 dependence or responsiveness by itself. The supernatant of one line in group II was able to stimulate PC cells. All 6 lines of Groups I and II carried a typical (12;15) translocation, while all 3 lines in group III had a variant (6;15) or (15;16) translocation.

Interleukin 6 (IL-6) and its receptor: their role in plasma cell neoplasias

Interleukin 6 (IL-6) is a multifunctional cytokine regulating immune response acute phase reaction and hematopoiesis. IL-6 plays a critical role in B cell differentiation to plasma cells and is a potent growth factor for plasmacytoma and myeloma. Abnormal production of IL-6 has been suggested to be involved in polyclonal plasma cell abnormalities and plasma cell neoplasias. The deregulated expression of the IL-6 gene in transgenic mice resulted in the generation of malignant plasmacytoma. Based on these findings, it could be considered that continuous IL-6 gene expression plays an essential role in a multistep oncogenesis of plasma cell neoplasias. The role of IL-6 and its receptor in the generation of plasma cell neoplasias and the mechanisms of the IL-6 gene expression and IL-6 receptor-mediated signal transduction are described.

The role of oil and agalactosyl IgG in the induction of arthritis in rodent models

The proportion of agalactosyl IgG [Gal(O)] is raised in human rheumatoid arthritis and tuberculosis. We report here that injection of pristane into the peritoneal cavities of mice on days 0 and 50, which is known to induce plasmacytomas and arthritis, also induced a rise in the proportion of Gal(O), correlating with a simultaneous rise in the level of IgG antibody binding to the 65-kDa heat-shock protein of Mycobacterium bovis (hsp65). Arthritis developed in a proportion of those CBA/Igb mice with the highest percentage of Gal(O). Pretreatment with 50 micrograms of recombinant mycobacterial hsp65 intraperitoneal (i.p.) on day -10, or with 500 rad irradiation on day -2 before the first of the two injections of pristane reduced the incidence of arthritis from 24% in control animals, to 5.3% and 0.4%, respectively. The reduced incidence of disease correlated with smaller rises in the % Gal(O) at 50-75 days, although levels at 150-200 days were not affected. The arthritogenic effect of oil was not confined to the pristane model, since a single i.p. injection of oil 21 days before immunizing DBA/1 mice with type II collagen reduced the mean day of onset of this arthritis, [which we have previously shown to correlate with raised % Gal(O)], from 38 to 15 days (p less than 0.001). One interpretation is that an autoimmunogenic stimulus, given when % Gal(O) is raised, is more likely to evoke disease. Since oil granulomata are known to secrete interleukin 6, which has B cell-regulatory properties and is secreted by rheumatoid synovial cells, we tested sera from interleukin 6-transgenic mice, and found a strikingly raised percentage of Gal(O). We suggest, therefore, that the role of oil in the induction of arthritis is the dysregulation of cytokine release of which a raised percentage of Gal(O) may be a direct or indirect consequence, associated with an increased susceptibility to autoimmunogenic stimuli.

Interleukin-1 beta and tumor necrosis factor-alpha induce gene expression and production of leukocyte chemotactic factors, colony-stimulating factors, and interleukin-6 in human mesangial cells

The capacity of human cultured mesangial cells to produce soluble factors potentially relevant for mechanisms of inflammation and immunity at the glomerular site was analyzed. The nature of the secreted factors initially was investigated by Northern blot analysis using total cellular RNAs isolated from resting and activated mesangial cells. On exposure of mesangial cells to human recombinant interleukin-1 beta (IL-1 beta), high levels of interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) mRNAs were detected. Similar transcripts were found after stimulation with human recombinant tumor necrosis factor-alpha (TNF-alpha). Active secretion of IL-8 was documented by radioimmunoassay in supernatants of mesangial cells activated by either IL-1 beta or TNF-alpha. Using an in vitro migration assay, supernatants from resting mesangial cells were found to be devoid of any chemotactic activity for granulocytes or monocytes. On stimulation with IL-1 beta, however, mesangial cell supernatants expressed MCP-1 biologic activity detected as induction of a strong migratory response for human monocytes but not for granulocytes. In addition, IL-1 beta and TNF-alpha induced high levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) mRNAs. Similarly IL-1 beta and TNF-alpha induced the interleukin-6 (IL-6) gene and active secretion of its mature protein. These data strongly support an effector role for mesangial cells in modulating immune-inflammatory responses in glomeruli. Release of cytokines may activate not only infiltrating inflammatory cells through short paracrine pathways, but also mesangial cells themselves through an autocrine pathway.

Increased expression of the c-myc gene may be related to the aggressive transformation of human myeloma cells

Alteration and abnormal expression of the c-myc oncogene were investigated in human multiple myeloma. Human myeloma cells were highly purified (more than 95%) from bone marrow aspirates in 14 cases of advanced multiple myelomas and one case of plasma cell leukaemia. Southern blotting revealed that a rearranged configuration of c-myc gene was found in only one case of them, but this was a novel truncation of the gene in its coding exon II; a rearranged 3.4 kb band was detected by digestion with Xba I using c-myc exon II probe, but no rearranged band was found using exon III probe. In this case, the truncated c-myc allele was not transcribed; normal sized (2.4 kb) c-myc mRNA was markedly expressed, but no aberrant mRNA was detected. On the other hand, by Northern blotting, the nine cases, including the case with the rearranged c-myc gene, showed increased expression of normal sized (2.4 kb) c-myc mRNA. Elevated c-myc mRNA expressions were well related to the in vitro proliferation (3H-TdR uptake), but not to IL-6 response. Interestingly, extremely high expressions of c-myc mRNA were detected in two cases of aggressive myelomas, including the case with the rearranged c-myc gene, and in one of plasma cell leukaemia. These two cases of aggressive myelomas were the ones who showed the markedly high 3H-TdR uptakes, and had the common clinical features with the formation of an extramedullary mass and very short survival. These results suggest that the activation of c-myc gene could induce high proliferative activities and the subsequent aggressive transformation of myeloma cells.

In vivo effects of anticytokine antibodies on isotype restriction in Mesocestoides corti-infected BALB/c mice

Chronic infection of mice with the cestode Mesocestoides corti results in an antibody response restricted to immunoglobulins M (IgM) and G1 (IgG1). To determine which of the known lymphokines are involved in the restricted isotype response, we treated M. corti-infected mice with a panel of anticytokine monoclonal antibodies against interleukin-4 (IL-4), IL-5, IL-6, and gamma interferon. The effects of anti-IL-4 were of particular importance, since IL-4 is known to enhance IgG1 production and an IgG1 response predominates in infected animals. Interestingly, injection of anti-IL-4 alone had no effect on IgG1 levels at day 7 postinfection and actually enhanced levels at day 10. Decreases in IgM levels were observed in anti-IL-4-treated mice. Administration of anti-IL-5 inhibited IgM production early in infection, but no effects on IgG1 levels were observed. Treatment of infected mice with anti-gamma interferon had no effect on any of the isotypes analyzed. Treatment of infected mice with anti-IL-6 antibody had the most dramatic effects, with inhibition of IgM and IgG1 by day 14 of infection. The transient expression of IgG3, which is sometimes observed very early in the infection process, was also inhibited by anti-IL-6, suggesting that the inhibition observed was not isotype specific. To determine whether cytokines were acting in concert to effect the high IgM and IgG1 levels in infected animals, anticytokine antibodies were also injected in combinations. However, the only combinations that inhibited IgG1 levels contained anti-IL-6, and the extent of inhibition was not greater than that of anti-IL-6 alone. Results are discussed in terms of the effects of cytokines on parasite-induced isotype expression and the potential for IL-4-independent mechanisms of IgG1 production.

Transforming growth factor-beta and suppression of humoral immune responses in HIV infection

We reported previously that PBMC from HIV+ patients spontaneously release increased levels of TGF beta 1, contributing to defects in cellular immune responses. This study defines the implications of TGF beta overexpression for humoral immunity in HIV infection. We found that upon Staphylococcus aureus Cowan I (SAC) stimulation of cells from HIV+ donors, B-lymphocyte proliferative responses were decreased. This deficiency correlated closely (r = 0.7, P less than 0.001) with increased TGF beta secretion by PBMC from HIV-infected donors. Conditioned medium from HIV+ PBMC and purified TGF beta 1 had similar inhibitory effects on SAC- or EBV-induced B-cell proliferation, and B cells from HIV-infected donors were as sensitive to inhibition by TGF beta as cells from normal donors. Antibodies to TGF beta 1 neutralized the inhibitory effect of HIV+ culture supernatants on normal B cells and increased low proliferative responses by HIV+ cells. Using PWM as stimulus for B cell differentiation, it was shown that activated TGF beta from HIV+ PBMC is able to significantly reduce the induction of immunoglobulins and this effect was also abrogated by anti-TGF beta. These studies support the concept that in HIV infection, TGF beta is a potent suppressor, not only of the cellular, but of the humoral immune responses as well.

Production of an hybridoma library to recombinant porcine alpha I interferon: a very sensitive assay (ISBBA) allows the detection of a large number of clones

The preparation of a panel of hybridoma cell lines secreting monoclonal antibodies (MAbs) specific for Recombinant Porcine Alpha I Interferon is reported. Of these MAbs, 28 were subcloned and 21 secreted their antibody during several months. They were partially characterized for their ability to bind and neutralize Alpha Interferons (IFNs-alpha) from different animal species. All the clones bound Recombinant Porcine IFN-alpha 1, 8 bound Human leukocyte IFN, and one bound recombinant Human IFN-alpha 2b, but not IFN-alpha 2a. Two screening procedures were used for the detection of specific MAbs: neutralization assay and immunosorbent binding bioassay. This last method appears to be simple and very sensitive since it permits to detect 100 pg/ml MAb. In addition it can detect weakly, as well as strongly neutralizing antibodies. Probable mechanisms involved in this assay, and possible applications of this method for IFNs-alpha subtyping are discussed.

Effect of leukocyte stimulation on rabbit immune complex glomerulonephritis

Phytohemagglutinin (PHA), a leukocyte mitogen, induces a lymphocyte and blast cell glomerulonephritis in rat renal allografts (Cell Immunol 13:146, 1974). The aim of this study was to assess whether PHA similarly enhances rabbit monocyte-dependent experimental, acute immune complex glomerulonephritis, and whether this effect is associated with local release of interleukin-1 (IL-1) and tumor necrosis factor (TNF). Rabbits with experimental acute serum sickness (AcSS: Group I) had focal proliferative and exudative glomerulonephritis with immune deposits, scattered subepithelial electron-dense deposits (humps), mild and transient proteinuria, normal creatinine clearance and slightly increased production of IL-1 and TNF from isolated glomeruli. Rabbits with AcSS and injected with PHA (Group II) developed severe lymphocyte and blast cell glomerulonephritis with diffuse endothelial damage; immune deposits were significantly reduced, focal subepithelial electron-dense deposits were absent, proteinuria was increased, creatinine clearance was decreased and production of IL-1 and TNF was markedly augmented as compared to rabbits in Group I. Rabbits with AcSS and injected with IL-1 beta and TNF alpha (Group V) had lesions comparable to those seen in Group II. These results show that PHA, IL-1 and TNF enhance the severity of acute immune complex glomerulonephritis, presumably by activating glomerular endothelial and mesangial cells and resident or infiltrated leukocytes.

Animal models for the biological effects of continuous high cytokine levels

Transgenic animals or animals engrafted with retrovirus-derived expression vectors provide models for studying the in vivo effects of high and continuous serum levels of cytokines. Studies employing these models in order to analyze the biological effects for granulocytes-macrophages colony-stimulating factors (CSFs), granulocytes of interleukin (IL-)2, IL-3, IL-6 and erythropoietin are reviewed. In all of these models, overexpression of the different cytokines achieved by use of these approaches resulted in syndromes that were related to nonneoplastic hyperplasia of the respective target cell population. In some but not all models, these syndromes were lethal, mostly due to hypercellularity. These models allow conclusions about the biological effects of very high and continuous levels of these substances as well as about their regulation in different tissues.

Mouse plasmacytoma growth in vivo: enhancement by interleukin 6 (IL-6) and inhibition by antibodies directed against IL-6 or its receptor

Murine plasmacytomas show a striking dependence on interleukin 6 (IL-6) for their growth in vitro. Here, we present evidence suggesting that IL-6 also plays an essential role in the in vivo development of these tumors. This conclusion is based on the finding that the tumorigenicity of an IL-6-dependent plasmacytoma cell line was increased approximately 100-fold on transfection with an IL-6 expression vector, whereas it was inhibited in animals treated with monoclonal antibodies capable of blocking the binding of IL-6 to its receptor. Injection of these antibodies 1 d before tumor challenge protected greater than 50% of the mice and retarded tumor growth in all animals. Tumors arising in antibody-treated mice retained their IL-6 dependence in vitro, suggesting that the level of protection could be improved if stronger IL-6 antagonists were available.

Dysregulated interleukin 6 expression produces a syndrome resembling Castleman's disease in mice

Interleukin 6 (IL-6) is an important regulator of the acute phase response, T cell function, and terminal B cell differentiation. Excessive or inappropriate production of this cytokine may be involved in a variety of autoimmune and neoplastic disorders. To investigate the consequences of dysregulated synthesis of IL-6 in vivo, a high-titer recombinant retroviral vector produced in psi-2 packaging cells was used to introduce the coding sequences of murine IL-6 into mouse hematopoietic cells. Congenitally anemic W/Wv mice reconstituted with bone marrow cells transduced with the retroviral vector developed a syndrome characterized by anemia, transient granulocytosis, hypoalbuminemia, and polyclonal hypergammaglobulinemia, with marked splenomegaly and peripheral lymphadenopathy. Extensive plasma cell infiltration of lymph nodes, spleen, liver, and lung was noted. The similarity of these findings to those of multicentric Castleman's disease, taken together with the observation that lymph nodes from these patients elaborate large amounts of this cytokine, suggest that the inappropriate synthesis of IL-6 has a primary role in the pathogenesis of this systemic lymphoproliferative disorder.

Interleukin 6 is an autocrine growth factor for mesangial cells

Interleukin 6 (IL-6) induces the acute phase response, differentiation of B cells, proliferation of T cells, thymocytes, hematopoietic progenitors, hybridoma and plasmacytoma cells. Monocytes, T cells, fibroblasts, epithelial and endothelial cells secrete IL-6. Since IL-6 responsive cell-types may participate in the pathogenesis of glomerular inflammation, we studied the secretion of IL-6 by rat MCs, using the IL-6 dependent hybridoma cell line B9. The results of our studies indicate that MCs secrete IL-6 with a molecular weight of 17-42 kDa and isoelectric point of 4.0 to 5.3 MC-IL-6 activity could be blocked by a polyclonal antimurine-IL-6 antibody. MC express IL-6 mRNA as determined by Northern blot. Furthermore, our data demonstrate that IL-6 acts as an autocrine growth factor for MC. Incubation of subconfluent MC with recombinant IL-6 results in a dose-dependent increase of 3H-thymidine incorporation and number of MCs. Moreover, reverse phase HPLC fractions of MC-CM containing IL-6 activity increase 3H-thymidine incorporation by MC. In addition to its possible paracrine role in mediating the immune response in the glomerulus, MC-IL-6 may also be one of the autocrine signals leading to mesangial cell proliferation in vivo.

Expression of an exogenous interleukin 6 gene in human Epstein Barr virus B cells confers growth advantage and in vivo tumorigenicity

The biological role of interleukin 6 (IL-6) molecules in human B cell tumorigenesis was studied by using an episomal expression vector, pHEBoSV-IL6, to introduce stably the human IL-6 gene into human Epstein Barr virus (EBV)-transformed B lymphoblasts. The gene was present in the IL-6-transfected cells in a high copy number and was efficiently expressed, resulting in the secretion of consistent levels of IL-6 molecules. The constitutive expression of the IL-6 gene led to an altered pattern of growth and to a malignant phenotype, as shown by clonogenicity in to an altered pattern of growth and to a malignant phenotype, as shown by clonogenicity in soft agar cultures and tumorigenicity in nude mice. These data suggest that the combined action of EBV, which exerts an immortalizing function, and of the growth-promoting activity of IL-6 molecules, can give rise to fully transformed B cell tumors in immunodeficient subjects.

Constitutive and interleukin-1 (IL-1)-inducible factors interact with the IL-1-responsive element in the IL-6 gene

The interleukin-6 (IL-6) promoter is rapidly and transiently activated with other cytokines, including IL-1, tumor necrosis factor, and platelet-derived growth factor, as well as phorbol esters and agents that increase intracellular cyclic AMP. In this study, we have investigated cis-acting regulatory elements and trans-acting factors responsible for IL-1-induced IL-6 gene expression. Studies on the 5' deletion mutants of the human IL-6 gene suggested that the IL-1-responsive element was mapped within the IL-6 promoter region (-180 to -123) which was homologous to the c-fos serum-responsive enhancer element. Gel retardation assay identified two types of nuclear factors that bound to this region, one constitutive and the other inducible. These two factors recognized a 14-base-pair (bp) palindromic sequence, ACATTGCACAATCT. Furthermore, three copies of this 14-bp palindrome conferred IL-1 responsiveness to the basal enhancerless IL-6 promoter, indicating that a 14-bp-dyad symmetry sequence was an IL-1-responsive element in the IL-6 gene.

Constitutive and interleukin-1 (IL-1)-inducible factors interact with the IL-1-responsive element in the IL-6 gene

The interleukin-6 (IL-6) promoter is rapidly and transiently activated with other cytokines, including IL-1, tumor necrosis factor, and platelet-derived growth factor, as well as phorbol esters and agents that increase intracellular cyclic AMP. In this study, we have investigated cis-acting regulatory elements and trans-acting factors responsible for IL-1-induced IL-6 gene expression. Studies on the 5' deletion mutants of the human IL-6 gene suggested that the IL-1-responsive element was mapped within the IL-6 promoter region (-180 to -123) which was homologous to the c-fos serum-responsive enhancer element. Gel retardation assay identified two types of nuclear factors that bound to this region, one constitutive and the other inducible. These two factors recognized a 14-base-pair (bp) palindromic sequence, ACATTGCACAATCT. Furthermore, three copies of this 14-bp palindrome conferred IL-1 responsiveness to the basal enhancerless IL-6 promoter, indicating that a 14-bp-dyad symmetry sequence was an IL-1-responsive element in the IL-6 gene.

Functional murine interleukin 6 receptor with the intracisternal A particle gene product at its cytoplasmic domain. Its possible role in plasmacytomagenesis

Two species of the cDNAs encoding murine IL-6-R (one is abnormal and the other authentic) have been cloned from a plasmacytoma cell line, P3U1, and BALB/c mouse spleen cDNA libraries. In the cDNA encoding the abnormal IL-6-R, the region corresponding to an intracytoplasmic domain was replaced with a part of the long terminal repeat of the intracisternal A particle gene (IAP-LTR). The authentic IL-6-R consists of 460 amino acids with the domain of the Ig superfamily. The overall homology between murine and human IL-6-R was 69 and 54% at DNA and protein levels, respectively. The extracellular domain after the Ig-like domain of murine IL-6-R was found to have an homology with those of murine erythropoietin R, human IL-2-R beta chain, murine IL-4-R, and human granulocyte-macrophage CSF-R, as in the case of human IL-6-R, and these receptors have been classified as members of the IL receptor family. In P3U1 cells, the expression of the mRNA encoding abnormal IL-6-R was much higher than that of the mRNA encoding authentic IL-6-R. An IL-6-dependent human T cell line, KT-3, which did not respond to murine IL-6, acquired the responsiveness to murine IL-6 when transfected with the cDNA encoding abnormal IL-6-R, indicating that abnormal IL-6-R lacking a normal cytoplasmic domain can function. Since IL-6 functions as a potent growth factor for murine plasmacytomas, over-expression of abnormal IL-6-R may function as a positive selection element for the development of certain plasmacytomas.

Activation of interleukin-6 gene expression through the NF-kappa B transcription factor

The promoter region of the interleukin-6 (IL-6) gene has a putative NF-kappa B-binding site. We found that a fragment of the IL-6 promoter containing the site specifically binds highly purified NF-kappa B protein and the NF-kappa B protein in nuclear extracts of phorbol ester-induced Jurkat cells. Mutations of the NF-kappa B site abolished complex formation with both purified NF-kappa B and the nuclear extract protein. Transient expression of chloramphenicol acetyltransferase (CAT) plasmids containing the IL-6 promoter revealed very little activity of the promoter in U-937 monocytic cells and in HeLa cells before stimulation. However, stimulation of U-937 and HeLa cells by inducers of NF-kappa B led to a dramatic increase in CAT activity. Mutations in the NF-kappa B-binding site abolished inducibility of IL-6 promoter-cat constructs in U-937 cells by lipopolysaccharide, tumor necrosis factor alpha, the double-stranded RNA poly(IC), or phytohemagglutinin and in HeLa cells by tumor necrosis factor alpha and drastically reduced but did not completely eliminate inducibility in HeLa cells stimulated by double-stranded RNA poly(IC) or phorbol 12-myristate 13-acetate. These results suggest that NF-kappa B is an important mediator for activation of the IL-6 gene by a variety of IL-6 inducers in both U-937 and HeLa cells and that alternative inducible enhancer elements contribute in a cell-specific manner to IL-6 gene induction. Because NF-kappa B is involved in the control of a variety of genes activated upon inflammation, NF-kappa B may play a central role in the inflammatory response to infection and tissue injury.

Activation of interleukin-6 gene expression through the NF-kappa B transcription factor

The promoter region of the interleukin-6 (IL-6) gene has a putative NF-kappa B-binding site. We found that a fragment of the IL-6 promoter containing the site specifically binds highly purified NF-kappa B protein and the NF-kappa B protein in nuclear extracts of phorbol ester-induced Jurkat cells. Mutations of the NF-kappa B site abolished complex formation with both purified NF-kappa B and the nuclear extract protein. Transient expression of chloramphenicol acetyltransferase (CAT) plasmids containing the IL-6 promoter revealed very little activity of the promoter in U-937 monocytic cells and in HeLa cells before stimulation. However, stimulation of U-937 and HeLa cells by inducers of NF-kappa B led to a dramatic increase in CAT activity. Mutations in the NF-kappa B-binding site abolished inducibility of IL-6 promoter-cat constructs in U-937 cells by lipopolysaccharide, tumor necrosis factor alpha, the double-stranded RNA poly(IC), or phytohemagglutinin and in HeLa cells by tumor necrosis factor alpha and drastically reduced but did not completely eliminate inducibility in HeLa cells stimulated by double-stranded RNA poly(IC) or phorbol 12-myristate 13-acetate. These results suggest that NF-kappa B is an important mediator for activation of the IL-6 gene by a variety of IL-6 inducers in both U-937 and HeLa cells and that alternative inducible enhancer elements contribute in a cell-specific manner to IL-6 gene induction. Because NF-kappa B is involved in the control of a variety of genes activated upon inflammation, NF-kappa B may play a central role in the inflammatory response to infection and tissue injury.

Interleukin 6 and its receptor in the immune response and hematopoiesis

Interleukin 6 (IL-6) plays critical roles in the immune response and hematopoiesis. It is a potent B cell differentiation factor inducing antibody-forming plasma cells. It enhances interleukin 3-induced proliferation of hematopoietic stem cells. Furthermore, IL-6 induces maturation of megakaryocytes. In IL-6 transgenic mice, a massive polyclonal plasmacytosis and an increase in the number of mature megakaryocytes in the bone marrow were observed. The data indicated that deregulated expression of the IL-6 gene induced a polyclonal plasmacytosis and could be involved in the oncogenesis of plasma cell neoplasias. IL-6 receptor (IL-6R) was molecularly cloned and found to be an immunoglobulin superfamily having an MW of 80 kDa. Upon the binding of IL-6 to its 80 kDa IL-6R, a second non-binding molecule, gp130 was shown to associate with IL-6R. The complex of IL-6 and soluble IL-6R lacking both transmembrane and cytoplasmic domains could bind gp130 and transduce the signal. The results indicate that the IL-6R system consists of two polypeptide chains: one is an 80 kDa ligand-binding molecule and the other is a possible signal transducer, gp130.