Activation of interleukin-1 receptor-associated kinase by gram-negative flagellin

Flagellin from various species of gram-negative bacteria activates monocytes to produce proinflammatory cytokines. We have analyzed the pathway by which Salmonella enteritidis flagellin (FliC) activates murine and human monocyte/macrophage-like cell lines. Since lipopolysaccharide (LPS), the principal immune stimulatory component of gram-negative bacteria, is known to signal through Toll-like receptor 4 (TLR4), we tested the possibility that FliC also signals via TLR4. When murine HeNC2 cells were stimulated with LPS in the presence of a neutralizing anti-TLR4 monoclonal antibody, tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO) production were markedly reduced. In contrast, FliC-mediated TNF-alpha and NO production were minimally affected by the anti-TLR4 antibody. Furthermore, FliC, unlike LPS, stimulated TNF-alpha production in the TLR4 mutant cell line, GG2EE, indicating that TLR4 is not essential for FliC-mediated signaling. To test the possibility that FliC signals via another TLR, we measured FliC-mediated activation of interleukin-1 (IL-1) receptor-associated kinase (IRAK), a central component in IL-1R/TLR signaling. FliC induced IRAK activation in HeNC2 and GG2EE cells as well as in the human promonocytic cell line THP-1. IRAK activation was rapid in HeNC2 cells, with maximal activity observed after 5 min of treatment with FliC. In addition, FliC-mediated IRAK activation exhibited the same concentration dependence as was demonstrated for the induction of TNF-alpha. These results represent the first demonstration of IRAK activation by a purified bacterial protein and strongly suggest that a TLR distinct from TLR4 is involved in the macrophage inflammatory response to FliC.

High-affinity interaction between gram-negative flagellin and a cell surface polypeptide results in human monocyte activation

Flagella from diverse gram-negative bacteria induce tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) synthesis by human monocytes (F. Ciacci-Woolwine, P. F. McDermott, and S. B. Mizel, Infect. Immun. 67:5176-5185, 1999). In this study, we establish that purified flagellin (FliC or FljB), the major filament protein from Salmonella enterica serovar Enteritidis, S. enterica serovar Typhimurium, and Pseudomonas aeruginosa, is an extremely potent inducer of TNF-alpha production by human monocytes and THP-1 myelomonocytic cells. Fifty percent of maximal TNF-alpha production (EC(50)) was obtained with 1.5 x 10(-11) M flagellin (0.75 ng/ml). Mutagenesis studies revealed that the central hypervariable region of flagellin is essential for the TNF-alpha-inducing activity of the protein. Although less active than the wild-type protein, a Salmonella flagellin mutant composed of only the central hypervariable region retained substantial TNF-alpha-inducing activity at nanomolar concentrations. In contrast, the conserved amino- and carboxy-terminal regions are inactive. Mutational analysis of the hypervariable region revealed that it contains two equally active TNF-alpha-inducing domains. The ability of THP-1 cells to respond to purified flagellins is dramatically reduced by mild trypsin treatment of the cells. Taken together, our results demonstrate that the cytokine-inducing activity of flagellins from gram-negative bacteria results from the interaction of these proteins with high-affinity cell surface polypeptide receptors on monocytes.

Proteasome-mediated regulation of interleukin-1beta turnover and export in human monocytes

Interleukin-1beta is a secreted protein that accumulates in the cytosol as an inactive precursor (pIL-1beta) before processing and release of biologically active protein. To understand the impact of this property on IL-1beta production, we examined the intracellular stability of pIL-1beta in lipopolysaccharide (LPS)-stimulated human monocytes. Precursor IL-1beta was degraded with a relatively short half-life of 2.5 h in the promonocytic cell line, THP-1, and in primary monocytes. MG132 (carbobenzoxyl-leucinyl-leucinyl-leucinal) stabilized pIL-1beta levels in THP-1 cells, suggesting that degradation was proteasome-mediated, but this inhibitor was toxic for primary monocytes, causing release of pIL-1beta as well as the cytoplasmic enzyme, lactate dehydrogenase (LDH) into supernatants. In contrast, clasto-lactacystin beta-lactone, a specific inhibitor of the proteasome, caused a dose-dependent stabilization of intracellular pIL-1beta, and this led to a corresponding increase in mIL-1beta and pIL-1beta but not LDH release into culture supernatants. Therefore, by regulating intracellular levels of precursor IL-1beta, the proteasome plays an important and previously unrecognized role in controlling the amount of biologically active IL-1beta that is exported by activated monocytes.

mRNA and protein stability regulate the differential expression of pro- and anti-inflammatory genes in endotoxin-tolerant THP-1 cells

The products of proinflammatory genes such as interleukin-1beta (IL-1beta) and cyclooxygenase-2 (COX-2) initiate many of the events associated with sepsis. Transcription of these genes is subsequently down-regulated, whereas expression of anti-inflammatory genes such as secretory interleukin-1 receptor antagonist (sIL-1 RA) is maintained. Differential expression is associated with endotoxin tolerance, a cellular phenomenon common to sepsis and characterized by reduced proinflammatory gene expression after repeated exposure to lipopolysaccharide. As a model for endotoxin tolerance, we examined the expression of COX-2 and sIL-1 RA in a human promonocyte cell line, THP-1. We observed a 5-fold decrease in COX-2 protein in endotoxin-tolerant cells relative to control cells. In contrast, sIL-1 RA protein increased 5-fold in control and tolerant cells and remained elevated. Decreased COX-2 production is due to repressed transcription and not enhanced mRNA degradation. In addition, COX-2 protein is turned over rapidly. Transcription of sIL-1 RA is also repressed during tolerance. However, sIL-1 RA mRNA is degraded more slowly than COX-2 mRNA, allowing continued synthesis of sIL-1 RA protein that is very stable. These results indicate that differential expression during endotoxin tolerance occurs by transcriptional repression of COX-2 and by protein and mRNA stabilization of sIL-1 RA.

Induction of cytokine synthesis by flagella from gram-negative bacteria may be dependent on the activation or differentiation state of human monocytes

We have previously demonstrated that salmonellae, but not Escherichia coli or Yersinia enterocolitica, stimulates tumor necrosis factor alpha (TNFalpha) production in the human promonocytic cell line U38. Subsequent analysis revealed that the TNFalpha-inducing activity of salmonellae was associated with flagellin, a major component of flagella from gram-negative bacteria. In the present study, we have explored the basis for the apparent specificity of action of Salmonella flagella on TNFalpha expression in U38 cells and have extended this analysis to normal human peripheral blood mononuclear cells (PBMC). Flagella from the enteropathogenic E. coli strain E2348/69, Y. enterocolitica JB580, and Pseudomonas aeruginosa PAO1, which did not induce significant levels of TNFalpha production in U38 cells, were as potent as Salmonella flagella in terms of TNFalpha and interleukin 1beta activation in PBMC. However, TNFalpha production in U38 cells was greatly enhanced when these cells were stimulated with flagella from E. coli, Y. enterocolitica, and P. aeruginosa in the presence of a costimulant, phorbol 13-myristate acetate. These findings are consistent with the hypothesis that the activation or differentiation state of a monocyte may have a substantial effect on the cell's responsiveness to flagellum stimulation of cytokine synthesis. Furthermore, these results indicate that cytokine induction in monocytes may be a general property of flagella from gram-negative bacteria.

Salmonella flagellin induces tumor necrosis factor alpha in a human promonocytic cell line

During infection of the gastrointestinal tract, salmonellae induce cytokine production and inflammatory responses which are believed to mediate tissue damage in the host. In a previous study, we reported that salmonellae possess the ability to stimulate tumor necrosis factor alpha (TNF-alpha) accumulation in primary human monocytes, as well as in the human promonocytic cell line U38. In this model system, cytokine upregulation is not due to lipopolysaccharide but is mediated by a released protein. In the present study, TnphoA transposon mutagenesis was used to identify the TNF-alpha-inducing factor. A mutant Salmonella strain which lacks the ability to induce TNF-alpha was isolated from a TnphoA library. Genetic analysis of this mutant demonstrated that the hns gene has been interrupted by transposon insertion. The hns gene product is a DNA-binding protein that regulates the expression of a variety of unrelated genes in salmonellae. One of the known targets of histone-like protein H1 is flhDC, the master operon which is absolutely required for flagellar expression. Analysis of other nonflagellated mutant Salmonella strains revealed a correlation between the ability to induce TNF-alpha and the expression of the phase 1 filament subunit protein FliC. Complementation experiments demonstrated that FliC is sufficient to restore the ability of nonflagellated mutant Salmonella strains to upregulate TNF-alpha, whereas the phase 2 protein FljB appears to complement to a lesser extent. In addition, Salmonella FliC can confer the TNF-alpha-inducing phenotype on Escherichia coli, which otherwise lacks the activity. Furthermore, assembly of FliC into complete flagellar structures may not be required for induction of TNF-alpha.

Salmonellae activate tumor necrosis factor alpha production in a human promonocytic cell line via a released polypeptide

Invasive strains of Salmonella spp. cause both systemic and localized infections in humans. The ability to resist infection and some aspects of the tissue pathology associated with the presence of Salmonella in the gastrointestinal tract have been shown to be mediated in part by the induction of tumor necrosis factor alpha (TNF-alpha), a proinflammatory cytokine produced by activated macrophages and lymphocytes. Recent reports indicate that TNF-alpha is involved in the induction of human immunodeficiency virus replication by Salmonella in the latently infected human promonocytic cell line U1. In the present study, we investigated the effects of Salmonella on TNF-alpha production in U1 cells and a related cell line, U38. Unlike Escherichia coli or Yersinia enterocolitica, salmonellae rapidly induce TNF-alpha expression in these cells through a released factor(s). Time course experiments show that the kinetics of TNF-alpha production by U38 cells stimulated with Salmonella conditioned medium closely resemble those observed in response to live Salmonella. The observation that TNF-alpha levels are elevated by 60 min after exposure to either bacteria or their conditioned medium suggests that the soluble inducer is continuously released or shed by the bacteria and that the signal acts rapidly to increase TNF-alpha production. Furthermore, the ability to produce the TNF-alpha inducer is shared by at least four Salmonella serotypes and does not correlate with the abilities to invade and to survive within phagocytes. Treatment of active conditioned medium with trypsin, but not low pH, high temperature, or urea, significantly inhibits its TNF-alpha-inducing effect on U38 cells, a finding which points to a polypeptide product of Salmonella as the mediator of TNF-alpha production. Gel filtration chromatography of Salmonella conditioned medium reveals two peaks of activity, consistent with molecular masses of approximately 150 and 110 kDa.

Differential sensitivity of interleukin-1 alpha and -beta precursor proteins to cleavage by calpain, a calcium-dependent protease

In view of the observations that the calcium ionophores, A23187 and ionomycin, enhance the processing and secretion of interleukin-1 (IL-1 alpha) and IL-1 beta from macrophages, and IL-1 alpha processing is mediated by calpain, a calcium-dependent protease, we evaluated the possibility that calpain might also play a role in the processing of IL-1 beta. Whereas calpain-containing P388D1 macrophage lysates and purified calpain processed precursor IL-1 alpha to its mature 17-kDa form, precursor IL-1 beta was degraded by both sources of calpain. However, the activation of calpain in P388D1 cells that were transiently transfected with a cDNA expression vector encoding the precursor form of IL-1 beta did not result in the degradation of precursor IL-1 beta, but did result in the processing and secretion of IL-1 alpha, implying that precursor IL-1 beta is protected from calpain degradation in vivo. Furthermore, calpain did not enhance the processing of the IL-1 beta precursor by the IL-1 beta-converting enzyme. These results indicate that calpain is not involved in the processing of precursor IL-1 beta in vitro or in vivo. The IL-1 beta precursor may be protected from calpain degradation by a sequestering mechanism that involves a cytoplasmic factor(s) that reduces the sensitivity of IL-1 beta to attack by calpain or localizes IL-1 beta to a site that precludes any interaction with the protease. Although MDL 28,170, a calpain inhibitor, prevented the ionomycin-induced processing of precursor IL-1 alpha to the mature protein in P388D1 cells, it did not inhibit the ionomycin-induced secretion of the mature IL-1 alpha and -beta proteins expressed in these cells. These results indicate that a calcium-dependent factor other than calpain is involved in the secretion of the mature IL-1 proteins.

Interleukin 1 activation of the AP-1 transcription complex in murine T cells is regulated at the level of Jun B protein accumulation

We have examined the regulation of the AP-1 DNA transcription complex during T cell activation in response to interleukin 1 (IL-1) and phorbol ester (TPA) treatment of the IL-1 responsive murine thymoma T cell line, EL4 6.1 C 10. IL-1 synergistically enhances the stimulatory effect of TPA on AP-1-mediated gene expression in this cell line. To elucidate the mechanism(s) by which IL-1 enhances AP-1-mediated gene expression, we examined the effect of IL-1 on the synthesis and turnover of Jun B, the member of the jun gene family that is present in AP-1 complexes in EL4 cells. We found that IL-1 + TPA-treated cells contain significantly higher Jun B protein levels than cells treated with TPA alone. IL-1 promotes the prolonged accumulation of Jun B, whereas the cellular content of Jun B decreases dramatically after 6 hr in cells treated with only TPA. IL-1 enhancement of Jun B protein levels is not the result of a change in the turnover rate of the Jun B protein, but rather results from the maintenance of sufficient jun B mRNA to support continued accumulation of newly synthesized protein. In addition to Jun B, we found that the T cell AP-1 complex contains the Fra-1 protein, a member of the fos gene family. Although IL-1 dramatically increases Jun B accumulation, it does not enhance TPA-induced Fra-1 protein levels in EL4 cells. Thus, the stimulation of AP-1-mediated gene expression by IL-1 in EL4 cells is due to the promotion of Jun B protein accumulation that, in turn, facilitates Jun B heterodimerization with TPA-induced Fra-1 protein, thereby forming an active AP-1 complex.

Interleukin-1 beta secretion. A possible multistep process that is regulated in a cell type-specific manner

In a prior study, we found that the processed form of human interleukin-1 beta (mature IL-1 beta) is secreted to a significantly greater extent than the precursor form of the protein, indicating that the precursor domain acts in some manner to reduce the secretory potential of the protein. In view of this observation, we sought to define the sequence(s) in the IL-1 beta precursor that limit the secretion of the protein as well as the sequences in the mature protein that promote secretion. The P388D1 murine macrophage cell line and the Jurkat human T-cell line were transiently transfected with cDNA expression vectors encoding truncated forms of human precursor IL-1 beta proteins, lacking either the first 76, 94, 99, or 104 amino acids. The removal of increasing numbers of precursor amino acid residues resulted in a graded increase in the secretion of the truncated precursor IL-1 beta proteins from both cell lines. The minimal region of the precursor sequence required to inhibit the optimal secretion of IL-1 beta occurs between amino acids 100 and 104 for P388D1 cells and 95-99 for Jurkat cells. Deletion of the amino acids within these regions increased the secretion level of the truncated proteins to that of mature IL-1 beta. Mutagenesis of the mature IL-1 beta sequence revealed that a region of basic amino acids may play an important role in the optimal secretion of mature IL-1 beta in P388D1 cells, but not in Jurkat cells. Based on the differences in the structural requirements for IL-1 beta secretion in P388D1 and Jurkat cell lines, it is likely that the secretion of IL-1 beta may be subject to multiple levels of regulation that are differentially operative in different cell types.

Regulation of macrophage activation and human immunodeficiency virus production by invasive Salmonella strains

Salmonellae possess the ability to adhere to and invade macrophages and in so doing trigger a number of intracellular events that are associated with cellular activation. As an initial approach to defining the mechanisms by which invasive salmonellae alter macrophage function, we have explored the impact of Salmonella infection on the production of human immunodeficiency virus (HIV) in U1 cells, a promonocytic cell line latently infected with the virus. Infection of U1 cells with a pathogenic strain of Salmonella enteritidis resulted in a marked induction of macrophage activation and HIV production. The stimulatory effect of salmonellae was mediated by signals other than lipopolysaccharide. Salmonella mutants with specific defects in invasion or intracellular survival were markedly less effective in the induction of HIV production. In contrast to S. enteritidis, strains of Yersinia enterocolitica, Legionella pneumophila, and Escherichia coli did not induce HIV production. However, all of these bacteria induced comparable levels of gene expression mediated by the HIV long terminal repeat. The results of this study are consistent with the notion that invasive salmonellae possess the ability to activate the macrophage by at least one mechanism that is not shared with several other species of gram-negative bacteria. Furthermore, the expression of this unique property is maximal with Salmonella strains that are not only invasive but also capable of prolonged survival within the macrophage. Our results indicate that the U1 cell line may be a very useful model system with which to examine the biochemical pathways by which internalized salmonellae modulate the activation state of the macrophage.

Characterization of the structural requirements and cell type specificity of IL-1 alpha and IL-1 beta secretion

The murine macrophage cell line, P388D1, was transfected with expression plasmids containing a cDNA for the precursor or mature form of human interleukin (IL)-1 alpha or -1 beta, and the extent of IL-1 protein secretion was analyzed. The secretion of IL-1 beta from cells transfected with a cDNA encoding the mature IL-1 beta was approximately 15-fold greater than from cells transfected with a precursor IL-1 beta cDNA. Although P388D1 cells transfected with precursor and mature IL-1 alpha cDNAs exhibited similar levels of secretion, the precursor IL-1 alpha cDNA-transfected cells secreted only the mature form of IL-1 alpha. Relatively high levels of IL-1 secretion were also observed in cultures of HeLa cells and the murine EL 4 and human Jurkat T cell lines that were transfected with a mature IL-1 alpha or -beta expression plasmid. Secretion was not observed when these cell lines were transfected with precursor IL-1 alpha or -beta expression plasmids. Secretion was also minimal when P388D1 cells were transfected with cDNAs encoding mature IL-1 beta proteins lacking the NH2- or COOH-terminal 20 amino acids. These results indicate that the mature forms of IL-1 proteins are the preferred substrates for secretion and that the maintenance of a specific conformation of these proteins may be required for optimal secretion.

Induction of AP-1 transcription factor components during T-cell activation by interleukin 1 and phorbol esters

We have examined the effect of interleukin 1 (IL-1) and phorbol esters [12-O-tetradecanoylphorbol-13-acetate (TPA)] on the expression of various components of the AP-1 transcription factor complex during T-cell activation. We previously found that a chloramphenicol acetyltransferase reporter gene driven by the collagenase TPA responsive element was expressed upon stimulation of T-cells by TPA and that this expression was enhanced when IL-1 was added as a costimulant; IL-1 alone had no effect on TPA responsive element-chloramphenicol acetyltransferase expression. In this study, we have found that stimulation of T-cells by IL-1 and TPA is accompanied by activation of a subset of immediate early genes that comprise the AP-1 transcription factor complex. junB and fosB were rapidly induced following stimulation with TPA. Although the levels of other fos-related mRNAs were also elevated, their maximal induction was delayed by approximately 5 h. IL-1 alone had little or no effect, but enhanced TPA induced transcription and steady-state levels of these mRNAs. The expression of fos and jun during T-cell activation was accompanied by increased specific binding of JunB, FosB, and fos-related antigen containing complexes to the TPA responsive element. These findings indicate that the synergistic effect of IL-1 and TPA on AP-1 mediated gene expression is due, in part, to the ability of IL-1 to enhance the expression of genes encoding specific AP-1 transcription factor components.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of AP-1 by IL-1 and phorbol esters in T cells. Role of protein kinase A and protein phosphatases

We have examined the regulation of the AP-1 transcription complex in the IL-1-responsive murine T cell thymoma cell line EL-4 6.1 C10. Our results demonstrate that AP-1-mediated gene expression in T cells may be regulated by several signaling pathways and factors, including IL-1, protein kinase C, protein kinase A (PKA), and one or more serine/threonine-specific protein phosphatases. The activation of protein kinase C results in an increase in nuclear AP-1 DNA binding activity, as well as enhanced gene expression. IL-1 and agents that elevate intracellular cAMP levels do not, by themselves, induce AP-1 activation, but they synergize with phorbol esters. IL-1 and forskolin may enhance AP-1 function by different mechanisms, because forskolin enhanced gene expression without producing an increase in nuclear AP-1 DNA binding, whereas IL-1 increased AP-1-binding activity and gene expression. These observations, in conjunction with the lack of a demonstrable effect of IL-1 on cAMP production in EL-4 cells, are consistent with the view that IL-1 enhances AP-1 activation by a pathway that does not directly involve cAMP and PKA. However, the induction of AP-1 activity by IL-1 and phorbol esters is dependent upon the presence of PKA, as evidenced by the loss of AP-1 inducibility in cells transfected with a cDNA encoding protein kinase inhibitor, a specific inhibitor of PKA. The effect of protein kinase inhibitor on AP-1 activation in response to IL-1 and tetradecanoyl-phorbol-13-acetate was reversed in the presence of the serine/threonine protein phosphatase inhibitor okadaic acid. Thus, the level of AP-1 activity in T cells may be determined by the balance between the activities of several serine/threonine protein kinases and phosphatases.

Activation of AP-1 by IL-1 and phorbol esters in T cells. Role of protein kinase A and protein phosphatases

We have examined the regulation of the AP-1 transcription complex in the IL-1-responsive murine T cell thymoma cell line EL-4 6.1 C10. Our results demonstrate that AP-1-mediated gene expression in T cells may be regulated by several signaling pathways and factors, including IL-1, protein kinase C, protein kinase A (PKA), and one or more serine/threonine-specific protein phosphatases. The activation of protein kinase C results in an increase in nuclear AP-1 DNA binding activity, as well as enhanced gene expression. IL-1 and agents that elevate intracellular cAMP levels do not, by themselves, induce AP-1 activation, but they synergize with phorbol esters. IL-1 and forskolin may enhance AP-1 function by different mechanisms, because forskolin enhanced gene expression without producing an increase in nuclear AP-1 DNA binding, whereas IL-1 increased AP-1-binding activity and gene expression. These observations, in conjunction with the lack of a demonstrable effect of IL-1 on cAMP production in EL-4 cells, are consistent with the view that IL-1 enhances AP-1 activation by a pathway that does not directly involve cAMP and PKA. However, the induction of AP-1 activity by IL-1 and phorbol esters is dependent upon the presence of PKA, as evidenced by the loss of AP-1 inducibility in cells transfected with a cDNA encoding protein kinase inhibitor, a specific inhibitor of PKA. The effect of protein kinase inhibitor on AP-1 activation in response to IL-1 and tetradecanoyl-phorbol-13-acetate was reversed in the presence of the serine/threonine protein phosphatase inhibitor okadaic acid. Thus, the level of AP-1 activity in T cells may be determined by the balance between the activities of several serine/threonine protein kinases and phosphatases.

Involvement of a calpain-like protease in the processing of the murine interleukin 1 alpha precursor

Interleukin (IL) 1 alpha is synthesized as a 33-kDa precursor that is enzymatically cleaved to the 15-17-kDa forms that are found in the culture supernatants of activated macrophages. We have explored the possibility that calcium might enhance IL-1 processing and secretion via the stimulation of a calcium-dependent protease. We have found that lysates prepared from human peripheral blood monocytes, the human histiocytic lymphoma cell line U937, and the murine macrophage cell line P388D1 contain a calcium-dependent IL-1 alpha processing activity that cleaves the IL-1 alpha precursor to its mature form. Although NIH 3T3 mouse fibroblast cell lysates also contain IL-1 processing activity, lysates from the murine thymoma EL-4, the human epidermoid cell line HEp-2, and the human foreskin fibroblast line FS-4 lack this activity. IL-1 processing activity is inhibited by leupeptin and exhibits a molecular mass of 80-110 kDa. The processing activity is also inhibited by a monoclonal antibody directed against calpain type I. These results indicate that the processing of the IL-1 alpha precursor is mediated, at least in part, by a member of the calpain family of proteases. Mixing experiments revealed that lysates from EL-4 or HEp-2 cells contain an inhibitor(s) of the calpain-like protease in macrophage extracts. It is, therefore, likely that many non-macrophage cell types are unable to process the IL-1 alpha precursor because the calpain present in these cells is only weakly active due to the presence of a specific inhibitor(s) such as calpastatin.

Expression of interleukin-1 alpha and beta genes by human blood polymorphonuclear leukocytes

Expression of IL-1 alpha and beta genes was studied in human blood PMN with close monitoring of the effects of contaminating mononuclear leukocytes (MNL). We provide evidence that PMN both transcribe and translate IL-1 alpha and beta genes after stimulation with LPS or IL-1 alpha. A combination of mouse thymocyte comitogen proliferation assay, ELISA, and immunocytochemistry was required to establish that IL-1 alpha and beta synthesis observed in preparations of PMN could not be accounted for by the low level of contaminating MNL. Synthesis of IL-1 beta in PMN exceeded that of IL-1 alpha, but little or no IL-1 alpha was released by PMN. Although increases in IL-1 mRNA after stimulation of PMN and MNL with LPS were similar, PMN were less efficient than MNL in translating IL-1 mRNA. In contrast, PMN and MNL IL-1 alpha and beta mRNAs were translated with equal efficiency in rabbit reticulocyte lysates, suggesting that synthesis of IL-1 in PMN is subject to some form of translational control. We conclude that PMN stimulated with LPS efficiently transcribe but inefficiently translate IL-1 genes relative to MNL. IL-1 beta transcription and translation predominates over that of IL-1 alpha, and IL-1 beta is the predominant IL-1 protein released by PMN. IL-1 can induce its own synthesis in PMN.

Involvement of cyclic AMP-dependent protein kinases in the signal transduction pathway for interleukin-1

Expression of a highly specific protein inhibitor for cyclic AMP-dependent protein kinases in interleukin-1 (IL-1)-responsive cells blocked IL-1-induced gene transcription that was driven by the kappa immunoglobulin enhancer or the human immunodeficiency virus long terminal repeat. This inhibitor did not affect protein kinase C-mediated gene transcription, suggesting that cyclic AMP-dependent protein kinases are involved in the signal transduction pathway for IL-1 in a number of responsive cell types.

Detection of IL-1 alpha and IL-1 beta in the supernatants of paraformaldehyde-treated human monocytes. Evidence against a membrane form of IL-1

The concept of a membrane form of IL-1 arose from the observation that paraformaldehyde-treated macrophages display IL-1 bioactivity. Thus far, the biochemical characterization of a membrane form of the molecule has not been reported. In a recent publication we demonstrated that murine IL-1 alpha can be detected in the supernatants of paraformaldehyde-treated macrophages. These data indicate that the phenomenon of membrane IL-1 may result from leakage of IL-1 from inadequately fixed cells. In the current report we have extended our studies toward the examination of human IL-1 alpha and IL-1 beta. IL-1 activity can be detected in the supernatants of paraformaldehyde-treated human monocytes. Although anti-IL-1 alpha, but not anti-IL-1 beta, antibodies can efficiently block the IL-1 bioactivity, both IL-1 alpha and IL-1 beta can be found by immunoprecipitation in the supernatants of the fixed monocytes. IL-1 alpha is efficiently processed to the low m.w. form, whereas IL-1 beta remains predominantly as the inactive, precursor molecule. IL-1 is not found in the supernatants of monocyte membrane preparations, demonstrating that the leakage of IL-1 is from an intracellular, rather than membrane-bound source.

Detection of IL-1 alpha and IL-1 beta in the supernatants of paraformaldehyde-treated human monocytes. Evidence against a membrane form of IL-1

The concept of a membrane form of IL-1 arose from the observation that paraformaldehyde-treated macrophages display IL-1 bioactivity. Thus far, the biochemical characterization of a membrane form of the molecule has not been reported. In a recent publication we demonstrated that murine IL-1 alpha can be detected in the supernatants of paraformaldehyde-treated macrophages. These data indicate that the phenomenon of membrane IL-1 may result from leakage of IL-1 from inadequately fixed cells. In the current report we have extended our studies toward the examination of human IL-1 alpha and IL-1 beta. IL-1 activity can be detected in the supernatants of paraformaldehyde-treated human monocytes. Although anti-IL-1 alpha, but not anti-IL-1 beta, antibodies can efficiently block the IL-1 bioactivity, both IL-1 alpha and IL-1 beta can be found by immunoprecipitation in the supernatants of the fixed monocytes. IL-1 alpha is efficiently processed to the low m.w. form, whereas IL-1 beta remains predominantly as the inactive, precursor molecule. IL-1 is not found in the supernatants of monocyte membrane preparations, demonstrating that the leakage of IL-1 is from an intracellular, rather than membrane-bound source.

IL-1 secretion by macrophages. Enhancement of IL-1 secretion and processing by calcium ionophores

In the present study we have demonstrated that the murine IL-1 alpha precursor lacks a cleavable signal sequence and does not undergo cotranslational translocation across microsomal membranes in vitro. Culture supernatants of the murine macrophage cell line, P388D, or from normal peritoneal macrophages collected within 0.5 to 3 h after stimulation contained the 33,000 m.w. precursor as the predominant form of IL-1 alpha. Over an 18-h period, the level of low m.w. IL-1 alpha increased as the secreted precursor was processed by extracellular and/or cell surface-associated proteolytic enzymes. The calcium ionophores A23187 and ionomycin were found to dramatically enhance the release and processing of murine and human IL-1. The rapid release of IL-1 in response to a change in the intracellular level of calcium does not appear to be caused by release of a membrane-bound form of the protein, nor is there evidence that IL-1 is packaged and released from cytoskeletal associated secretory granules. In marked contrast, calcium ionophores do not induce secretion of IL-1 from a nonmacrophage cell line that synthesizes but does not normally secrete IL-1. Our results suggest that activated macrophages possess a novel processing independent, possibly calcium-dependent, mechanism that allows for the release of the precursor forms of IL-1 alpha and IL-1 beta.

IL-1 secretion by macrophages. Enhancement of IL-1 secretion and processing by calcium ionophores

In the present study we have demonstrated that the murine IL-1 alpha precursor lacks a cleavable signal sequence and does not undergo cotranslational translocation across microsomal membranes in vitro. Culture supernatants of the murine macrophage cell line, P388D, or from normal peritoneal macrophages collected within 0.5 to 3 h after stimulation contained the 33,000 m.w. precursor as the predominant form of IL-1 alpha. Over an 18-h period, the level of low m.w. IL-1 alpha increased as the secreted precursor was processed by extracellular and/or cell surface-associated proteolytic enzymes. The calcium ionophores A23187 and ionomycin were found to dramatically enhance the release and processing of murine and human IL-1. The rapid release of IL-1 in response to a change in the intracellular level of calcium does not appear to be caused by release of a membrane-bound form of the protein, nor is there evidence that IL-1 is packaged and released from cytoskeletal associated secretory granules. In marked contrast, calcium ionophores do not induce secretion of IL-1 from a nonmacrophage cell line that synthesizes but does not normally secrete IL-1. Our results suggest that activated macrophages possess a novel processing independent, possibly calcium-dependent, mechanism that allows for the release of the precursor forms of IL-1 alpha and IL-1 beta.

The interleukins

The interactions between immune and inflammatory cells are mediated in large part by proteins, termed interleukins (IL), that are able to promote cell growth, differentiation, and functional activation. Seven interleukins have been described; each has unique biological activities as well as some that overlap with the others. Macrophages, cells that play important roles in both immunity and inflammation, produce IL 1 and IL 6, whereas T cells produce IL 2-IL 6 and bone marrow stromal cells produce IL 7. IL 1 and IL 6 not only play important roles in immune cell function, but also stimulate a spectrum of inflammatory cell types and induce fever. The growth and differentiation of eosinophils is markedly enhanced by IL 5. IL 2 is a potent proliferative signal for T cells, natural killer cells, and lymphokine-activated killer cells. IL 1, IL 3, IL 4, and IL 7 enhance the development of a variety of hematopoietic precursors. IL 4-IL 6 also serve to enhance B cell proliferation and antibody production. The understanding of interleukin structure and function has led to new and important insights into the fundamental biology of immunity and inflammation.

Partial purification of an immunosuppressive protein from a human tumor cell line and analysis of its relationship to transforming growth factor beta

The A673 human rhabdomyosarcoma cell line constitutively produces an acid-soluble, potent immunosuppressive factor (ISF), which inhibits T-cell proliferation. We have partially purified this factor from the culture supernatant of A673 cells by a sequence of acid extraction, gel filtration, cation exchange chromatography, and reverse-phase HPLC. Characterization studies indicate that ISF is similar or identical to transforming growth factor beta (TGF beta). ISF exhibits a molecular weight of 25 kDa in sodium dodecyl sulfate-polyacrylamide gels. ISF, like TGF beta, is a very basic protein (pI = 9.5) that is sensitive to reduction. Anti-TGF beta 1 antibodies completely block ISF activity in the thymocyte assay. Furthermore, ISF, like TGF beta, stimulated the anchorage-independent growth of normal rat kidney fibroblasts in soft agar.

Signal transduction pathway for IL-1. Involvement of a pertussis toxin-sensitive GTP-binding protein in the activation of adenylate cyclase

Human Il-1 alpha induces the synthesis of kappa Ig L chains by the pre-B cell line 7OZ/3, IL-2R alpha by the human NK cell line YT, and PGE2 by human rheumatoid synovial cells. Pertussis toxin (PT) markedly inhibited all three IL-1-induced activation events. The inhibition by PT was associated with a decrease in IL-1-mediated cAMP production. PT also inhibited IL-1-stimulated cAMP production in crude membrane fractions from 7OZ/3, YT, and 3T3 fibroblasts. In addition, IL-1 stimulated GTPase activity present in the membranes IL-1-responsive cells. Furthermore, the IL-1-induced GTPase activity was sensitive to PT. PT induced the ADP-ribosylation of a 46-kDa substrate in membrane preparations from IL-1-responsive cells. Cholera toxin also induced the ADP-ribosylation of a 46-kDa substrate in the same membrane preparations. The present findings indicate that the IL-1R is linked to a PT-sensitive G protein that stimulates the activity of adenylate cyclase.

Signal transduction pathway for IL-1. Involvement of a pertussis toxin-sensitive GTP-binding protein in the activation of adenylate cyclase

Human Il-1 alpha induces the synthesis of kappa Ig L chains by the pre-B cell line 7OZ/3, IL-2R alpha by the human NK cell line YT, and PGE2 by human rheumatoid synovial cells. Pertussis toxin (PT) markedly inhibited all three IL-1-induced activation events. The inhibition by PT was associated with a decrease in IL-1-mediated cAMP production. PT also inhibited IL-1-stimulated cAMP production in crude membrane fractions from 7OZ/3, YT, and 3T3 fibroblasts. In addition, IL-1 stimulated GTPase activity present in the membranes IL-1-responsive cells. Furthermore, the IL-1-induced GTPase activity was sensitive to PT. PT induced the ADP-ribosylation of a 46-kDa substrate in membrane preparations from IL-1-responsive cells. Cholera toxin also induced the ADP-ribosylation of a 46-kDa substrate in the same membrane preparations. The present findings indicate that the IL-1R is linked to a PT-sensitive G protein that stimulates the activity of adenylate cyclase.

In vitro activation and nuclear translocation of NF-kappa B catalyzed by cyclic AMP-dependent protein kinase and protein kinase C

We have examined whether a precursor form of NF-kappa B, a DNA-binding protein that plays a role in the transcriptional control of several genes, including kappa immunoglobulin light chain and interleukin-2 receptor alpha subunit, could be activated in vitro by protein kinases. DNA-binding activity of NF-kappa B was induced in the cytosolic fraction of unstimulated 70Z/3 murine pre-B cells by incubation with the catalytic subunit of cyclic AMP-dependent protein kinase (PKA) or protein kinase C (PKC). In contrast, PKA and PKC did not activate NF-kappa B in nuclear extracts from unstimulated cells. Identical results were obtained with the human natural killer-like cell line YT, which can be induced to express the interleukin-2 receptor alpha subunit in response to interleukin-1, cyclic AMP, or phorbol 12-myristate 13-acetate. Furthermore, when nuclei from unstimulated cells were incubated with PKA- or PKC-treated cytosolic fraction for 30 min at 30 degrees C, NF-kappa B was translocated into the nuclei. This translocation did not occur at 4 degrees C and was inhibited by wheat germ agglutinin but not by concanavalin A. Our findings support the conclusion that NF-kappa B exists in the cytoplasm of unstimulated cells in an inactive form that can be converted by exposure to PKA or PKC to an active DNA-binding form that can translocate to the nucleus.

Interleukin 1 and cyclic AMP induce kappa immunoglobulin light-chain expression via activation of an NF-kappa B-like DNA-binding protein

Interleukin 1 (IL-1) induces the synthesis of kappa immunoglobulin light chains and the expression of surface immunoglobulin in the murine pre-B-cell line 70Z/3 (J. G. Giri, P. W. Kincade, and S. B. Mizel, J. Immunol. 132:223-228, 1984). In the present study, we found that these effects of IL-1 are mimicked by cyclic AMP (cAMP) analogs and cAMP-elevating drugs. The induction of kappa immunoglobulin light-chain gene expression by IL-1 was associated with an increase in intracellular cAMP levels. Incubation of 70Z/3 cells with IL-1 or cAMP resulted in the activation of the kappa immunoglobulin enhancer, as detected by the induction of chloramphenicol acetyltransferase (CAT) in cells transfected with a kappa enhancer-CAT expression plasmid. In contrast, CAT plasmids lacking a kappa immunoglobulin enhancer were inactive in the presence of IL-1 or cAMP. Furthermore, IL-1 and cAMP analogs and inducers were found to induce the activation of a NF-kappa B-like DNA-binding protein that exhibited specificity for the kappa immunoglobulin enhancer. These results suggest that cAMP may play an important role as a second messenger for IL-1 in the induction of kappa immunoglobulin light-chain synthesis in pre-B cells via the activation of a DNA-binding protein that is similar or identical to NF-kappa B.

Evidence against the existence of a membrane form of murine IL-1 alpha

Previous studies have demonstrated that paraformaldehyde-treated macrophages possess IL-1 alpha activity in a variety of bioassay systems. However, no definitive biochemical data in support of the membrane IL-1 alpha concept has been reported. The purpose of the present study was to determine if the biologic activity associated with treated cells is due to a membrane form of IL-1 alpha or alternatively, to the leakage of IL-1 alpha. If the former case was true, then the exposed membrane IL-1 alpha should bind anti-IL-1 alpha antibodies or be cleaved by mild trypsin treatment. In both instances, IL-1 alpha activity should be lost when measured in a subsequent IL-1 bioassay. Our results indicate that pulsing paraformaldehyde-treated normal or cell line macrophages with anti-IL-1 alpha antibodies or treating the cells with trypsin did not affect the ability of the treated cells to function in a murine thymocyte proliferation assay. Furthermore, the standard short term treatment of cells with paraformaldehyde (15 min) did not prevent the leakage of IL-1 alpha from the cells or the processing of the precursor forms of the protein. When cells were treated with paraformaldehyde for 2 h, they no longer released IL-1 alpha or possessed thymocyte stimulatory activity. We also found that short term glutaraldehyde treatment of macrophages completely blocked the release of IL-1 alpha from cells as well as the appearance of cell-associated IL-1 alpha activity. Our results support the conclusion that the stimulatory activity of paraformaldehyde-treated macrophages is not due to a membrane form of IL-1 alpha but is, in fact, due to the continuous release of IL-1 alpha from the cells.

Evidence against the existence of a membrane form of murine IL-1 alpha

Previous studies have demonstrated that paraformaldehyde-treated macrophages possess IL-1 alpha activity in a variety of bioassay systems. However, no definitive biochemical data in support of the membrane IL-1 alpha concept has been reported. The purpose of the present study was to determine if the biologic activity associated with treated cells is due to a membrane form of IL-1 alpha or alternatively, to the leakage of IL-1 alpha. If the former case was true, then the exposed membrane IL-1 alpha should bind anti-IL-1 alpha antibodies or be cleaved by mild trypsin treatment. In both instances, IL-1 alpha activity should be lost when measured in a subsequent IL-1 bioassay. Our results indicate that pulsing paraformaldehyde-treated normal or cell line macrophages with anti-IL-1 alpha antibodies or treating the cells with trypsin did not affect the ability of the treated cells to function in a murine thymocyte proliferation assay. Furthermore, the standard short term treatment of cells with paraformaldehyde (15 min) did not prevent the leakage of IL-1 alpha from the cells or the processing of the precursor forms of the protein. When cells were treated with paraformaldehyde for 2 h, they no longer released IL-1 alpha or possessed thymocyte stimulatory activity. We also found that short term glutaraldehyde treatment of macrophages completely blocked the release of IL-1 alpha from cells as well as the appearance of cell-associated IL-1 alpha activity. Our results support the conclusion that the stimulatory activity of paraformaldehyde-treated macrophages is not due to a membrane form of IL-1 alpha but is, in fact, due to the continuous release of IL-1 alpha from the cells.

Cyclic AMP--an intracellular second messenger for interleukin 1

We demonstrated that interleukin 1 (IL-1), a potent peptide mediator in immune and inflammatory responses, stimulates the synthesis of cAMP in a variety of IL-1-responsive cell targets. We also showed that cAMP analogs and cAMP-inducing agents can replace IL-1 in the induction of interleukin 2 receptors on lymphocytes as well as in phytohemagglutinin-induced murine thymocyte proliferation. By use of IL-1 and the cAMP-inducer, forskolin, a direct correlation between the induced level of cAMP and the degree of lymphocyte interleukin 2 receptor expression or thymocyte proliferation was established. Our results indicate that cAMP may be an important intracellular second messenger for IL-1.

Characterization of the human interleukin 1 receptor on human polymorphonuclear leukocytes

Interleukin 1 (IL-1) is a mediator of inflammation with multiple proinflammatory and immunologic enhancing activities. Human polymorphonuclear leukocytes (PMN) also play a major role in the inflammatory response. We have found that PMN possess a single type of high affinity receptor for human recombinant (r) IL-1 alpha with an apparent dissociation constant of 0.28 nM. Approximately 700 receptors are present per cell. Binding is rapid with 50% of maximal binding occurring within 20 min at 4 degrees C. Internalization of the receptor occurs within 25 min after shifting the cells to 37 degrees C. The receptor exhibits an apparent molecular weight of approximately 60-70 kDa. Electron microscopic autoradiography studies reveal that the 125I-rIL-1 alpha localized in the nucleus within 180 min after shifting cells to 37 degrees C. The accumulation of relatively high levels of 125I-rIL-1 alpha in the nucleus is consistent with earlier observations on the nuclear localization of IL-1 in T lymphocytes. The possibility that IL-1 may exert a direct action in the nucleus remains to be determined.

Down-regulation of interleukin 1 production by macrophages of sarcoma-bearing mice

Peritoneal macrophages from mice bearing a transplantable methylcholanthrene-induced sarcoma produced progressively less IL 1 as tumor burden increased. The loss of activity was not explained by the production of any inhibitor of the mouse thymocyte comitogen bioassay. Immune precipitation with a polyclonal antibody confirmed the decline in IL 1 appearance. Although tumor-bearing animals lost approximately 17% of their carcass mass, the reduced production of IL 1 was not satisfactorily explained by coexistent malnutrition, since similarly depleted non-tumor-bearing mice were capable of producing IL 1. In addition to an altered IL 1 production by macrophages of tumor-bearing mice, SDS-polyacrylamide gel electrophoresis and autoradiography revealed that the pattern of secretory protein synthesis from LPS-stimulated and unstimulated peritoneal macrophages differed between tumor-bearing and control animals. Administration of LPS to tumor-bearing mice early after tumor transplantation resulted in reduced tumor growth and prevented the down-regulation of in vitro IL 1 production by peritoneal macrophages. These findings demonstrate a specific defect in IL 1 production associated with increasing tumor burden. Further studies are required to determine whether this defect in IL 1 synthesis contributes to the increased tumor growth.

Down-regulation of interleukin 1 production by macrophages of sarcoma-bearing mice

Peritoneal macrophages from mice bearing a transplantable methylcholanthrene-induced sarcoma produced progressively less IL 1 as tumor burden increased. The loss of activity was not explained by the production of any inhibitor of the mouse thymocyte comitogen bioassay. Immune precipitation with a polyclonal antibody confirmed the decline in IL 1 appearance. Although tumor-bearing animals lost approximately 17% of their carcass mass, the reduced production of IL 1 was not satisfactorily explained by coexistent malnutrition, since similarly depleted non-tumor-bearing mice were capable of producing IL 1. In addition to an altered IL 1 production by macrophages of tumor-bearing mice, SDS-polyacrylamide gel electrophoresis and autoradiography revealed that the pattern of secretory protein synthesis from LPS-stimulated and unstimulated peritoneal macrophages differed between tumor-bearing and control animals. Administration of LPS to tumor-bearing mice early after tumor transplantation resulted in reduced tumor growth and prevented the down-regulation of in vitro IL 1 production by peritoneal macrophages. These findings demonstrate a specific defect in IL 1 production associated with increasing tumor burden. Further studies are required to determine whether this defect in IL 1 synthesis contributes to the increased tumor growth.

The interleukin 1 receptor. Dynamics of interleukin 1 binding and internalization in T cells and fibroblasts

In this study, we have demonstrated that a murine T cell lymphoma, EL 4, and a murine fibroblast cell line, Swiss 3T3, possess a single class of high affinity interleukin 1 (IL 1) receptors that exist in a dynamic state of equilibrium that is influenced by IL 1. In the absence of IL 1, the IL 1 receptor appears to turnover with a t1/2 of approximately 11 hr. However, when cells are incubated in the presence of IL 1, the IL 1 receptor undergoes extensive ligand-induced down-regulation. IL 1 itself is internalized at 37 degrees C; 50% of the surface-bound IL 1 is internalized in 60 to 120 min. IL 1 does not undergo degradation for at least 6 hr after internalization. By using electron microscopy and autoradiography, we observed several important features of the internalization process. When cells having bound 125I-IL 1 at 4 degrees C were shifted to 37 degrees C, IL 1 moved from the cell membrane to the cytoplasm where it was found in proximity to nuclei or within lysosomes. IL 1 appeared to progressively accumulate in nuclei. Six hours after shifting cells to 37 degrees C, 30 to 35% of the internalized 125I-IL 1 is associated with the cell nucleus. The accumulation of relatively high levels of IL 1 in the nucleus raises the interesting possibility that IL 1 may not only interact in a highly specific manner with cell surface receptors, but also with potentially important nuclear receptors.

The interleukin 1 receptor. Dynamics of interleukin 1 binding and internalization in T cells and fibroblasts

In this study, we have demonstrated that a murine T cell lymphoma, EL 4, and a murine fibroblast cell line, Swiss 3T3, possess a single class of high affinity interleukin 1 (IL 1) receptors that exist in a dynamic state of equilibrium that is influenced by IL 1. In the absence of IL 1, the IL 1 receptor appears to turnover with a t1/2 of approximately 11 hr. However, when cells are incubated in the presence of IL 1, the IL 1 receptor undergoes extensive ligand-induced down-regulation. IL 1 itself is internalized at 37 degrees C; 50% of the surface-bound IL 1 is internalized in 60 to 120 min. IL 1 does not undergo degradation for at least 6 hr after internalization. By using electron microscopy and autoradiography, we observed several important features of the internalization process. When cells having bound 125I-IL 1 at 4 degrees C were shifted to 37 degrees C, IL 1 moved from the cell membrane to the cytoplasm where it was found in proximity to nuclei or within lysosomes. IL 1 appeared to progressively accumulate in nuclei. Six hours after shifting cells to 37 degrees C, 30 to 35% of the internalized 125I-IL 1 is associated with the cell nucleus. The accumulation of relatively high levels of IL 1 in the nucleus raises the interesting possibility that IL 1 may not only interact in a highly specific manner with cell surface receptors, but also with potentially important nuclear receptors.

Regulation of lipoprotein lipase synthesis and 3T3-L1 adipocyte metabolism by recombinant interleukin 1

When fully differentiated 3T3-L1 adipocytes were exposed to purified, recombinant murine interleukin 1 (rIL-1), a dose-dependent suppression of lipoprotein lipase activity was observed. The loss of activity reached a maximum of 60-70% of control and appeared to be due to an effect on the synthesis of the enzyme as judged by a suppression of the ability to incorporate [35S]methionine into immunoprecipitable lipoprotein lipase. There was no general effect on protein synthesis as determined by radiolabel incorporation into acid precipitable protein; however, after a 17 h exposure of the 3T3-L1 cells to recombinant interleukin 1, the synthesis of two proteins (molecular weights, 19,400 and 165,000 daltons) was enhanced several-fold. When the effect of Il-1 on the major metabolic pathways of the adipocyte was investigated, lipolysis as measured by glycerol release from the cells was markedly enhanced after a 17 h incubation with the hormone, while no effect was observed on de novo fatty acid synthesis. These effects on the metabolism of the adipocytes occur at concentration on a basis of molecules per cell, similar (only a 3-fold difference) to those required for stimulation of [3H]thymidine incorporation into mouse thymocyte DNA, suggesting that IL-1 may be a physiologically significant effector of adipocyte metabolism.

Structure-function analysis of murine interleukin 1: biologically active polypeptides are at least 127 amino acids long and are derived from the carboxyl terminus of a 270-amino acid precursor

Murine interleukin 1 (IL-1) is initially synthesized as a 270-amino acid precursor protein. Guided by amino-terminal end sequence analyses of mouse macrophage-derived IL-1, it was shown that expression of the carboxyl-terminal 156 amino acids (i.e., amino acids 115-270) of this precursor in Escherichia coli yields biologically active recombinant IL-1 (rIL-1) protein. To answer questions about precursor processing and the size of the smallest biologically active IL-1 fragment, we have engineered deletions of the rIL-1 (115-270) gene to encode two amino-terminal deletion analogs, rIL-1 (131-270) and rIL-1 (144-270), and a carboxyl-terminal deletion analog, rIL-1 (131-257, 270). The analogs were produced in E. coli, purified to homogeneity, and assayed for biological activity on murine thymocytes, human rheumatoid synovial cells, and human dermal fibroblasts and for their ability to bind to IL-1 receptors on murine EL-4 thymoma cells. The amino-terminal deletion analog rIL-1 (131-270) possessed a specific activity in the murine thymocyte proliferation assay equivalent to that of the 115-270 parent protein and exhibited significant biological activity in stimulating the production of collagenase and prostaglandin E2 by synovial cells and fibroblasts. The more extensive amino-terminal deletion analog rIL-1 (144-270) was inactive in all biological assays and failed to compete in the receptor binding assay. The carboxyl-terminal deletion analog rIL-1 (131-257, 270) competed less efficiently (by a factor of 100) in the receptor binding assay, retained weak biological activity on synovial cells and fibroblasts, and only demonstrated full intrinsic activity in the thymocyte proliferation assay when 100-200 times more protein was assayed. These results suggest that biologically active murine IL-1 polypeptides are at least 127 amino acids long and are derived from the carboxyl terminus of the 270-amino acid precursor. Furthermore, it appears that the integrity of the carboxyl terminus of the 270-amino acid precursor is important for activity but that different amino termini can be utilized to generate molecules with equivalent specific activities. This amino-terminal end flexibility supports a processing model for IL-1 maturation that partially explains IL-1 polypeptide heterogeneity.

I-A-positive nonlymphoid cells and T cell development in murine fetal thymus organ cultures: interleukin 1 circumvents the block in T cell differentiation induced by monoclonal anti-I-A antibodies

A fetal thymus organ culture system has been used to monitor the influence of interleukin 1 (IL 1) on the production of functional T cells as assessed by cell recoveries and MLC assays. We had shown earlier that the addition of monoclonal anti-I-A antibody inhibited the development of functional T cells as well as the expression of Ia on nonlymphoid cells recovered from fetal thymus organ cultures. The addition of purified recombinant IL 1 to anti-I-A-treated cultures reversed the inhibition of T cell growth induced by anti-I-A. IL 1 also induced the reexpression of Ia on the surfaces of nonlymphoid cells that could be recovered from the cultures. The "rescue" effect of IL 1 on anti-I-A-treated fetal thymus lobes was manifested in spite of the fact that the addition of IL 1 to untreated cultures had little effect on T cell development. To determine if IL 1 had a physiologic role in the development of the fetal thymus in organ culture, highly specific goat antibodies to IL 1 were added to organ cultures. These antibodies inhibited the development of T cells in organ cultures as determined by cell recovery and MLC reactivity. These results are consistent with the conclusion that IL 1 is an important mediator in the growth and development of functional T cells in the fetal thymus.

I-A-positive nonlymphoid cells and T cell development in murine fetal thymus organ cultures: interleukin 1 circumvents the block in T cell differentiation induced by monoclonal anti-I-A antibodies

A fetal thymus organ culture system has been used to monitor the influence of interleukin 1 (IL 1) on the production of functional T cells as assessed by cell recoveries and MLC assays. We had shown earlier that the addition of monoclonal anti-I-A antibody inhibited the development of functional T cells as well as the expression of Ia on nonlymphoid cells recovered from fetal thymus organ cultures. The addition of purified recombinant IL 1 to anti-I-A-treated cultures reversed the inhibition of T cell growth induced by anti-I-A. IL 1 also induced the reexpression of Ia on the surfaces of nonlymphoid cells that could be recovered from the cultures. The "rescue" effect of IL 1 on anti-I-A-treated fetal thymus lobes was manifested in spite of the fact that the addition of IL 1 to untreated cultures had little effect on T cell development. To determine if IL 1 had a physiologic role in the development of the fetal thymus in organ culture, highly specific goat antibodies to IL 1 were added to organ cultures. These antibodies inhibited the development of T cells in organ cultures as determined by cell recovery and MLC reactivity. These results are consistent with the conclusion that IL 1 is an important mediator in the growth and development of functional T cells in the fetal thymus.

Interleukin 1 alpha and interleukin 1 beta bind to the same receptor on T cells

Pure, E. coli-derived recombinant murine interleukin 1 alpha (IL 1 alpha) was labeled with 125I and used for receptor binding studies. The 125I-IL 1 binds to murine EL-4 thymoma cells in a specific and saturable manner. Scatchard plot analysis for binding studies carried out at 4 degrees C reveals a single type of high affinity binding site with an apparent dissociation constant of approximately 2.6 X 10(-10) M and the presence of approximately 1200 binding sites per cell. The rate of association of the 125I-IL 1 with EL-4 cells is slow, requiring more than 3 h to reach apparent steady state at 4 degrees C. Cell-bound 125I-IL 1 cannot be dissociated from EL-4 cells upon removal of unbound 125I-IL 1 and incubation of the cells at 4 degrees C in the presence or absence of unlabeled IL 1. Unlabeled recombinant murine IL 1 competes for 125I-IL 1 binding in a dose-dependent manner, whereas interferon-alpha A, interleukin 2 (IL 2), epidermal growth factor, and nerve growth factor have no effect. The 125I-IL 1 binding site is sensitive to trypsin, suggesting that it is localized on the cell surface. We have also examined the ability of purified recombinant human IL 1 alpha and IL 1 beta to compete for binding of the radiolabeled murine IL 1 to its receptor and to stimulate IL 2 production by EL-4 cells. Previous reports have shown that human IL 1 alpha is approximately 60% homologous in amino acid sequence with murine IL 1, but that human IL 1 beta is only about 25% homologous with either murine IL 1 or human IL 1 alpha. Despite these marked differences, however, we report here that both human IL 1 proteins are able to recognize the same binding site as mouse IL 1. In addition, murine as well as both human IL 1 proteins stimulate IL 2 production by EL-4 cells.

Interleukin 1 alpha and interleukin 1 beta bind to the same receptor on T cells

Pure, E. coli-derived recombinant murine interleukin 1 alpha (IL 1 alpha) was labeled with 125I and used for receptor binding studies. The 125I-IL 1 binds to murine EL-4 thymoma cells in a specific and saturable manner. Scatchard plot analysis for binding studies carried out at 4 degrees C reveals a single type of high affinity binding site with an apparent dissociation constant of approximately 2.6 X 10(-10) M and the presence of approximately 1200 binding sites per cell. The rate of association of the 125I-IL 1 with EL-4 cells is slow, requiring more than 3 h to reach apparent steady state at 4 degrees C. Cell-bound 125I-IL 1 cannot be dissociated from EL-4 cells upon removal of unbound 125I-IL 1 and incubation of the cells at 4 degrees C in the presence or absence of unlabeled IL 1. Unlabeled recombinant murine IL 1 competes for 125I-IL 1 binding in a dose-dependent manner, whereas interferon-alpha A, interleukin 2 (IL 2), epidermal growth factor, and nerve growth factor have no effect. The 125I-IL 1 binding site is sensitive to trypsin, suggesting that it is localized on the cell surface. We have also examined the ability of purified recombinant human IL 1 alpha and IL 1 beta to compete for binding of the radiolabeled murine IL 1 to its receptor and to stimulate IL 2 production by EL-4 cells. Previous reports have shown that human IL 1 alpha is approximately 60% homologous in amino acid sequence with murine IL 1, but that human IL 1 beta is only about 25% homologous with either murine IL 1 or human IL 1 alpha. Despite these marked differences, however, we report here that both human IL 1 proteins are able to recognize the same binding site as mouse IL 1. In addition, murine as well as both human IL 1 proteins stimulate IL 2 production by EL-4 cells.

Regulation of class III major histocompatibility complex gene products by interleukin-1

Interleukin-1 (IL-1) is a product of mononuclear phagocytes that mediates changes characteristic of the response to inflammation or tissue injury (the acute-phase response). One of two structurally and functionally homologous major histocompatibility complex (MHC) class III genes encodes a positive acute-phase protein, complement factor B. The closely linked complement C2 gene is not affected during the acute-phase response. Purified human IL-1, pH 7.0, and recombinant-generated murine IL-1, pH 5.0, increased the expression of factor B and other positive acute-phase proteins in human hepatoma cells but decreased the expression of albumin, a negative acute-phase reactant. Furthermore, in a murine fibroblast L-cell line transfected with cosmid DNA bearing the human C2 and factor B genes, IL-1 mediated a reversible dose- and time-dependent increase in factor B expression in the transfected cells. Expression of the C2 gene was not affected by IL-1. The effect of IL-1 on factor B expression involves a mechanism acting at a pre-translational level as demonstrated by an increase in specific messenger RNA content and a corresponding increase in biosynthesis and secretion of factor B. The structural basis and mechanism for selective and independent regulation of these genes provides insight into the molecular control of the inflammatory response.

Immunoregulatory molecules and IL 2 receptors identified in multiple sclerosis brain

Frozen brain specimens from eight multiple sclerosis (MS) patients were examined for the presence of leukocytes and their cell products by using a panel of monoclonal antibodies. The results presented here demonstrated that in the MS lesion, there was a marked accumulation of HLA-Dr-positive (Ia-positive) cells. These Ia-positive cells were identified as being glial fibrillary acidic protein positive by using double staining methods. Furthermore, the cells in the MS lesion expressed the interleukin 2 (IL 2) receptor, as identified by the anti-TAC monoclonal antibody. The cells in the region of the plaque also exhibited positive staining with antibodies to IL 1, IL 2, and prostaglandin E. Neither normal brain nor brain specimens from progressive multifocal leukoencephalopathy or Alzheimer's disease showed such patterns of staining. These results suggest that stimulated cells are present in the MS brain, thus implicating an active immune mechanism in the pathogenesis of MS.

Immunoregulatory molecules and IL 2 receptors identified in multiple sclerosis brain

Frozen brain specimens from eight multiple sclerosis (MS) patients were examined for the presence of leukocytes and their cell products by using a panel of monoclonal antibodies. The results presented here demonstrated that in the MS lesion, there was a marked accumulation of HLA-Dr-positive (Ia-positive) cells. These Ia-positive cells were identified as being glial fibrillary acidic protein positive by using double staining methods. Furthermore, the cells in the MS lesion expressed the interleukin 2 (IL 2) receptor, as identified by the anti-TAC monoclonal antibody. The cells in the region of the plaque also exhibited positive staining with antibodies to IL 1, IL 2, and prostaglandin E. Neither normal brain nor brain specimens from progressive multifocal leukoencephalopathy or Alzheimer's disease showed such patterns of staining. These results suggest that stimulated cells are present in the MS brain, thus implicating an active immune mechanism in the pathogenesis of MS.

In vivo inflammatory activity of epidermal cell-derived thymocyte activating factor and recombinant interleukin 1 in the mouse

Epidermal cell-derived thymocyte activating factor (ETAF), a cytokine produced by keratinocytes, has previously been shown to be biochemically and functionally very similar, if not identical, to interleukin 1 (IL-1). Both ETAF and IL-1 have been demonstrated to be chemotactic for neutrophils and mononuclear cells in vitro. In order to demonstrate that this activity has physiological relevance we have used a simple in vivo model. The present study demonstrates that injection of high-titer ETAF or purified recombinant murine IL-1 into the mouse footpad results in an influx of neutrophils into the site with peak accumulation at 4 h. Footpad swelling also occurs with a time course roughly paralleling that of the neutrophil accumulation. Injection of control proteins failed to reproduce this phenomenon. Margination of neutrophils within blood vessels was seen within 1 h of injection of ETAF or IL-1, followed by entry into the stroma by 4 h. This suggests that chemotactic activity and not merely increased adherence or inhibition of migration is occurring. 5-10 d of daily, subcutaneous injection of ETAF on the mouse flank resulted in an infiltrate of neutrophils, and to a lesser degree, mononuclear cells in association with epidermal hyperplasia, subcutaneous fibrosis, and focal muscle necrosis in the panniculus carnosus. These findings were not seen in control sites injected with media. These findings provide direct in vivo experimental evidence suggesting a physiologic role for ETAF/IL-1 in local inflammation.

Stimulation of fibroblast proliferation and prostaglandin production by purified recombinant murine interleukin 1

Recombinant murine interleukin 1 (IL-1) obtained from a clone of Escherichia coli containing an IL-1 expression plasmid was purified to homogeneity using a sequential extraction procedure and gel filtration chromatography. The purified recombinant IL-1 exhibited a pI of approximately 5.2 and a sp act of 6 X 10(6) units/mg. These values are in agreement with those obtained with natural murine IL-1. The purified recombinant IL-1 enhanced the proliferation of human HEL and WI-38 fibroblasts in a serum-free medium. In addition, IL-1 stimulated fibroblast PGE2 5- to 30-fold over a 24-hr period. The effects of IL-1 on fibroblast activation were obtained with the same concentrations of IL-1 that are effective in the mouse thymocyte assay. These results unequivocally establish the ability of IL-1 to modulate fibroblast proliferation and function.

The role of IL 1 in the antigen-specific activation of murine class II-restricted T lymphocyte clones

The role of IL 1 in the antigen-specific activation of class II-restricted T lymphocytes was examined by using a model system consisting of cloned WEHI 5 B lymphoma accessory cells and class II-restricted, soluble antigen- or alloantigen-reactive T cell clones. The addition of exogenous recombinant IL 1 to the T cell cultures resulted in a significant enhancement of the antigen-specific T cell proliferation response, but at best, only small increases in IL 2 release. Goat IgG anti-IL 1 antibodies were added to the T cell cultures to assess their effect on T cell activation. The IL 1 enhancement of the T cell proliferation response was inhibited by the anti-IL 1 antibodies in a dose-dependent manner. In contrast, only modest levels (10 to 25%) of proliferation inhibition were observed in T cell cultures containing either WEHI 5 or splenocyte accessory cells but no exogenous IL 1. When the anti-IL 1 antibodies were added to primary mixed lymphocyte cultures stimulated by WEHI 5 cells in the absence of exogenous IL 1, no significant inhibition of proliferation was observed. A small but statistically significant proliferation inhibition was observed when anti-IL 1 antibodies were added to mixed lymphocyte reaction cultures stimulated by splenocytes. Two-color cytofluorometric analysis of the effects of IL 1 on antigen-activated T cell clones demonstrated that under suboptimal stimulation conditions, IL 1 stimulated a small but significant increase in the number of T cells bearing IL 2 receptors. In the presence of optimal numbers of WEHI 5 accessory cells, IL 1 enhanced T cell proliferation in the absence of a detectable increase in the number of T cells bearing IL 2 receptors, the number of IL 2 receptors per T cell, or the levels of IL 2 released. Finally, exogenous IL 1 can be added as late as 18 to 24 hr after culture initiation without significantly reducing its ability to enhance the T cell proliferation response. These data indicate that IL 1 has pleiotropic effects on murine T lymphocytes and can function to enhance T cell activation at multiple points during the activation sequence.