Virus infection activates IL-1 beta and IL-18 production in human macrophages by a caspase-1-dependent pathway.

Monocytes and macrophages play a significant role in host's defense system, since they produce a number of cytokines in response to microbial infections. We have studied IL-1 beta, IL-18, IFN-alpha/beta, and TNF-alpha gene expression and protein production in human primary monocytes and GM-CSF-differentiated macrophages during influenza A and Sendai virus infections. Virus-infected monocytes released only small amounts of IL-1 beta or IL-18 protein, whereas 7- and 14-day-old GM-CSF-differentiated macrophages readily produced these cytokines. Constitutive expression of proIL-18 was seen in monocytes and macrophages, and the expression of it was enhanced during monocyte/macrophage differentiation. Expression of IL-18 mRNA was clearly induced only by Sendai virus, whereas both influenza A and Sendai viruses induced IL-1 beta mRNA expression. Since caspase-1 is known to cleave proIL-1 beta and proIL-18 into their mature, active forms, we analyzed the effect of a specific caspase-1 inhibitor on virus-induced IL-1 beta and IL-18 production. The release of IL-1 beta and IL-18, but not that of IFN-alpha/beta or TNF-alpha, was clearly blocked by the inhibitor. Our results suggest that the cellular differentiation is a crucial factor that affects the capacity of monocytes/macrophages to produce IL-1 beta and IL-18 in response to virus infections. Furthermore, the virus-induced activation of caspase-1 is required for the efficient production of biologically active IL-1 beta and IL-18.     

A soluble binding protein specific for interleukin 1 beta is produced by activated mononuclear cells

Soluble interleukin 1 (IL 1) binding proteins were identified by gel filtration and covalent cross-linking of 125I IL 1 in normal human serum and inflammatory exudate. High molecular weight 125I IL 1 protein complexes occurred with both IL 1 alpha and IL 1 beta, however, high molecular weight binding appeared to be non-specific. One specific IL 1 beta binding protein was observed to elute at approximately 100 kDa on gel filtration when bound to 125I IL 1 beta. This complex migrated as a broad band at 60 kDa when covalently cross-linked and analyzed by SDS-PAGE. The protein did not bind 125I IL 1 alpha and 125I IL 1 beta binding was only displaceable by excess cold IL-1 beta. The production of the specific IL 1 beta binding protein was assessed in a number of cell populations. Unstimulated peripheral blood mononuclear cells (PBMNC) did not produce the binding protein, but stimulation with phytohemagglutinin (PHA) caused production within 24 hr and binding protein levels remained elevated for up to 7 days. Stimulation with lipopolysaccharide (LPS) and IL 1 alpha did not consistently induce synthesis of the binding protein. Ligand-binding studies were performed to compare solubilized EL 4 NOB.1 cell membrane IL 1 receptor (sIL 1R) with semi-purified IL 1 beta binding protein from pooled synovial fluid. The sIL 1R preparation bound ligand with an affinity of 168 pM while the IL 1 beta binding protein bound 125I IL 1 beta with an affinity of 370 pM. This protein may function as an important carrier molecule for IL 1 beta and determine its distribution and kinetics in vivo.     

Cloning and structural analysis of cDNA coding for human prointerleukin-1 alpha and prointerleukin-1 beta

The data are presented on the cloning and structural analysis of the cDNA coding for human prointerleukin-1 alpha and prointerleukin-1 beta (proIL-1 alpha and proIL-1 beta). The nucleotide sequences of proIL-1 alpha and proIL-1 beta cDNAs have been compared with the sequences published earlier. The nucleotide changes resulting in the aminoacid changes of the protein were not found. Some nucleotide changes were identified within the 3'-nontranslated region of the proIL-1 beta cDNA. The existence of the allelic variants for interleukin genes registered only on the gene level has been supposed.     

TLR-independent induction of human monocyte IL-1 by phosphoglycolipids from thermophilic bacteria

The structures of phosphoglycolipids PGL1 and PGL2 from the thermophilic bacteria Meiothermus taiwanensis, Meiothermus ruber, Thermus thermophilus, and Thermus oshimai are determined recently (Yang et al. in J Lipid Res. 47:1823-1932, 2006). These bacteria belong to Gram-negative bacteria that do not contain lipopolysaccharide, but high amounts of phosphoglycolipids and glycoglycerolipids. Here we show that PGL1/PGL2 mixture (PGL1: PGL2 = 10:1 ~ 10:2) from M. taiwanensis and T. oshimai, but not T. thermophilus and M. ruber, up-regulate interleukin-1beta (IL-1beta) production in human THP-1 monocytes and blood-isolated primary monocytes. PGL2 was purified after phospholipase A2 hydrolysis of PGL1 in the PGL1/PGL2 mixture followed by column chromatography. PGL2 did not induce proIL-1 production, even, partially (35-40%) inhibited PGL1-mediated proIL-1 production, showing that PGL1 is the main inducer of proIL-1 production in PGL1/PGL2 mixture. The production of proIL-1 stimulated by phosphoglycolipids was strongly inhibited by specific PKC-alpha, MEK1/2, and JNK inhibitors, but not by p38-specific inhibitor. The intracellular calcium influx was involved in phosphoglycolipids-mediated proIL-1 production. Using blocking antibody and Toll-like receptor (TLR)-linked NF-kappaB luciferase assays, we found that the cellular receptor(s) for phosphoglycolipids on proIL-1 production was TLR-independent. Further, phosphoglycolipids isolated from T. thermophilus and M. ruber did not induce proIL-1 production, even though T. thermophilus possess more PGL1 than PGL2 (6:4). Specially, the fatty acid composition of phosphoglycolipids from both T. thermophilus and M. ruber consists of a low percentage of C15 (<10%) and a high percentage of C17 (>75%). It suggests, the C15 percentage of PGL may play a critical role in PGL-mediated proIL-1 induction.     

Two distinct monokines, interleukin 1 and tumor necrosis factor, each independently induce biosynthesis and transient expression of the same antigen on the surface of cultured human vascular endothelial cells

A murine monoclonal antibody (H4/18) raised against cultured human endothelial cells (HEC) prestimulated by the monokine interleukin 1 (IL 1) recognizes a cell surface molecule inducible by IL 1 or by the distinct monokine tumor necrosis factor (TNF) in primary or serially passaged HEC. H4/18 binding is not basally expressed or inducible by IL 1 in an SV-40 transformed HEC line, in human dermal fibroblasts, or in blood leukocytes. Expression of this molecule by HEC in response to IL 1 can be blocked by protein and RNA synthesis inhibitors but not by cyclooxygenase inhibitors. In addition, H4/18 can immunoprecipitate two biosynthetically labeled polypeptides (Mr 100,000 and 120,000) from HEC stimulated with IL 1 but not from control HEC. Thus, the H4/18 binding site appears to be an inducible surface protein specific for HEC. The majority of HEC in a culture can be induced to express the H4/18 binding protein, but expression is transient (peak 4 to 6 hr) and over the next 24 hr declines to near basal levels either in the continued presence of or upon removal of IL 1. The magnitude of the peak response depends upon IL 1 concentration (peak 5 to 10 U/ml), and the response is optimized by the continued presence of IL 1 during the initial 4- to 6-hr induction period. The time of peak H4/18 binding does not appear to be a function of IL 1 concentration. The decline of H4/18 binding from peak levels is prevented by cycloheximide, a protein synthesis inhibitor. HEC maintained in the presence of IL 1 for 24 hr become refractory to restimulation by IL 1; however, IL 1-stimulated cells rested in the absence of IL 1 for 20 hr can be stimulated by fresh IL 1. HEC expression of the H4/18 binding protein is not induced by interleukin 2 or by interferon-alpha, -beta, or -gamma. Induction of H4/18 binding by TNF is also concentration dependent, transient, and dependent upon protein and RNA synthesis. Several observations suggest that IL1 and TNF act independently on HEC. Our TNF is a recombinant protein, expressed from a cloned cDNA and thus free of IL 1 contamination; it also has no activity in a highly sensitive IL 1 assay. Our standard IL 1 preparation is affinity purified and lacks TNF activity on L929 cells. Thus, our monokine preparations are not cross-contaminated. Most interestingly, HEC incubated with IL 1 and refractory to IL1 restimulation can be restimulated by TNF to express H4/18 binding and vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)     

Febrile temperatures attenuate IL-1 beta release by inhibiting proteolytic processing of the proform and influence Th1/Th2 balance by favoring Th2 cytokines

We investigated possible feedback mechanisms of febrile temperatures on LPS- and staphylococcal enterotoxin B (SEB)-induced cytokine release in human whole blood. LPS-induced IL-1beta release was inhibited at temperatures >38 degrees C, whereas intracellular proIL-1beta formation as well as the release of other cytokines except IL-18 were only attenuated above 42 degrees C, indicating that febrile temperatures impair the proteolytic processing of proIL-1beta. This attenuated processing is not due to either heat inactivation of caspase-1 or structural changes in proIL-1beta produced at higher temperatures. Instead, we propose that febrile conditions change cytosolic compartmentation or trafficking, so that synthesized proIL-1beta cannot encounter caspase-1. Febrile temperatures also influenced Th1/Th2 cytokine balance. We observed a 3-fold increase in the Th2-cytokines IL-5 and IL-13 and a reduction to 15% of the Th1-cytokine IL-2 when SEB-stimulated whole blood was incubated at 40 degrees C compared with 37 degrees C. These results indicate that fever limits the production of the fever-inducing IL-1beta and also influences the adaptive immune response, favoring Th2 cytokine production.     

The secretory route of the leaderless protein interleukin 1beta involves exocytosis of endolysosome-related vesicles

Interleukin 1beta (IL-1beta), a secretory protein lacking a signal peptide, does not follow the classical endoplasmic reticulum-to-Golgi pathway of secretion. Here we provide the evidence for a "leaderless" secretory route that uses regulated exocytosis of preterminal endocytic vesicles to transport cytosolic IL-1beta out of the cell. Indeed, although most of the IL-1beta precursor (proIL-1beta) localizes in the cytosol of activated human monocytes, a fraction is contained within vesicles that cofractionate with late endosomes and early lysosomes on Percoll density gradients and display ultrastructural features and markers typical of these organelles. The observation of organelles positive for both IL-1beta and the endolysosomal hydrolase cathepsin D or for both IL-1beta and the lysosomal marker Lamp-1 further suggests that they belong to the preterminal endocytic compartment. In addition, similarly to lysosomal hydrolases, secretion of IL-1beta is induced by acidotropic drugs. Treatment of monocytes with the sulfonylurea glibenclamide inhibits both IL-1beta secretion and vesicular accumulation, suggesting that this drug prevents the translocation of proIL-1beta from the cytosol into the vesicles. A high concentration of extracellular ATP and hypotonic medium increase secretion of IL-1beta but deplete the vesicular proIL-1beta content, indicating that exocytosis of proIL-1beta-containing vesicles is regulated by ATP and osmotic conditions.     

The inflammasome: a molecular platform triggering activation of inflammatory caspases and processing of proIL-beta

Generation of Interleukin (IL)-1beta via cleavage of its proform requires the activity of caspase-1 (and caspase-11 in mice), but the mechanism involved in the activation of the proinflammatory caspases remains elusive. Here we report the identification of a caspase-activating complex that we call the inflammasome. The inflammasome comprises caspase-1, caspase-5, Pycard/Asc, and NALP1, a Pyrin domain-containing protein sharing structural homology with NODs. Using a cell-free system, we show that proinflammatory caspase activation and proIL-1beta processing is lost upon prior immunodepletion of Pycard. Moreover, expression of a dominant-negative form of Pycard in differentiated THP-1 cells blocks proIL-1beta maturation and activation of inflammatory caspases induced by LPS in vivo. Thus, the inflammasome constitutes an important arm of the innate immunity.