Modulation of fibroblast functions by interleukin 1: increased steady- state accumulation of type I procollagen messenger RNAs and stimulation of other functions but not chemotaxis by human recombinant interleukin 1 alpha and beta

Interleukin-1 (IL-1) is synthesized by and released from macrophages in response to a variety of stimuli and appears to play an essential role in virtually all inflammatory conditions. In tissues of mesenchymal origin (e.g., cartilage, muscle, bone, and soft connective tissue) IL-1 induces changes characteristic of both destructive as well as reparative phenomena. Previous studies with natural IL-1 of varying degrees of purity have suggested that it is capable of modulating a number of biological activities of fibroblasts. We have compared the effects of purified human recombinant (hr) IL-1 alpha and beta on several fibroblast functions. The parameters studied include cell proliferation, chemotaxis, and production of collagen, collagenase, tissue inhibitor of metalloproteinase (TIMP), and prostaglandin (PG) E2. We observed that hrIL-1s stimulate the synthesis and accumulation of type I procollagen chains. Intracellular degradation of collagen is not altered by the hrIL-1s. Both IL-1s were observed to increase the steady-state levels of pro alpha 1(I) and pro alpha 2(I) mRNAs, indicating that they exert control of type I procollagen gene expression at the pretranslational level. We found that both hrIL-1 alpha and beta stimulate synthesis of TIMP, collagenase, PGE2, and growth of fibroblasts in vitro but are not chemotactic for fibroblasts. Although hrIl-1 alpha and beta both are able to stimulate production of PGE2 by fibroblasts, inhibition of prostaglandin synthesis by indomethacin has no measurable effect on the ability of the IL-1s to stimulate cell growth or production of collagen and collagenase. Each of the IL-1s stimulated proliferation and collagen production by fibroblasts to a similar degree, however hrIL-1 beta was found to be less potent than hrIL-1 alpha in stimulating PGE2 production. These observations support the notion that IL-1 alpha and beta may both modulate the degradation of collagen at sites of tissue injury by virtue of their ability to stimulate collagenase and PGE2 production by fibroblasts. Furthermore, IL-1 alpha and beta might also direct reparative functions of fibroblasts by stimulating their proliferation and synthesis of collagen and TIMP.     

Blocking the interleukin-1 receptor inhibits leukotriene B4 and prostaglandin E2 generation in human monocyte cultures.

Interleukin-1 is a potent stimulator of arachidonic acid (AA) metabolism and this activity could be attributed to the activation of the prostaglandin-forming enzyme cyclooxygenase or of the arachidonic-releasing enzyme phospholipase A2 or both. Prostaglandin E2 (PGE2), a cyclooxygenase product, and LTB4 (5-(S),12-(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid), a lipoxygenase product, are potent mediators of inflammation. Recently a new cytokine produced by macrophages and named interleukin-1 receptor antagonist (IL-1ra) (MW 22,000 Da) which specifically binds and blocks IL-1 receptors, has proven to be a potent inflammatory inhibitor. In our studies we found that monocyte suspensions, pretreated with hrIL-1ra at increasing concentrations (0.25-250 ng/ml) for 10 min and then treated with LPS in an overnight incubation inhibits, in a dose-dependent manner, the generation of LTB4 as measured by the highly sensitive radioimmunoassay method. In monocytes pretreated with hrIL-1ra (250 ng/ml) for 10 min and treated with arachidonic acid (10(-5)-10(-9) M) and LPS overnight, the release of LTB4 was partially inhibited when compared to hrIL-1ra-untreated cells. Moreover, hrIL-1ra (250 ng/ml) caused a partial inhibition of monocyte LTB4 production when the cells were activated with AA (10(-7) M) and then treated with IL-1 beta (5 ng/ml) overnight or 24 hr incubation. In addition, human monocytes pretreated for 10 min with increasing doses of hrIL-1ra (0.25-250 ng/ml) and then treated with hrIL-1 alpha (5 ng/ml) or beta (5 ng/ml) for 18 hr, also resulted in the inhibition of PGE2 generation as measured by RIA when compared with hrIL-1ra-untreated cells. When the cells were treated with hrIL-1ra (250 ng/ml) and activated for 18 and 48 hr with increasing doses of hrIL-1 beta a strong inhibitory effect was found on PGE2 production. HrIL-1ra used at 15 ng/ml gave a partial inhibition of LTB4 generation, after LPS (1-100 ng/ml) treatment, while NDGA totally blocked the production of LTB4. Moreover, PGE2 released by macrophages activated with LPS (100 ng/ml) or hrIL-1 beta (5 ng/ml) at 18 hr incubation time was strongly inhibited when hrIL-1ra (250 ng/ml) was used. These data suggest that the inhibition of LTB4 and PGE2 by this new macrophage-derived monokine IL-1ra occurs through the block of the IL-1 receptor, rather than phospholipase A2, and thus IL-1ra may offer a potential therapeutic approach to inflammatory states.     

Comparison of human interleukin-1 beta and its 163-171 peptide in bone resorption and the immune response

Human interleukin-1 beta (IL-1 beta) caused a dose- and time-dependent enhancement of the release of 45Ca from prelabeled mouse calvaria in organ culture. In addition, IL-1 beta dose-dependently stimulated the formation of prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha in the calvarial bones. However, IL-1 beta-induced 45Ca release was only partially inhibited by blocking the PGE2 response with indomethacin, suggesting that enhanced PGE2 formation in response to IL-1 beta is not necessary to obtain a bone resorptive effect, but that prostaglandins potentiate the action of IL-1 beta. The synthetic nonapeptide VQGEESNDK, corresponding to the fragment 163-171 of human IL-1 beta, administered simultaneously with antigen (SRBC) to C3H/HeN male mice, induced a dose-dependent enhancement of specific antibody-producing cells in the spleen (PFC). The degree of PFC stimulation was comparable to that caused by native human IL-1 beta. In mouse bone cultures, neither 45Ca release nor prostanoid formation was stimulated by fragment 163-171. These data indicate that (1) IL-1 beta-induced stimulation of bone resorption is dissociable from IL-1 beta-induced increase of prostanoid biosynthesis and (2) the epitope of the IL-1 beta molecule involved in the immunostimulatory effects may be different from that involved in the stimulatory effects on bone resorption.     

Chromosomal location of murine and human IL-1 receptor genes.

The gene for the type I interleukin-1 (IL-1) receptor has been mapped in both mouse and human. In the human genome, a combination of segregation analysis of rodent-human hybrid cells and chromosomal in situ hybridization has placed the gene on the long arm of chromosome 2, at band 2q12. This is near the reported map position of the loci for IL-1 alpha and IL-1 beta (2q13----2q21). The murine gene has been mapped by analysis of restriction fragment length polymorphisms in interspecific backcrosses to the centromeric end of chromosome 1, in a region that is syntenic to a portion of human chromosome 2. The murine Il-1r1 gene has thus been separated from the IL-1 genes, which lie on murine chromosome 2.     

Presence of IL-1 receptors on human and murine neutrophils. Relevance to IL-1-mediated effects in inflammation

Inflammatory responses are characterized by the infiltration of polymorphonuclear neutrophils (PMN) at the involved site. IL-1 may have an important role in mediating this response, but whether IL-1 acts directly on PMN is controversial. In this study, we examined PMN for the presence of IL-1R and determined the effect of IL-1 on PMN migration in vivo. Thioglycollate, proteose-peptone, or IL-1 elicited peritoneal exudate cells were found to bind 125I-IL-1 alpha in a specific and saturable manner. This binding was localized to the PMN in the exudate. Scatchard plot analysis indicates the presence of approximately 1700 receptors per PMN and an apparent dissociation constant of 3.0 x 10(-10) M. Binding sites for 125I-IL-1 alpha were also found on human PMN prepared from peripheral blood. There are approximately 900 receptors per cell on human PMN with a dissociation constant similar to that observed for elicited murine PMN. Binding of 125I-IL-1 alpha to the mouse and human PMN is inhibited by both recombinant human IL-1 alpha and IL-1 beta, indicating that both IL-1 proteins bind to the same receptor on these cells. Human PMN were able to internalize radioiodinated IL-1. We conclude that PMN possess receptors for IL-1 and that these binding sites may be important in mediating IL-1 effects on granulocytes that are involved in the inflammatory response.     

In vivo immunostimulating activity of the 163-171 peptide of human IL-1 beta

The stimulating effect of a synthetic nonapeptide (fragment 163-171) of human interleukin 1 beta (IL-1 beta) on antibody responses to both T helper-dependent and T helper-independent antigens was investigated. It was shown that the nonapeptide enhanced the antibody response, as evaluated in the hemolytic plaque assay, of spleen cells from mice immunized with sheep red blood cells (SRBC). The activity of the 163-171 peptide on the primary response to SRBC was dose-dependent, being maximal when the peptide was inoculated at 100 mg/kg together with the antigen. Moreover, the 163-171 peptide was also effective in enhancing the secondary response to SRBC. The effect of the 163-171 peptide was to augment the frequency of cells specific for the antigen, inasmuch as no increase was ever observed in spleen cell numbers after treatment. In all these studies, human recombinant IL-1 beta gave effects qualitatively comparable to those of the 163-171 peptide, with a maximal activity at 20 ng/kg. Both the 163-171 peptide and human recombinant IL-1 beta were also able to enhance the in vivo immune response to a T helper-independent antigen such as SIII, a poorly immunogenic polysaccharidic antigen from Streptococcus pneumoniae type III. It can therefore be proposed that this synthetic nonapeptide of human IL-1 beta may represent a good candidate for use as adjuvant in vaccines.     

Heterogeneity in interleukin (IL)-1 receptors expressed on human B cell lines. Differences in the molecular properties of IL-1 alpha and IL-1 beta binding sites

IL-1 alpha and IL-1 beta although distantly related at the primary sequence level, bind to the same Mr 80,000 IL-1 receptor on various cell types. Several lines of evidence indicate, however, that the IL-1 receptor on B cells and T cells differ. By binding experiments with 125I-IL-1, marked heterogeneity in IL-1 receptor binding was observed in 13 of 24 B cell lines studied. This was classified into three categories: (I) in nine cell lines, 125I-IL-1 alpha binding revealed high (kD = 10(-10) M) and low affinity (kD = 10(-8) M) IL-1 alpha receptors, whereas 125I-IL-1 beta binding showed one class only with intermediate affinity (kD = 10(-9) M); (II) in three cell lines selective binding with 125I-IL-1 beta was observed; (III) in one cell line only, 125IL-1 alpha and 125I-IL-1 beta bind to a single class of IL-1 receptors as has been described for most cell types. Cross-linking with 125I-IL-1 alpha or 125I-IL-1 beta demonstrated their specific binding to Mr 80,000 and to Mr 68,000 in cell lines in categories I and III, whereas for those in category II, binding to the IL-1 receptor was confined to 125I-IL-1 beta. The expression of two subsets of IL-1 alpha receptors but only one class of IL-1 beta receptors was further confirmed in kinetic studies. Internalization at 37 degrees C demonstrated that only 19% of IL-1 beta was internalized and that binding with IL-1 alpha was entirely cell surface. Flow cytometry studies showed that IL-1 alpha and IL-1 beta do not influence B cell surface antigen expression, suggesting that the ability of IL-1 to influence B cell proliferation is not mediated via direct binding to the IL-1 receptor only.     

Expression of IL-1 receptors on human peripheral B cells

The expression of IL-1R on human peripheral B cells was analyzed by the binding assay with 125I-labeled human rIL-1 alpha and by the flow cytofluorometry by the use of FITC-conjugated IL-1 alpha. The proliferation and the differentiation of B cells stimulated with Staphylococcus aureus Cowan I (SAC) in the presence of T cell-derived factors were dependent on IL-1. By the binding experiment with 125I-labeled IL-1 alpha, B cells expressed only few IL-1R without any stimulations. When they were stimulated with SAC, IL-1R on B cells began to increase by only 1 h, reached the maximum level at 6 h. The binding of 125I-labeled IL-1 alpha to B cells was inhibited by the addition of either cold IL-1 alpha or IL-1 beta suggesting that IL-1R on B cells reactive for IL-1 alpha and IL-1 beta were identical. By Scatchard plot analysis, the existence of two classes of IL-1R on B cells was found. A major class of IL-1R (320 molecules/cell) has a lower affinity (Kd = 3.8 x 10(-10) M) and a minor class of IL-1R (70 molecules/cell) has a higher affinity (Kd = 4.4 x 10(-12) M). When B cells were stimulated with SAC, both lower and higher affinity IL-1R were increased to 1960 molecules/cell and 300 molecules/cell, respectively. Furthermore, IL-1R on B cells were also detected with FITC-conjugated IL-1 alpha by a flow cytofluorometer. Only 3 to 5% of B cells expressed IL-1R without any stimulations. When B cells were stimulated with SAC, IL-1R-positive B cells were increased to 20%. The addition of anti-class II antibodies inhibited B cell proliferation and differentiation induced with SAC, IL-1, and T cell-derived factors. Anti-class II antibodies also inhibited the number of IL-1R on B cells. These results suggest that the expression of IL-1R was induced as the initial stage of B cell activation and that class II Ag play an important role for the expression of IL-1R on B cells.     

Activated human Langerhans cells express mRNA for IL-1 alpha and IL-1 beta and produce these cytokines but do not secrete them.

Human Langerhans cells (LC) were isolated from epidermal cell preparations by panning with mouse anti-CD1 monoclonal antibody. RNA was prepared and probed for the presence of mRNAs for various cytokines using radiolabeled cDNAs. After stimulation with phorbol myristate acetate LC express RNA for interleukin 1 alpha (IL-1 alpha) and interleukin 1 beta (IL-1 beta) and produce proteins but do not secrete them at detectable levels. LC-associated IL-1, particularly IL-1 alpha, may play a role in antigen presentation. PMA did not induce IL-6 expression in LC. The addition of lipopolysaccharide, a muramyl dipeptide analog, ionomycin, IL-1 alpha, tumor necrosis factor-alpha, insulin-like growth factor-1 or IL-6 did not induce IL-1 mRNA in LC. UVB augmented IL-1 beta mRNA expression. Glucocorticoids did not detectably affect IL-1 alpha or IL-1 beta mRNA levels following PMA induction, however, staurosporin inhibited IL-1 beta mRNA synthesis. Thus the inducers and regulators of IL-1 formation in human LC and monocytes are not identical.     

Characterization and detection of naturally occurring antibodies against IL-1 alpha and IL-1 beta in normal human plasma.

During the development and testing of a radioreceptor assay (RRA) for human IL-1, we have detected and identified the presence of auto-antibodies to IL-1 in normal human plasma (NHP). The RRA is based on the competition between human 125I-labeled rIL-1 alpha and standard or unknown quantities of IL-1 alpha or IL-1 beta for binding to a limited amounts of IL-1 receptor (IL-1R) isolated from the EL4 mouse thymoma cell line. NHP from 20 out of 100 unselected blood donors were found to completely inhibit the binding of 125I-labeled IL-1 alpha to its receptor, suggesting the presence in these NHP samples of either abnormal amounts of IL-1 or of a factor binding to the 125I-labeled IL-1 alpha. Special care was taken to ascertain that the inhibitory factors were antibodies and not soluble IL-1 receptor antagonist. When plasma samples with inhibiting activity were incubated with labeled IL-1 alpha and chromatographed on a Sephadex G200 column, they were found to contain 125I-labeled complexes with an apparent molecular weight of 150-200kD. The IL-1 binding factor could be eliminated from plasma by incubation with protein A-Sepharose, suggesting that it consisted in IgG antibodies directed against IL-1. Furthermore, the antibody nature of the inhibiting factor was confirmed by its binding to purified rIL-1 coupled to Sepharose. Screening of 200 NHP samples by incubation with 100 pg of 125I-labeled IL-1 followed by precipitation with 12% of polyethylene glycol (PEG) confirmed that about 25% of NHP contain detectable IgG antibodies to IL-1 alpha, while only 2% of NHP contain antibodies to IL-1 beta. No correlation between the presence of these anti-IL-1 antibodies and any particular major histocompatibility complex or any pathological conditions was detected. We suggest that all serum samples assayed for IL-1 alpha or IL-1 beta content should be pretested with the PEG precipitation assay described here.     

Development of glycosylated human interleukin-1 alpha, neoglyco IL-1 alpha, by coupling with D-galactose monosaccharide: biological activities in vitro

In the previous study, galactose with C9 spacer was chemically coupled to human recombinant (rh) IL-1 alpha in order to study the effect of glycosylation on its activities, and to develop IL-1 with less deleterious effects. In this study we examined a variety of IL-1 activities in vitro, including proliferative effect on T cells, antiproliferative effect on myeloid leukemic cells and melanoma cells, stimulatory effects on IL-6 synthesis by melanoma cells and PGE2 synthesis by fibroblast cells Galactose-introduced IL-1 alpha (Gal-IL-1 alpha) exhibited reduced activities from 10 to 10000 times compared with unmodified IL-1 alpha in all the activities performed in vitro. The competitive binding of 125I-IL-1 alpha to mouse T cells and pre-B cells with unlabeled IL-1 alpha s suggests a decrease in binding affinities of Gal-IL-1 alpha to both type I and type II IL-1 receptors. Therefore, reduced activities of Gal-IL-1 alpha are due, at least partially, to the decrease in their receptor binding affinities.     

HepG2 cells predominantly express the type II interleukin 1 receptor (biochemical and molecular characterization of the IL-1 receptor).

In this study we have characterized the cell surface interleukin 1 (IL-1) receptor in HepG2 hepatoma cells. We found that HepG2 cells bind both IL-1 alpha and beta with high affinity, KDs of 136 and 180 pM and receptor densities of 16,000 and 8500 binding sites/cell respectively. The binding sites appeared to be predominantly type II since phorbol ester treatment of the cells, which selectively downregulates type II IL-1 receptors, reduced binding by 68% while treatment of the cells with an inhibitory monoclonal antibody specific for the type I receptor had no significant effect on IL-1 binding. Competition studies with a modified IL-1 beta analog (Glu4) also revealed binding kinetics more consistent with binding to type II receptors than to type I. Crosslinking and ligand blotting with human 125I-IL-1 demonstrated the presence of two bands, a 78 kDa band typical of crosslinking to type II (p60) receptor, and a 98 kDa band, typical of crosslinking to the type I (p80) receptor. Low level expression of the type I receptor was consistent with molecular biological studies employing polymerase chain reaction (PCR) amplification which indicated that mRNA for the type I receptor was produced by the HepG2 cells. Functional receptors were demonstrated by the induction of IL-8 by IL-1 stimulated cells.     

Effect of berberrubine on interleukin-8 and monocyte chemotactic protein-1 expression in human retinal pigment epithelial cell line

We examined the effects of berberrubine, a protoberberine alkaloid, on interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) expression in a human retinal pigment epithelial cell line (ARPE-19) stimulated with interleukin-1beta (IL-1beta) or tumor necrosis factor alpha (TNF-alpha). ARPE-19 cells were cultured to confluence. Berberrubine and IL-1beta or TNF-alpha were added to the medium. IL-8 and MCP-1 protein concentrations were measured using enzyme-linked immunosorbent assay. IL-8 and MCP-1 mRNA were measured by real time polymerase chain reaction. Nuclear factor kappaB (NF-kappaB) translocation was examined by immunofluorescent staining/microscopy. Berberrubine dose-dependently inhibited IL-8 and MCP-1 protein levels in the media and mRNA expression of the cells stimulated with IL-1beta or TNF-alpha. Immunofluorescent staining/microscopy of NF-kappaB in the nucleus of unstimulated cells was faint (51+/-14 arbitrary units). Fluorescein was dense (215+/-42 or 170+/-24 arbitrary units, respectively) 30 min after stimulation with IL-1beta or TNF-alpha and was decreased to 62+/-18 or 47+/-16 arbitrary units, respectively, by berberrubine. Berberrubine dose-dependently inhibited IL-8 and MCP-1 expression and protein secretion induced by IL-1beta or TNF-alpha. Possibly, the effect on chemotactic factors may be via suppression of NF-kappaB translocation.     

IL-1beta-mediated proinflammatory responses are inhibited by estradiol via down-regulation of IL-1 receptor type I in uterine epithelial cells

The objective of this study was to examine the effects of sex hormones on IL-1beta-mediated responses by uterine epithelial cells. The mRNA expression and secretion of human beta-defensin-2 and CXCL8 by uterine epithelial cells was examined following stimulation with IL-1beta in the presence of estradiol or progesterone. Estradiol inhibited the IL-1beta-mediated mRNA expression and secretion of human beta-defensin-2 and CXCL8 by uterine epithelial cells while progesterone had no effect. Inhibition of the IL-1beta-mediated response by estradiol was dose dependent, with maximal inhibition observed using 10(-7) to 10(-10) M, and was shown to be mediated through the estrogen receptor because addition of a pure estrogen receptor antagonist abrogated this effect. The mechanism by which estradiol inhibits IL-1beta-mediated responses by uterine epithelial cells appears to be the down-modulation of the IL-1R type I, thereby reducing the uterine epithelial cell's ability to respond to IL-1beta. These results suggest that the inhibitory effect of estradiol on IL-1beta-mediated inflammatory responses by uterine epithelial cells indicates a link between the endocrine and immune systems and may be crucial for dampening proinflammatory responses during the time of ovulation or pregnancy.     

Interleukin-1 receptor antagonist binds to the type II interleukin-1 receptor on B cells and neutrophils.

We have examined the binding of human and rodent interleukin-1 receptor antagonist (IL-1ra) to the type II IL-1 receptor on the human B cell line, Raji, on the mouse pre-B cell line, 70Z/3, and on human polymorphonuclear leukocytes (PMNs). Human IL-1ra binds to the receptors on the human B cells with an affinity (KD = 15 +/- 3 nM) equal to that of IL-1 alpha and only 15-fold lower than that of IL-1 beta and, likewise, binds to human PMNs with an affinity (KD = 8 +/- 4 nM) 15-fold lower than that of IL-1 beta. Mouse and rat IL-1ra bind to these two human cell types with an affinity similar to that of the human protein. Human IL-1ra binds very weakly to the type II receptor on the mouse pre-B cells with an affinity (KD = 1.4 +/- 0.2 microM) about 1500-fold lower than human IL-1 beta. Mouse and rat IL-1ra also bind to the mouse pre-B cells with low affinity. The weak binding of the three IL-1ra proteins to these mouse cells appears to be more a consequence of the cell type rather than species specificity. There may be a population of cells for which the actions of IL-1 cannot be effectively opposed by IL-1ra, although this group does not include mature B cells and PMNs.     

Phosphorylation of intracellular precursors of human IL-1

The human IL-1 molecules (IL-1 alpha and IL-1 beta) are post-translationally cleaved from 31-kDa precursor to 18-kDa biologically active molecules. During the course of studies of post-translational modifications of human IL-1, we have observed that although LPS induced the production of both intracellular IL-1 alpha and IL-1 beta in human monocytes, [32P]orthophosphate labeling of these cells revealed that intracellular precursor of IL-1 alpha (pre-IL-1 alpha) to be phosphorylated at least 10-fold more than intracellular pre-IL-1 beta. However, no 32P-incorporation could be detected in the 18-kDa processed IL-1 alpha and IL-1 beta. Analysis by TLC revealed that the major phosphorylation site occurred at serine residue(s). The 32P was incorporated into multiply cleaved precursors of IL-1 alpha, which appeared in the absence of protease inhibitors. Since the smallest Mr pre-IL-1 alpha that was labeled with 32P was 22 kDa, the phosphorylated serine residue is presumably located adjacent to a sequence of four basic amino acids located in the 4-kDa region at the amino terminus of the 22-kDa precursor of IL-1 alpha. This serine residue might also be a major phosphorylation site for a cAMP-dependent protein kinase. This hypothesis was substantiated by the demonstration that a synthetic peptide analogue of this region (residue 84 to 112) could be similarly phosphorylated in vitro by a cAMP-dependent protein kinase. Furthermore, a truncated pre-IL-1 alpha (residue 64 to 271) and a "fusion" protein containing staphylococcal protein A and an amino-terminal half-portion of pre-IL-1 alpha (residue 1 to 112), but not mature IL-1 alpha (residue 113 to 271), could also be phosphorylated by cAMP-dependent protein kinase. There is no comparable amino acid sequence in IL-1 beta which could be expected to be phosphorylated by a cAMP-dependent protein kinase. The physiologic relevance of phosphorylation of pre-IL-1 alpha was investigated. The data showed that phosphorylation of truncated pre-IL-1 alpha greatly enhanced its susceptibility to digestion by trypsin and promoted the conversion of pre-IL-1 alpha to the more biologically active IL-1. Although the precise role of the rather selective phosphorylation of pre-IL-1 alpha is not known, our findings do suggest that the phosphorylation of serine close to dibasic/tetrabasic amino acid sequence functions to facilitate the processing and/or release of IL-1 alpha.     

Presence of high affinity receptor for interleukin-1 (IL-1) on cultured porcine thyroid cells

Using 125I-interleukin-1 beta (125I-IL-1 beta) as a ligand, a specific receptor of high affinity dissociation constant (1.1 +/- 0.2 x 10(-10) M) with binding sites (350 +/- 40/cell) for interleukin-1 beta (IL-1 beta) has been demonstrated on cultured porcine thyroid cells. IL-1 alpha almost equally cross-reacted with the receptor (Kd = 1.2 +/- 0.3 x 10(-10) M and 350 +/- 50 binding sites/cell). TSH, IL-2 and other peptide hormones did not inhibit the binding of 125I-IL-1 beta to thyroid cells. Crosslinking study revealed a major band (approximately 95 kD) with a corrected molecular mass of approximately 78 kD. Moreover, both IL-1 beta and IL-1 alpha stimulated prostaglandin E2 production of cultured porcine thyroid cells, although the potency of IL-1 alpha was slightly greater than that of IL-1 beta. These results suggest that IL-1 may be involved in the regulation of thyroid cell function.     

Reversal of autocrine and paracrine effects of interleukin 1 (IL-1) in human arthritis by type II IL-1 decoy receptor. Potential for pharmacological intervention

Interleukin 1 (IL-1), produced by both synovial cells and chondrocytes, plays a pivotal role in the pathogenesis of cartilage destruction in osteoarthritis (OA). We examined the specific expression and function of IL-1 receptor family-related genes in human joint tissues. Gene array analysis of human normal and OA-affected cartilage showed mRNA expression of IL-1 receptor accessory protein (IL-1RAcp) and IL-1 type I receptor (IL-1RI), but not IL-1 antagonist (IL-1ra) and IL-1 type II decoy receptor (IL-1RII). Similarly, human synovial and epithelial cells showed an absence of IL-1RII mRNA. Functional genomic analyses showed that soluble (s) IL-1RII, at picomolar concentrations, but not soluble TNF receptor:Fc, significantly inhibited IL-1beta-induced nitric oxide (NO) and/or prostaglandin E(2) production in chondrocytes, synovial and epithelial cells. In OA-affected cartilage, the IC(50) for inhibition of NO production by sIL-1RII was 2 log orders lower than that for sIL-1RI. Human chondrocytes that overexpressed IL-1RII were resistant to IL-1-induced IL-1beta mRNA accumulation and inhibition of proteoglycan synthesis. In osteoarthritis, deficient expression by chondrocytes of innate regulators or antagonists of IL-1 such as IL-1ra and IL-1RII (soluble or membrane form) may allow the catabolic effects of IL-1 to proceed unopposed. The sensitivity of IL-1 action to inhibition by sIL-1RII has therapeutic implications that could be directed toward correcting this unfavorable tissue(s) dependent imbalance.