The four biochemically distinct species of human interleukin 1 all exhibit similar biologic activities

The supernatants of human monocytes incubated with endotoxin are able to stimulate the proliferation of murine thymocytes in the presence of PHA. This is known as LAF (lymphocyte activating factor) activity and is a characteristic activity of interleukin 1 (IL 1). The LAF activity can be resolved into four major fractions: a 15,000 dalton (pI 7), a 15,000 (pI 5.5), a 35,000 (pI 7), and a 35,000 (pI 5.5) fraction. To determine whether these four fractions shared the other biologic activities ascribed to IL 1, they were compared in a series of bioassays. When standardized with respect to their LAF activities, the four fractions did not differ significantly as mitogens for murine thymocytes, inducers of IL 2, murine or human B cell activators, human chondrocyte or synoviocyte stimulants, or inducers of acute phase proteins in vivo. On the other hand, the samples differed markedly as stimulators of porcine synoviocytes, with the 15,000 dalton (pI 5.5) fraction being the only strongly active fraction. These results are consistent with the hypothesis that all four LAF could be products of a single gene, although the porcine receptor may be able to distinguish between them. If this is the case, all four fractions can properly be termed IL 1.

Identification of a membrane-associated interleukin 1 in macrophages

We have found a surface membrane-associated interleukin 1 (IL-1) with potent thymocyte and T-cell stimulatory activity on peptone-elicited peritoneal macrophages. The IL-1 activity was demonstrated on both fixed macrophage monolayers and on isolated membranes from unfixed macrophages. Membrane IL-1 was induced by adherence and/or by adding heat-killed Listeria monocytogenes to macrophage cultures. The macrophage membrane IL-1 was similar functionally and antigenically to soluble IL-1, but its expression could be temporally dissociated from IL-1 secretion; membrane IL-1 was induced earlier and persisted longer than IL-1 secretion during in vitro macrophage culture. Moreover, when cultured macrophages that had ceased both secretion and membrane expression of IL-1 were restimulated by adding heat-killed Listeria, substantial membrane IL-1 was induced in the absence of detectable IL-1 secretion. Membrane IL-1 appears to be an integral membrane protein since it was solubilized by detergent but was not eluted by EDTA, high salt, or low pH treatment of the membranes.

Partial purification of a factor from human synovium that possesses interleukin 1, chondrocyte stimulating and catabolin-like activities

Human synovial explants in culture release material that stimulates the production of prostaglandin E2 (PGE2) and several extracellular enzymes by human chondrocytes. Fractionation of conditioned medium by gel filtration revealed a protein of approx. 15 kDa, which in addition to stimulating production of PGE2 and plasminogen activator by human articular chondrocytes, possessed interleukin 1 activity and induced cartilage degradation. Further purification using iso-electric focussing again showed co-elution of these activities with a major pI of 6.9 and a minor pI of 5.1-5.3. This study indicated that human synovium releases a factor that is closely related to or identical with interleukin 1 and suggests that this protein may participate in cellular interactions that occur within the rheumatoid joint.

Studies on the synthesis and secretion of interleukin 1. I. A 33,000 molecular weight precursor for interleukin 1

Previous studies have suggested that murine interleukin 1 (IL 1) may be synthesized as a high m.w. precursor. Using specific antibodies against murine IL 1, we have analyzed the primary form of IL 1 synthesized by normal peritoneal macrophages and P388D1 cell line macrophages, and in vitro using poly (A)+ RNA from stimulated normal and cell line macrophages. In all cases, the labeled protein immunoprecipitated with the anti-IL 1 antibodies exhibited a m.w. of 33,000 on SDS gels. This 33,000 m.w. protein was not an aggregate of low m.w. IL 1. Addition of excess purified low m.w. IL 1 completely blocked the immunoprecipitation of the 33,000 m.w. protein. When cells were pulsed with [35S]methionine for 1 to 5 hr and then incubated in medium containing unlabeled methionine for 19 hr, labeled low m.w. IL 1 was detected in the culture fluid. If cells were pulsed with [35S]methionine to label the 33,000 m.w. protein and then incubated in the presence of a maximally effective concentration of the protein synthesis inhibitor, cycloheximide, the low m.w. IL 1 was still found in the culture fluid. Our results indicate that IL 1 is synthesized as a 33,000 m.w. precursor that is converted to the low m.w. form that is found in the culture fluid of stimulated murine macrophages.

Thymocyte activating factors from SV40-transformed human embryo fibroblasts

A novel factor was found in the medium conditioned by SV40-transformed human embryo fibroblasts, which stimulate concanavalin A-induced thymocyte DNA synthetic response. This activity was estimated to be 10-15 kD and divided into two activities by ion exchange chromatography. One of them is a protein molecule and the other is a glycoprotein. In addition, these activities are not derived from the growth factors reported previously such as interleukin 2 (Morgan, R., Ruscetti, F. and Gallo, R. C. (1976) Science 193, 1007-1008) and transforming growth factor (De Larco, J. E. and Todaro, G. J. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 4001-4005).

Purification to homogeneity of biologically active human interleukin 1

Human interleukin 1 (IL-1) produced by lipopolysaccharide-stimulated monocytes was purified to homogeneity with retention of biological activity. IL-1 was measured by its ability to enhance the proliferative response of thymocytes to phytohemagglutinin. The purification procedure included hydrophobic affinity chromatography on phenyl Sepharose, gel filtration through Ultrogel AcA54 and preparative isoelectric focusing. Both charged species of IL-1, pI 5.1 and 6.8 have a molecular weight of 14,500 as determined by SDS-polyacrylamide gel electrophoresis. The complete purification resulted in a recovery of approximately 0.01% of IL-1 protein and if protection against losses by denaturation and adsorption in the final purification step was provided by bovine serum albumin, approximately 11% of IL-1 activity can be recovered.

Generation of an interleukin-I-like lymphocyte-stimulating factor at inflammatory sites: correlation with the infiltration of polymorphonuclear leucocytes

Using a mouse thymocyte co-stimulation assay, we demonstrated thymocyte-stimulating activity in murine peritoneal fluid obtained from the early stage (3 to 9 h) of casein-induced inflammation. This early inflammatory stage coincided with the time at which an influx of polymorphonuclear leucocytes (PMN) into the inflamed site was observed. Similar thymocyte-stimulating activity was produced in vitro by PMN purified from 4-h peritoneal exudate but not by purified PMN obtained at a later stage (24 h) of the inflammation. The inflammatory factor was interleukin (IL)-I-like; it was devoid of IL-2 activity when tested with IL-2-dependent cells. It could stimulate murine thymocytes to produce IL-2. On a Sephadex G-75 column, the factor was eluted between the molecular sizes of 10 000 and 30 000; its peak activity was at 21 000. The factor mainly consisted of two (pI 6.5 and pI 5.0) iso-electrophoretically different factors.

Interleukin 1 enhances synovial cell hyaluronate synthesis

Interleukin 1 enhances proliferation of murine thymocytes in the presence of lectins, and is also known to stimulate the release of prostaglandins and neutral proteases from a variety of cell types. We have previously shown that a factor isolated from the culture media of disaggregated lining cells of the human synovial membrane was indistinguishable from monocyte-derived interleukin 1. We report here that interleukin 1 from either source stimulates hyaluronate synthesis by synovial membrane cells. Upon gel filtration or isoelectric focusing of synovial cell supernatants, the hyaluronate-stimulatory activity co-fractionates with the interleukin 1 activity. Enhanced cell secretion of hyaluronate is a newly described metabolic effect of interleukin 1.

Purification and partial biochemical characterization of normal human interleukin 1

A protocol for the rapid, efficient purification of the major charged species of human interleukin 1 (IL-1) has been developed using high performance anion exchange and size exclusion chromatography. The isolated material is pure as determined by sodium dodecyl sulfate (SDS) gradient polyacrylamide gel electrophoresis (PAGE) and analytical isoelectric focusing (IEF). The molecular weight of the purified material is 15,000 and the isoelectric point (pI) is 6.8, values that are in good agreement with those previously reported for human IL-1. 10(-10) M concentrations of the purified material give half-maximal stimulation in the thymocyte proliferation assay. Amounts of IL-1 sufficient for receptor studies and detailed biochemical analysis can now be produced on a regular basis.

Induction of fibroblast proliferation by interleukin-1 derived from human monocytic leukemia cells

Human interleukin-1 (IL-1), free of contaminating lymphokines, was isolated from cultures of purified monoblasts from a patient with acute monocytic leukemia. Partially purified IL-1 (diafiltration, ultrafiltration, and isoelectric focusing) stimulated proliferation of subconfluent human fibroblasts in vitro. Further purification of IL-1 by high-resolution gel filtration- and anion exchange-high performance liquid chromatography revealed that fibroblast proliferation activity could not be separated from IL-1 activity (thymocyte proliferation), suggesting that both activities are the properties of a single molecule. Fibroblasts and thymocytes exhibited a similar sensitivity to the proliferative effects of IL-1. These findings suggest that macrophages participating in inflammatory reactions in vivo might release IL-1, which could function to expand fibroblast populations at sites of inflammatory reactions, by acting as a fibroblast growth factor.

Lymphokines and monokines as regulators of human lymphoproliferation

The development of a competent immunoregulatory response in the face of an antigenic challenge is modulated by soluble proteins of relatively low molecular mass. Lymphokines and monokines, secreted by cells of T lineage and cells of the monocyte/microphage series, respectively, function in a bimodal amplification network that results in the proliferation and differentiation of the immunoregulatory cells. Interleukin 1 is typically assayed by its effect on thymocytes or by its ability to promote the T cell-dependent release of interleukin 2. Interleukin 2 is routinely measured by its ability to support the long-term growth of cultured T cells, whereas B cell growth factor is measured by its ability to support the long-term growth of cultured B lymphocytes. The availability of homogeneous purified factors and the subsequent availability of monoclonal antibodies against these reagents should allow for the development of rapid quantitative assays for these analytes in diverse biological fluids. In addition, large quantities of purified reagents will promote studies to determine therapeutic efficacy in several immunodeficiency syndromes.

Cleavage of human interleukin 1: isolation of a peptide fragment from plasma of febrile humans and activated monocytes

Interleukin 1 (IL 1) is a product(s) of mononuclear phagocytes, and has multiple biologic activities that mediate several host responses to infection and inflammation. Highly purified IL 1 activates lymphocytes, induces fever, increases hepatic acute phase protein synthesis, and increases muscle protein degradation. A 4.2 kd peptide has been purified from plasma of febrile humans which also induces muscle proteolysis in vitro (termed proteolysis-inducing factor, PIF). Because IL 1 purified from activated human monocytes induces muscle proteolysis in vitro, studies were performed to determine the relationship of human monocyte-derived IL 1 to plasma-derived PIF. Purified PIF was highly active in the IL 1 thymocyte assay. After gel filtration of plasma from febrile patients, fractions with PIF activity also induced thymocyte proliferation and fever in mice. Thus, it seems likely that the plasma peptide PIF has IL 1 properties and probably represents a small m.w. cleavage product of IL 1. Further studies confirmed this finding. Highly purified 15 kd IL 1, rechromatographed over different gel filtration media, consistently fragmented into a 4 kd peptide with both muscle proteolysis-inducing and lymphocyte-activating properties. The breakdown of the 15 kd IL 1 into biologically active smaller fragments increased with time, and could be accelerated by trypsinization. The monocyte-derived IL 1 fragments were partially destroyed by heat. Highly purified 125I-labeled 15 kd IL 1 also fragmented into subunits, and these radioactive subunits produced fever in mice and were active in the thymocyte assay. Fragmentation of 125I-labeled 15 kd IL 1 was reduced by agents that inhibit proteases. These results indicate that some of the biologic activities of human IL 1 are conserved in small m.w. fragments. These studies also provide evidence that IL 1 may circulate in humans as a 4.2 kd peptide, and that this cleavage product can function as an active mediator of IL 1 effects in the host.

Purification of human interleukin 1 by high-performance liquid chromatography

The utility of high-performance liquid chromatography (HPLC) in the purification of Interleukin 1 (IL 1, lymphocyte-activating factor) has been investigated Human IL 1-containing supernatants were concentrated by lyophilization and desalted using Bio-Gel P-6 DG desalting gel. Subsequently, the sample containing IL 1 activity was subjected to HPLC with a novel HPHT hydroxylapatite column. Using a sodium phosphate gradient, IL 1 was eluted as a single peak of activity separated from the major protein contaminant, yielding 90% recovery and a specific activity of 6.3 X 10(4) U/mg. Pooled fractions from Bio-Gel HPHT were concentrated and subjected either to Bio-Sil IEX 540 DEAE anion-exchange or Bio-Sil TSK 125 size exclusion chromatography. From DEAE the IL 1 activity was eluted before a linear sodium chloride gradient was started, whereas the protein contaminant was eluted at 110 mM NaCl. When TSK was used IL 1 activity was eluted within a molecular weight range of 20,000-10,000. Fractions from the DEAE or TSK columns that were positive for IL 1 activity did not contain detectable protein, suggesting a good resolution. Furthermore, the recovery from DEAE was 26% whereas TSK 125 yielded 119% of the original activity. The specific activities were 6 X 10(7) and 2.5 X 10(8) U/mg, respectively. Thus, this method provides a rapid and reproducible procedure for the purification if IL 1 for further biological characterization.

Interleukin 1 activity in normal human urine

Urine concentrates from normal individuals were shown to contain interleukin 1 (IL 1)-like activity when tested directly on human dermal fibroblasts and on C3H/HeJ mouse thymocytes in the presence of 1 microgram/ml phytohemagglutinin. Seventy-five percent of the urine samples tested, however, demonstrated the presence of a specific inhibitor of IL 1-promoted thymocyte proliferation. This inhibitor did not affect IL 2-promoted proliferation of mouse thymocytes or CT-6 cells or IL 1-promoted proliferation of human dermal fibroblasts. After gel filtration of the urine concentrates, even those samples that were inhibitory yielded fractions containing both thymocyte and fibroblast proliferative activity. The approximate m.w. of these activities were 75,000 and 15,000. In addition, two peaks of low m.w. thymocyte proliferative activity were noted at 4000 and 2000. The 2000 pool, but not the 4000 pool, also contained fibroblast proliferative activity.

Human lung macrophages enhance and inhibit lymphocyte proliferation

To evaluate the effector functions of human lung macrophages, cell preparations containing 70 to 95% macrophages were obtained from surgically resected lungs of cancer patients and were co-cultured with allogeneic or autologous peripheral blood mononuclear cells (PBMC) and Con A. In contrast to previous reports of either marked stimulatory or inhibitory effects of human lung macrophages on lymphocyte function, the present results demonstrate that the proliferative response was a complex function of both the numbers of PBMC and macrophages. In the presence of low numbers of PBMC, small numbers of macrophages enhanced proliferation, whereas larger numbers inhibited proliferation; in the presence of larger numbers of PBMC, macrophages only inhibited. Inhibition was not mediated by cyclo-oxygenase products of arachidonic acid metabolism, because indomethacin did not reverse it. The enhancing effect of macrophages was greater when tested with PBMC depleted of monocytes. Lung macrophages were 10-fold more potent in mediating enhancement than corresponding numbers of peripheral blood monocytes. Both the enhancing and the inhibitory activities could be reproduced by lung macrophage lysates or supernatants derived from macrophages cultured in serum-free medium. Macrophages cultured at high density yielded inhibitory supernatants, which on dilution resulted in enhancing activity. The enhancing activity appeared in supernatants maximally after 24 hr, and its appearance was not inhibited by culturing macrophages in the presence by culturing macrophages in the presence of cycloheximide. Sephacryl S-200 chromatography of such supernatants yielded two peaks of enhancing activity, with apparent m.w. of 160,000 and 40,000, which we call lung macrophage-derived lymphocyte-activating factors (LM-LAF). Fractions with LM-LAF activity contained no IL 1 activity (assessed by augmentation of mitogen-induced proliferation of mouse thymocytes), but IL 1 activity was present in a peak of m.w. of 15,000. The 15,000 m.w. fraction did not enhance the proliferation of human PBMC. These results demonstrate that human lung macrophages are potent modulators of lectin-mediated proliferation of human PBMC. The effects are mediated in part by the release of soluble, pre-formed factors that appear to be distinct from previously described monokines.

Induction of human interleukin-1 by a product of Staphylococcus aureus associated with toxic shock syndrome

Certain strains of Staphylococcus aureus associated with toxic shock syndrome elaborate material that induces human blood monocytes to secrete interleukin-1 (IL-1). IL-1 was detected both by its ability to cause fever in rabbits using the leukocytic pyrogen (LP) assay and by its mitogenic activity towards thymocytes in the so-called lymphocyte-activating factor (LAF) assay. Anti-human IL-1 prevents the manifestation of both activities. Filtrates of control strains of S. aureus manifest neither activity. Thus, culture filtrates derived from toxic shock syndrome (TSS)-associated strains cause biphasic fever in rabbits when injected intravenously. The fever lasts several hours. Plasma taken at the peak of the fever and injected into a second set of rabbits produces a brief monophasic fever typical of LP. Further, human monocytes release LP when incubated with TSS filtrates in vitro. The monocyte products also stimulate the proliferation of mouse thymocytes in the presence of phytohemagglutinin in a manner characteristic of LAF. A bacterial filtrate is much less effective without an intermediate incubation with monocytes. The stimulation of monocyte IL-1 production is easily quantified, provides a simple method of assaying the TSS toxin, and since it involves human cells, is directly relevant to the human disease. The assay was used to monitor the purification of TSS toxin. Only 0.1 ng/ml of the purified material is required to induce monocyte IL-1 production. It is thus more potent than endotoxin. In contrast to endotoxin, its effect is not blocked by polymyxin B. We conclude that in TSS the sudden fever and probably other components of the acute phase response may be attributed to a massive release of IL-1.

Thymocyte activating factor(s) in human gingival fluids

Human gingival fluid contains a low-molecular-weight factor (10,000 to 25,000) which enhances the proliferation of murine thymocytes in the presence of suboptimal doses of mitogen. Although the gingival fluid has no Interleukin 2 (T cell growth factor) activity, as indicated by its inability to induce proliferation of an IL 2 dependent lymphocytic cell line, it is directly mitogenic for dermal fibroblasts. These studies suggest that the thymocyte and fibroblast growth-promoting properties of human gingival fluid may have important functions in regulating inflammatory responses in the human periodontal tissues.

Effect of ultraviolet radiation on production of epidermal cell thymocyte-activating factor/interleukin 1 in vivo and in vitro

UV radiation was found to enhance the release by keratinocytes of epidermal cell thymocyte-activating factor (ETAF), a hormone-like molecule that is physiochemically identical to interleukin 1 (IL-1). This conclusion was supported by the following observations: (i) the keratinocyte cell line PAM 212 retained ETAF/IL-1-producing potential after exposure to UV radiation despite significant loss in cell viability; (ii) epidermal cells from normal and UV radiation-exposed mice were found to produce equivalent amounts of ETAF/IL-1 on a per cell basis with the density of epidermal cells in UV radiation-exposed skin being at least 5-fold above normal values; (iii) under the conditions used, ETAF/IL-1 could be detected in the serum of UV radiation-exposed, but not normal, animals; and (iv) many of the biologic consequences known to be mediated by elevations in ETAF/IL-1--i.e., neutrophilia, elevated levels of complement component 3, serum amyloid P, and plasma fibrinogen--were all observed in animals following a single UV radiation exposure. Animals subjected to chronic UV radiation showed an initial elevation in their levels of acute-phase reactants that returned to normal concentrations within 7 days. This correlates with observations made by others of a "desensitization" to ETAF/IL-1-mediated effects after chronic administration of known exogenous stimulators of inflammatory responses. Further, the UV radiation-induced desensitization took place in spite of demonstrable serum levels of ETAF/IL-1. These results suggest that the mechanism(s) responsible for desensitization is not an inhibition of ETAF/IL-1 synthesis but rather may result from inability of the target cells to perceive this endogenous mediator or to unavailability of serum-associated ETAF/IL-1 for the appropriate targets.