A sensitive, IL-2-independent, assay for IL-1

Inflammasome activators induce interleukin-1α secretion via distinct pathways with differential requirement for the protease function of caspase-1

Through their capacity to sense danger signals and to generate active interleukin-1β (IL-1β), inflammasomes occupy a central role in the inflammatory response. In contrast to IL-1β, little is known about how IL-1α is regulated. We found that all inflammasome activators also induced the secretion of IL-1α, leading to the cosecretion of both IL-1 cytokines. Depending on the type of inflammasome activator, release of IL-1α was inflammasome dependent or independent. Calcium influx induced by the opening of cation channels was sufficient for the inflammasome-independent IL-1α secretion. In both cases, IL-1α was released primarily in a processed form, resulting from intracellular cleavage by calpain-like proteases. Inflammasome-caspase-1-dependent release of IL-1α and IL-1β was independent of caspase-1 catalytic activity, defining a mode of action for caspase-1. Because inflammasomes contribute to the pathology of numerous chronic inflammatory diseases such as gout and diabetes, IL-1α antagonists may be beneficial in the treatment of these disorders.

Granzyme A is an interleukin 1 beta-converting enzyme

Apoptosis is critically dependent on the presence of the ced-3 gene in Caenorhabditis elegans, which encodes a protein homologous to the mammalian interleukin (IL)-1 beta-converting enzyme (ICE). Overexpression of ICE or ced-3 promotes apoptosis. Cytotoxic T lymphocyte-mediated rapid apoptosis is induced by the proteases granzyme A and B. ICE and granzyme B share the rare substrate site of aspartic acid, after which amino acid cleavage of precursor IL-1 beta (pIL-1 beta) occurs. Here we show that granzyme A, but not granzyme B, converts pIL-1 beta to its 17-kD mature form. Major cleavage occurs at Arg120, four amino acids downstream of the authentic processing site, Asp116. IL-1 beta generated by granzyme A is biologically active. When pIL-1 beta processing is monitored in lipopolysaccharide-activated macrophage target cells attacked by cytotoxic T lymphocytes, intracellular conversion precedes lysis. Prior granzyme inactivation blocks this processing. We conclude that the apoptosis-inducing granzyme A and ICE share at least one downstream target substrate, i.e., pIL-1 beta. This suggests that lymphocytes, by means of their own converting enzyme, could initiate a local inflammatory response independent of the presence of ICE.

Quantification of recombinant human interleukin-1 alpha by a specific two cell immunobioassay

The detection of picogram quantities of recombinant human IL-1 alpha in human and rat serum was accomplished by a sensitive and specific two cell immunobioassay. The specificity is provided by an IL-1 alpha specific mouse IgM monoclonal antibody which is non-neutralizing thus allowing for the addition of the EL-4 NOB-1 cell line directly to the IL-1 alpha monoclonal antibody complex. The above cell line is then converted to an IL-2 producer line in response to the captured IL-1 alpha. Supernatant from the EL-4 NOB-1 cells is then added to the IL-2 dependent CTLL-2 line and cell proliferation measured by thymidine incorporation. This assay has the advantage of specificity provided by the antibody capture step, sensitivity provided by the EL-4 NOB-1 line (1-50 pg/ml) and finally ease of maintenance of the responder cell line which requires no feeder cells or mitogens. Data are reported on the sensitivity, precision, reproducibility and specificity of the assay, the stability of rhIL-1 alpha in serum and the recovery of rhIL-1 alpha from serum. We also report on the use of this procedure to assay samples from rats given ascending doses of rhIL-1 alpha.

Suppression of cell-mediated immunity by street rabies virus infection

An attempt to define a severe suppression of cell-mediated immunity by street rabies virus infection was undertaken by using the mice lethally and peripherally infected with a street rabies virus (1088 strain). The cell-mediated cytotoxic (CMC) activity of the spleen cells from those mice once slightly increased until day 4 after infection but declined rapidly thereafter until their death on days 10 to 12 after infection. In parallel with a decrease of CMC response of the spleen cells from 1088-infected mice, proliferative response to Con A, IL-2 activity in the culture supernatants of Con A-induced proliferation, responsiveness to exogenously added IL-2 and to Con A to express IL-2R, of those cells became suppressed, and the marked decrease of the total number of spleen cells was observed. Selective depletion of CD4+ and CD8+ cells in the spleens, abnormalities of IL-1 and E-type prostaglandins (PGE2) production or production of inhibitory component able to block IL-2 activity by spleen cells were not observed and these factors did not appear to be associated with the suppression of proliferative response to Con A. However, an apparent association of CD8+ cells in the suppression of differentiation of pre-cytotoxic lymphocytes (CTL) into CTL was demonstrated in the co-culture experiments of the spleen cells from 1088-infected mice with spleen cells of mice infected with an attenuated rabies virus (ERA strain) which can induce higher levels of CMC response. There was no evidence of the productive replication of rabies virus in thymus and spleen of 1088-infected mice. The relationship of these observations to current theories on virus-induced immunosuppression was discussed.

Cloning, expression and characterization of ovine interleukins 1 alpha and beta

Ovine interleukin 1 alpha (IL-1 alpha) c-DNA, obtained by polymerase chain reaction, has been cloned into pTZ18R and pTZ19R. The resulting DNA sequence shows close homology with the bovine sequence. The derived amino-acid sequence shows conserved motifs similar to those observed in all species studied so far. No signal peptide is seen. Northern blots of RNA from lipopolysaccharide (LPS)-stimulated ovine alveolar macrophages show IL-1 beta m-RNA to be produced earlier than and to be more transient than IL-1 alpha m-RNA. c-DNAs coding for the IL-1 alpha proprotein and IL-1 alpha and IL-1 beta mature proteins have been cloned and expressed in the yeast Ty-VLP system as fusion proteins. The resultant IL-1 protein preparations, cleaved from their fusion partners by the action of activated coagulation Factor Xa, are 80-95% pure and show biological activity in standard thymocyte co-mitogen and cartilage degradation assays for IL-1. Some species specificity is observed in that sheep thymocytes are more responsive to ovine rIL-1 than are mouse thymocytes. The presence of a Factor Xa cleavage site in the IL-1 alpha proprotein suggests that Factor Xa may be involved in the processing of ovine IL-1 alpha to its mature form.

Regional and cellular codistribution of interleukin 1 beta and nerve growth factor mRNA in the adult rat brain: possible relationship to the regulation of nerve growth factor synthesis

We have found a regional distribution of IL 1 beta mRNA and IL 1 activity in the normal adult rat brain, which reveals at least partially a colocalization with nerve growth factor (NGF). The predominantly neuronal signal patterns were found over the granule cells of the dentate gyrus, the pyramidal cells of the hippocampus, the granule cells of the cerebellum, the granule and periglomerular cells of the olfactory bulb, and over dispersed cells of the ventromedial hypothalamus and of the frontal cortex. In these areas also the highest levels of IL 1 activity were observed. In the striatum and septum much lower levels of IL 1 beta mRNA and IL 1 activity (shown for the striatum), most likely synthesized by glial cells, could be determined. IL 1 beta-expressing cells were mainly found in brain regions that also synthesize NGF mRNA as shown by in situ hybridization. NGF mRNA could be demonstrated over pyramidal cells of the hippocampus, granule cells of the dentate gyrus, periglomerular cells of the olfactory bulb and over prefrontal cortex neurons. These data indicate that IL 1 beta, among other factors, might also play a regulatory role in the synthesis of NGF in the CNS, as has been demonstrated in the peripheral nervous system (Lindholm, D., R. Heumann, M. Meyer, and H. Thoenen. 1987. Nature (Lond.). 330:658-659).

Lymphocytic choriomeningitis virus-induced immunodepression: inherent defect of B and T lymphocytes

Infection of mice with lymphocytic choriomeningitis virus (LCMV) produces a rapidly induced immuno-suppression manifested by low lymphocyte proliferation in response to lipopolysaccharide (LPS) and concanavalin A (ConA). Analysis of the mechanisms underlying the unresponsiveness to these mitogens was undertaken at the cellular and molecular levels 7 days after infection. The selective elimination of CD8+ T cells and the results of coculture experiments demonstrated that unresponsiveness was not due to suppressor cells. Similarly, the role of inhibitory factors such as prostaglandins was excluded, since indomethacin, which inhibits their production, did not reverse the unresponsiveness. Analysis of different cytokines secreted by ConA-activated macrophages or T cells revealed that interleukin-1 (IL-1), synthesized during the T-dependent activation of macrophages by ConA, was normally produced by cells from LCMV-infected mice. In contrast, IL-2, which is produced by activated CD4+ T cells, was undetectable. Addition of exogenous IL-2 did not restore the proliferative response, although the p55-kilodalton protein of the IL-2 receptor was induced by ConA on CD4+ cells from LCMV-infected mice. Our results can be interpreted as showing that (i) unresponsiveness to mitogens of cells from LCMV-infected mice is not due to altered functions of the macrophages with respect to IL-1 production; (ii) CD4+ cells are activated, since the p55 chain of the IL-2 receptor is induced; (iii) the lack of IL-2 production cannot explain T-cell unresponsiveness, since addition of exogenous IL-2 did not restore the proliferative response. Taken together, these data suggest that T-lymphocyte unresponsiveness should be related to an inherent proliferative defect subsequent to T-cell activation and IL-2 receptor expression.

Cytokine regulation of human monocyte interleukin-1 (IL-1) production in vitro. Enhancement of IL-1 production by interferon (IFN) gamma, tumour necrosis factor-alpha, IL-2 and IL-1, and inhibition by IFN-alpha

IL-1 production (secreted and cell-associated) was measured in monocyte cultures stimulated by a variety of agents in vitro. Monocytes either adherent to conventional plastic culture plates in serum-free conditions, or in suspension in culture medium containing serum were stimulated to produce IL-1 during culture. In non-adherent, serum-free conditions, monocytes produced very low or undetectable amounts of IL-1 during 20 h of culture. Lipopolysaccharide (LPS) induced equivalent amounts of secreted and cell-associated IL-1, although at very low concentrations more cell-associated IL-1 was produced. IL-1 production in response to LPS could be augmented by crude lymphokine, IFN-gamma, or tumour necrosis factor (TNF) alpha. TNF-alpha preferentially augmented the production of cell-associated IL-1 in LPS-stimulated cultures. TNF-alpha induced a significant amount of IL-1 (mainly cell-associated) directly but could also induce IL-1 secretion when combined with IL-2 or IFN-gamma, or when in the presence of serum. IL-2 acted synergistically with low concentrations of IFN-gamma or IL-1 to induce significant levels of IL-1 production. IFN-alpha did not induce any IL-1 production, but was a potent inhibitor of IL-1 production induced by a variety of stimuli. These results suggest that IL-1 production may be enhanced or reduced by different cytokines at concentrations likely to be found in chronic inflammatory lesions.

A sensitive IL-1 thymocyte co-stimulator assay using a novel beta-D-galactoside specific lectin from the beetle, Allomyrina dichotoma

A sensitive thymocyte co-stimulator assay of IL-1 using a beta-D-galactoside specific lectin (allo A) obtained from the beetle (Allomyrina dichotoma) is reported here. Allo A stimulated [3H]thymidine uptake of mouse thymocytes in the presence of IL-1. The allo A assay was more sensitive than the PHA or PNA- thymocyte assay, especially at low doses of IL-1. Optimal conditions for the allo A assay were as follows: allo A, 2.5-5.0 micrograms/ml; whole thymocytes, 0.5-1.0 x 10(6) cells/well; incubation time, 72-96 hr. The assay is sensitive and convenient and can easily be performed in any laboratory.

Brain neocortex modulation of mitogen-induced interleukin 2, but not interleukin 1, production

Interleukin 2 (IL-2) production by splenic T cells stimulated by Concanavalin A was studied in mice after unilateral or bilateral brain neocortex ablation. The brain cortex was shown to modulate IL-2 production in an asymmetrical way. IL-2 levels were higher in animals with a right cortical lesion (group R) and lower in mice with a symmetrical lesion (group L) as compared to controls, differences between groups R and L being significant. Such variations of IL-2 production that were observed after unilateral lesions were abolished with bilateral cortical ablations. These results extend the immunoregulatory roles of the brain neocortex to IL-2 production by splenic T cells and may provide molecular support for neuro-immunological networks.

Comparison of phorbol-12-myristate-13-acetate and dioctanoyl-sn-glycerol in the activation of EL4/6.1 thymoma cells

The present study compared the role of two protein kinase C (PK-C) activating agents, the phorbol ester phorbol-12-acetate-13-myristate (PMA) and the membrane-permeating diacylglycerol dioctanoyl-sn-glycerol (DiC8) in the activation of EL4/6.1 thymoma cells. These cells have been shown to express interleukin-2 receptors (IL-2R) upon stimulation with optimal amounts of PMA (10 ng/ml); also, suboptimal amounts of PMA (1 ng/ml) synergized with the Ca2+ ionophore ionomycin and recombinant interleukin-1 (rIL-1) (Lowenthal et al., 1986). Comparing PMA and DiC8 led to the following results: PMA at 10 ng/ml induced IL-2R; in contrast, DiC8 (30-3 micrograms/ml) alone was unable to induce IL-2R, although it did synergize with ionomycin (0.5 micrograms/ml) and rIL-1. Bihourly additions of DiC8 did not change this pattern. The addition of DiC8 together with rIL-2 also resulted in no IL-2R expression. Furthermore, DiC8 (10 micrograms/ml) effectively translocated PK-C. Therefore, the differences observed between PMA and DiC8 do not seem to be due to differences in metabolism or to an inability to translocate PK-C. Analysis of messenger (m) RNA produced in stimulated EL4/6.1 cells revealed that DiC8 was also unable to induce mRNA for IL-2R. Our data suggest that PMA, especially at "optimal" concentrations, might have effects that cannot be mimicked by diacylglycerol. Furthermore, it seems that the deficient activity of diacylglycerols can be compensated for by a Ca2+ ionophore and, depending on the cellular system, by further signals such as IL-1.

Interleukin-1 in adrenal chromaffin cells

Interleukin-1, first identified as a macrophage factor of importance in infections and inflammation, is a protein with properties of an endogenous pyrogene and lymphocyte activating factor. Occurrence of interleukin-1-like immunoreactivity was demonstrated in the noradrenergic chromaffin cells of the rat and mouse adrenal gland by means of two antisera raised against synthetic peptides corresponding to the amino acid sequences 169-194 and 201-215 of the murine interleukin-1 precursor protein. These antisera also inhibited stimulation of interleukin-2 receptor expression by purified human interleukin-1. Reserpine, which is known to deplete catecholamines, also caused release of the interleukin-1-like immunoreactive material. The interleukin-1 content of the rat adrenal medulla was estimated by radioimmunoassay, and if released the adrenal interleukin-1 pool may result in plasma interleukin-1 levels of about 10(-12). The interleukin-1-immunoreactive material obtained from the rat adrenal gland was characterized as a trypsin-sensitive protein with a molecular weight in the range of 13,000-19,000. This protein fraction stimulated interleukin-2 receptor expression on human T-cells as earlier shown for interleukin-1.

Urtica dioica agglutinin, a new mitogen for murine T lymphocytes: unaltered interleukin-1 production but late interleukin 2-mediated proliferation

Urtica dioica agglutinin, a small-molecular-weight lectin purified from stinging nettle rhizomes, induces murine cell proliferation. U. dioica agglutinin is a specific T-cell mitogen for both thymocytes and spleen T lymphocytes; its mitogenic properties are strictly dependent on the presence of accessory cells. The kinetics of proliferation are markedly different from those of the classical T-cell mitogen concanavalin A, with a 2 to 3-day delay for both splenic and thymic populations and a rate of DNA synthesis twofold lower than that observed with concanavalin A. The late T-lymphocyte proliferation induced by U. dioica agglutinin correlates well with (i) the observed late interleukin-2 production and interleukin-2 receptor expression, and (ii) the long-lasting cyclosporin A-sensitive early activation period. In contrast, the production of interleukin-1 is not different, both in terms of concentration and kinetics, from that observed with concanavalin A.