Seed germination, seedling emergence, seed persistence and triflusulfuron-methyl sensitivity in Galinsoga parviflora and G. quadriradiata

Galinsoga quadriradiota Ruiz and Pavon (hairy galinsoga) and Galinsogo parviflora Cav. (smaliflower galinsoga, gallant soldier) are very troublesome weeds in many vegetable row crops in Europe. In order to optimize further management strategies for Galinsoga control in-depth study of germination biology was performed. Germination experiments were conducted to evaluate the impact of light and alternating temperatures on germination of a large set of Galinsoga populations. Seedling emergence was investigated by burying seeds at different depths in a sand and sandy loam soil. Dormancy of fresh achenes harvested in autumn was evaluated by studying germination response in light at 25/20 degrees C with and without nitrate addition. Seed longevity was investigated in an accelerated ageing experiment by exposing seeds to 45 degrees C and 100% relative humidity. A dose-response pot experiment was conducted in the greenhouse to evaluate the effectiveness of triflusulfuron-methyl, applied at the one leaf pair stage, for controlling Belgian Galinsoga populations. Galinsoga seeds required light for germination; light dependency varied among populations. Seedling emergence decreased drastically with increasing burial depth. Maximum depth of emergence varied between 4 and 10mm depending on soil type and population. In a sandy soil, emergence percentages were higher and seedlings were able to emerge from greater depths than in a sandy loam soil. Freshly produced G. parviflora seeds showed a varying but high degree of primary dormancy and were less persistent than G. quadriradiata seeds which lack primary dormancy. Galinsoga parviflora populations were more sensitive to triflusulfuron-methyl than G. quadriradiata populations. The lack of primary dormancy, high seed persistence and lower herbicide sensitivity may explain the higher distribution and abundance of G. quadriradiata over G. parviflora populations in Belgium. Overall, features such as lack of primary dormancy of freshly harvested G. quadriradiata seeds and light dependency for germination may be used to optimize and develop Galinsoga management strategies.

(E)-2(R)-[1(S)-(Hydroxycarbamoyl)-4-phenyl-3-butenyl]-2'-isobutyl-2'-(methanesulfonyl)-4-methylvalerohydrazide (Ro 32-7315), a selective and orally active inhibitor of tumor necrosis factor-alpha convertase

Tumor necrosis factor-alpha (TNF-alpha), a cytokine secreted by inflammatory cells, has been implicated in several inflammatory disease states. (E)-2(R)-[1(S)-(Hydroxycarbamoyl)-4-phenyl-3-butenyl]-2'-isobutyl-2'-(methanesulfonyl)-4-methylvalerohydrazide (Ro 32-7315), is a potent, orally active inhibitor of the TNF-alpha convertase (TACE), an enzyme responsible for proteolytic cleavage of the membrane bound precursor, pro-TNF-alpha. Ro 32-7315 inhibited a recombinant form of TACE (IC(50) = 5.2 nM) with selectivity over related matrix metalloproteinases. In a cellular assay system, THP-1 cell line, and in human and rat whole blood, Ro 32-7315 significantly reduced lipopolysaccharide (LPS)-induced TNF-alpha release with IC(50) values of 350 +/- 14 nM (n = 5), 2.4 +/- 0.5 microM (n = 5), and 110 +/- 18 nM (n = 5), respectively. Oral administration of Ro 32-7315 to Wistar rats caused a dose-dependent inhibition of LPS-induced release of systemic TNF-alpha with an ED(50) of 25 mg/kg. Treatment (days 0-14) of Allen and Hamburys hooded rats with Ro 32-7315 (2.5, 5, 10, and 20 mg/kg, i.p., twice daily) significantly reduced adjuvant-induced secondary paw swelling (42, 71, 83, and 93%, respectively) as compared with the vehicle group. In the Ro 32-7315-treated group, the reduced paw swelling was associated with improved lesion score and joint mobility. Furthermore, in a placebo-controlled, single-dose study, Ro 32-7315 given orally (450 mg) significantly suppressed ex vivo, LPS-induced TNF-alpha release in the whole-blood samples taken from healthy male and female volunteers (mean inhibition of 42% over a 4-h duration, n = 6). These data collectively support the potential use of such a compound for the oral treatment of inflammatory disorders.

Tumor angiogenesis induced by granulocyte chemotactic protein-2 as a countercurrent principle

Chemokine production by tumors is a well-known phenomenon, but its role in tumor biology remains debatable. Although intratumoral injection of granulocyte chemotactic protein-2 (GCP-2) had no effect on tumor parameters, needle-free stable expression of the chemokine resulted in enhanced tumor growth. It is shown here that tumors that express a potent form of GCP-2 induce a strong influx and activation of tumor-associated neutrophils. The production of GCP-2 leads to intratumoral expression of gelatinase B and advantage for tumor growth by increased angiogenesis. These results are in line with the countercurrent principle of chemokine action and support the notion that paraneoplastic expression of ELR-positive CXC chemokines has to be blocked rather than stimulated in cancer therapy.

Efficient secretion of biologically active recombinant OB protein (leptin) in Escherichia coli, purification from the periplasm and characterization

The genes encoding the mature forms of mouse (mOB) and human OB (hOB) protein (also called leptin) were fused to the secretion signal coding sequence of the Escherichia coli outer membrane protein A (sOMP A). The hybrid genes were preceded by a ribosome binding site (RBS) and were expressed under transcriptional control of both the lipoprotein promoter (Plpp) and the lac promoter-operator (POlac). The recombinant fusion proteins were efficiently expressed and exported into the periplasmic compartment of E. coli cells from where they were recovered by osmotic shock as soluble mature polypeptides with the sOMP A precisely removed. Recombinant mOB and hOB proteins were also produced in Sf9 insect cells using the baculovirus expression system. Milligram quantities of both proteins were purified to homogeneity using ion-exchange, hydrophobic interaction chromatography and gel filtration and were found to be biologically active and to have antiobesity effects upon testing in genetically obese ob/ob mice.

Ligand-independent dimerization of the extracellular domain of the leptin receptor and determination of the stoichiometry of leptin binding

The leptin receptor is a class I transmembrane protein with either a short or a long cytoplasmic domain. Using chemical cross-linking we have analyzed the binding of leptin to its receptor. Cross-linking of radiolabeled leptin to different isoforms of the leptin receptor expressed on COS-1 cells reveals leptin receptor monomer, homodimer, and oligomer complexes. Cotransfection of the long and short form of the leptin receptor did not provide any evidence for the formation of heterodimer complexes. Soluble forms consisting of either the entire extracellular domain or the two cytokine receptor homologous domains of the leptin receptor were purified to homogeneity from recombinant baculovirus-infected insect cells by leptin affinity chromatography. Gel filtration chromatography showed that these proteins exist in a dimeric form. Analysis of the complex formed between soluble leptin receptor and leptin by native polyacrylamide gel electrophoresis, and data obtained from the amino acid composition of the complex provide direct evidence that the extracellular domain of the leptin receptor binds leptin in a 1:1 ratio.

A human leptin mutant induces weight gain in normal mice

Leptin, a fat secreted hormone, regulates ingestive behaviour and energy balance by binding to a specific receptor. Using site-directed mutagenesis, we screened for single amino acid residues in human leptin which are critical for receptor binding and biological activity. Here we report that one of these mutants has in vivo antagonistic properties. An Arg to Gln substitution at position 128 of human leptin does not affect receptor binding but knocks out biological activity. Repeated injection of R128Q in normal C57BL/6J mice results in a progressive increase in body weight. This demonstrates that R128Q is able to interfere with the negative feedback control of endogenous leptin. This mutant could be of therapeutic use for wasting disorders, such as anorexia and cachexia, where weight gain would be beneficial.

Leptin receptor (OB-R) signaling. Cytoplasmic domain mutational analysis and evidence for receptor homo-oligomerization

The leptin receptor (OB-R) mediates the weight regulatory effects of the adipocyte secreted hormone leptin (OB). Previously we have shown that the long form of OB-R, expressed predominantly in the hypothalamus, can mediate ligand-induced activation of signal transducer and activator of transcription factors 1, 3, and 5 and stimulate transcription via interleukin-6 and hematopoietin receptor responsive gene elements. Here we report that deletion and tyrosine substitution mutagenesis of OB-R identifies two distinct regions of the intracellular domain important for signaling. In addition, granulocyte-colony stimulatory factor receptor/OB-R and OB-R/granulocyte-colony stimulatory factor receptor chimeras are signaling competent and provide evidence that aggregation of two OB-R intracellular domains is sufficient for ligand-induced receptor activation. However, signaling by full-length OB-R appears to be relatively resistant to dominant negative repression by signaling-incompetent OB-R, suggesting that mechanisms exist to permit signaling by the long form of OB-R even in the presence [corrected] of excess naturally occurring short form of OB-R.

ESM-1 is a novel human endothelial cell-specific molecule expressed in lung and regulated by cytokines

We here report the identification of a novel human endothelial cell-specific molecule (called ESM-1) cloned from a human umbilical vein endothelial cell (HUVEC) cDNA library. Constitutive ESM-1 gene expression (as demonstrated by Northern blot and reverse transcription-polymerase chain reaction analysis) was found in HUVECs but not in the other human cell lines tested. The cDNA sequence contains an open reading frame of 552 nucleotides and a 1398-nucleotide 3'-untranslated region including several domains involved in mRNA instability and five putative polyadenylation consensus sequences. The deduced 184-amino acid sequence defines a cysteine-rich protein with a functional NH2-terminal hydrophobic signal sequence. Searches in several data bases confirmed the unique identity of this sequence. A rabbit immune serum raised against the 14-kDa COOH-terminal peptide of ESM-1 immunoprecipitated a 20-kDa protein only in ESM-1-transfected COS cells. Immunoblotting and immunoprecipitation of HUVEC lysates revealed a specific 20-kDa band corresponding to ESM-1. In addition, constitutive ESM-1 gene expression was shown to be tissue-restricted to the human lung. Southern blot analysis suggests that a single gene encodes ESM-1. A time-dependent up-regulation of ESM-1 mRNA was seen after addition of tumor necrosis factor alpha (TNFalpha) or interleukin (IL)-1beta but not with IL-4 or interferon gamma (IFNgamma) alone. In addition, when IFNgamma was combined with TNFalpha, IFNgamma inhibited the TNFalpha-induced increase of ESM-1 mRNA level. These data suggest that ESM-1 may have potent implications in the areas of vascular cell biology and human lung physiology.

OB protein binds specifically to the choroid plexus of mice and rats

Binding studies were conducted to identify the anatomical location of brain target sites for OB protein, the ob gene product. 125I-labeled recombinant mouse OB protein or alkaline phosphatase-OB fusion proteins were used for in vitro and in vivo binding studies. Coronal brain sections or fresh tissue from lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats were probed to identify potential central OB protein-binding sites. We report here that recombinant OB protein binds specifically to the choroid plexus. The binding of OB protein (either radiolabeled or the alkaline phosphatase-OB fusion protein) and its displacement by unlabeled OB protein was similar in lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats. These findings suggest that OB protein binds with high affinity to a specific receptor in the choroid plexus. After binding to the choroid plexus receptor, OB protein may then be transported across the blood-brain barrier into the cerebrospinal fluid. Alternatively, binding of OB protein to a specific receptor in the choroid plexus may activate afferent neural inputs to the neural network that regulates feeding behavior and energy balance or may result in the clearance or degradation of OB protein. The identification of the choroid plexus as a brain binding site for OB protein will provide the basis for the construction of expression libraries and facilitate the rapid cloning of the choroid plexus OB receptor.

Identification and expression cloning of a leptin receptor, OB-R

The ob gene product, leptin, is an important circulating signal for the regulation of body weight. To identify high affinity leptin-binding sites, we generated a series of leptin-alkaline phosphatase (AP) fusion proteins as well as [125I]leptin. After a binding survey of cell lines and tissues, we identified leptin-binding sites in the mouse choroid plexus. A cDNA expression library was prepared from mouse choroid plexus and screened with a leptin-AP fusion protein to identify a leptin receptor (OB-R). OB-R is a single membrane-spanning receptor most related to the gp130 signal-transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. OB-R mRNA is expressed not only in choroid plexus, but also in several other tissues, including hypothalamus. Genetic mapping of the gene encoding OB-R shows that it is within the 5.1 cM interval of mouse chromosome 4 that contains the db locus.

Recombinant mouse OB protein: evidence for a peripheral signal linking adiposity and central neural networks

The recent positional cloning of the mouse ob gene and its human homology has provided the basis to investigate the potential role of the ob gene product in body weight regulation. A biologically active form of recombinant mouse OB protein was overexpressed and purified to near homogeneity from a bacterial expression system. Peripheral and central administration of microgram doses of OB protein reduced food intake and body weight of ob/ob and diet-induced obese mice but not in db/db obese mice. The behavioral effects after brain administration suggest that OB protein can act directly on neuronal networks that control feeding and energy balance.

Detailed analysis of the IL-5-IL-5R alpha interaction: characterization of crucial residues on the ligand and the receptor

The receptor for interleukin-5 (IL-5) is composed of two different subunits. The IL-5 receptor alpha (IL-5R alpha) is required for ligand-specific binding while association with the beta-chain results in increased binding affinity. Murine IL-5 (mIL-5) has similar activity on human and murine cells, whereas human IL-5 (hIL-5) has marginal activity on murine cells. We found that the combined substitution of K84 and N108 on hIL-5 by their respective murine counterpart yields a molecule which is as potent as mIL-5 for growth stimulation of a murine cell line. Since the unidirectional species specificity is due only to the interaction with the IL-5R alpha subunit, we have used chimeric IL-5R alpha molecules to define regions of hIL-5R alpha involved in species-specific hIL-5 ligand binding. We found that this property is largely determined by the NH2-terminal module of hIL-5R alpha, and detailed analysis defined D56 and to a lesser extent E58 as important for binding. Moreover, two additional residues, D55 and Y57, were identified by alanine scanning mutagenesis within the same region. Based on the observed homology between the NH2-terminal module and the membrane proximal (WSXWS-containing) module of hIL-5R alpha we located this stretch of four amino acid residues (D55, D56, Y57 and E58) in the loop region that connects the C and D beta-strands on the proposed tertiary structure of the NH2-terminal module.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of critical residues in the cytoplasmic domain of the human interleukin-5 receptor alpha chain required for growth signal transduction

Interleukin (IL)-5 binds to a cell surface receptor composed of two polypeptide chains, alpha and beta, both belonging to the hemopoietic cytokine receptor family. Mouse cells expressing common mouse beta chain (AIC2B) that were transfected with human IL-5 receptor (R)alpha cDNA proliferated in response to picomolar concentrations of human IL-5, indicating that a functional receptor was reconstituted. We show that in these cells, human (h)IL-5 as well as mouse (m)IL-3 induce tyrosine phosphorylation of beta chain and JAK 2 kinase. Phosphorylated beta receptor was co-precipitated with anti-JAK 2 antibodies, suggesting that both molecules were physically associated. IL-5 and IL-3 also induce cytosolic DNA binding activity as measured by an electrophoretic mobility shift assay using the interferon-gamma responsive region of human Fc gamma 1 gene DNA element. A deletion mutant of hIL-5R alpha lacking the cytoplasmic part could bind hIL-5 normally in association with the beta chain, but was unable to transmit a biological signal. The cytoplasmic domain was also indispensable for tyrosine phosphorylation and activation of DNA binding proteins. A membrane-proximal proline-rich element of the hIL-5R alpha cytoplasmic domain that is conserved among different members of the hemopoietic cytokine receptor family was essential for biological activity. Point mutations in this motif also knocked out IL-5-inducible JAK 2 phosphorylation.

Interleukin-5 and its receptor: a drug target for eosinophilia associated with chronic allergic disease

A characteristic feature of chronic allergic diseases such as asthma is the increase in eosinophil numbers in the inflamed tissue. In light of its specificity for the development of eosinophils, interleukin-5 (IL-5) is considered the most important cytokine involved in the regulation of eosinophilia. Hence, an antagonist for IL-5 activity is a new target for drug discovery programs. We have examined the opportunity for both a random and a rational approach for the identification of such an antagonist. The elucidation of the structure of IL-5 and the initial structure/function analysis of the ligand/receptor complex constitute a first step towards the design of antagonistic compounds. The identification of a small compound by random screening able to inhibit the IL-5/IL-5 receptor interaction indicated an important domain in the receptor. We examine here protein-based IL-5 antagonists, such as IL-5-muteins, soluble IL-5 receptor constructs, and monoclonal antibodies, for their potential as IL-5/IL-5 receptor antagonists, and the use of a murine model of eosinophil airway inflammation for their evaluation.

Identification of receptor-binding domains on human interleukin 5 and design of an interleukin 5-derived receptor antagonist

A detailed structure-function analysis of human interleukin 5 (hIL5) has been performed. The hIL5 receptor is composed of two different polypeptide chains, the alpha and beta subunits. The alpha subunit alone is sufficient for ligand binding, but association with the beta subunit leads to a 2- to 3-fold increase in binding affinity. The beta chain is shared with the receptors for IL3 and granulocyte/macrophage-colony-stimulating factor--hence the descriptor beta C (C for common). All hIL5 mutants were analyzed in a solid-phase binding assay for hIL5R alpha interaction and in a proliferation assay using IL5-dependent cell lines for receptor-complex activation. Most residues affecting binding to the receptor alpha subunit were clustered in a loop connecting beta-strand 1 and helix B (mutants H38A, K39A, and H41A), in beta-strand 2 (E89A and R91A; weaker effect for E90A) and close to the C terminus (T109A, E110A, W111S, and I112A). Mutations at one position, E13 (Glu13), caused a reduced activation of the hIL5 receptor complex. In the case of E13Q, only 0.05% bioactivity was detected on a hIL5-responsive subclone of the mouse promyelocytic cell line FDC-P1. Moreover, on hIL5-responsive TF1 cells, the same mutant was completely inactive and proved to have antagonistic properties. Interactions of this mutant with both receptor subunits were nevertheless indistinguishable from those of nonmutated hIL5 by crosslinking and Scatchard plot analysis of transfected COS-1 cells.

Structure/function analysis of human interleukin 5 and its receptor

We have performed a detailed structure-function analysis of human interleukin 5 (hIL5) and its receptor. By testing a hIL5 mutant panel in a solid phase binding assay and a proliferation assay using hIL5 dependent cell-lines, areas on hIL5 involved in either the receptor alpha-subunit interaction or in receptor activation were identified. Epitope mapping data of a neutralizing and a non-neutralizing monoclonal antibody were in agreement with the mutant analysis. hIL5 binding areas on the IL5R alpha-subunit were identified by interspecies chimaera analysis. Finally, hIL5 mutants with reduced receptor activation potential have antagonistic properties.

Covalent modification of the interleukin-5 receptor by isothiazolones leads to inhibition of the binding of interleukin-5

Using a fusion protein of the human interleukin-5-receptor alpha chain (hIL5R alpha) and the human IgG C gamma 3 chain (hIL5R alpha-h gamma 3), we have developed a solid-phase assay for high-flux screening of a collection of synthetic compounds. We report on the identification of isothiazolone derivatives as potent inhibitors of binding of interleukin-5 (IL5) to the hIL5R alpha, as measured in a solid-phase assay (soluble hIL5R alpha or hIL5R alpha-h gamma 3) or on COS-1 cells expressing the hIL5R alpha on the cell membrane. The binding of hIL4 and human granulocyte macrophage colony-stimulating factor (hGM-CSF) to their respective receptors is not inhibited by the isothiazolones in similar assay systems. Scatchard analysis revealed that these compounds caused a decrease in affinity of the IL5R alpha for IL5. The inhibition of binding IL5 to its receptor by the isothiazolone derivatives is abrogated by free-sulfhydryl-containing compounds such as dithiothreitol, indicating that the isothiazolones react with the sulfhydryl group of free cysteine residues in the hIL5R alpha. Mutation of Cys66 led to a receptor which still binds hIL5, but which was insensitive to the inhibition by isothiazolones. Mutation of Cys249 and Cys296 to serine resulted in complete loss of IL-5-binding activity. The use of radio-labeled isothiazolone confirmed that Cys66, present in the first domain of the receptor, is the target for covalent modification leading to a decrease in affinity.

B7/CD28-dependent IL-5 production by human resting T cells is inhibited by IL-10

We analyzed the effects of rIL-10 on IL-5 production by human resting T cells isolated from peripheral blood. Resting T cells of healthy individuals required activation for 48 h with either anti-CD3 mAb cross-linked on B7/CD32-transfected mouse fibroblasts or PMA in conjunction with anti-CD28 mAb for optimal IL-5 secretion. In each condition, IL-5 secretion measured by ELISA was inhibited in a dose-dependent manner by rIL-10, whereas IFN-gamma production was not suppressed. The inhibitory effect of rIL-10 on IL-5 synthesis induced by PMA and anti-CD28 mAb was also observed at the mRNA level. In contrast with its action on T cells costimulated by B7/CD28 signaling, rIL-10 did not block IL-5 secretion in response to PMA and A23187 calcium ionophore. The inhibition of IL-5 production by rIL-10 was not due to IL-2 deprivation because it was not modified by the addition of exogenous rIL-2. Moreover, cyclosporin A, which inhibited IL-2 more efficiently than rIL-10 in response to anti-CD3 mAb and B7/CD32 transfected fibroblasts, did not reduce and even enhanced IL-5 production. Finally, we analyzed the influence of endogenously produced IL-10 on IL-5 secretion by T cells stimulated by PMA and anti-CD28 mAb. Addition of a neutralizing anti-IL-10 mAb increased IL-5 release in this system, indicating that endogenous IL-10 controls IL-5 production. We conclude that both rIL-10 and endogenous IL-10 inhibit IL-5 production by T cells costimulated by B7/CD28 signaling.

B7/CD28-dependent IL-5 production by human resting T cells is inhibited by IL-10

We analyzed the effects of rIL-10 on IL-5 production by human resting T cells isolated from peripheral blood. Resting T cells of healthy individuals required activation for 48 h with either anti-CD3 mAb cross-linked on B7/CD32-transfected mouse fibroblasts or PMA in conjunction with anti-CD28 mAb for optimal IL-5 secretion. In each condition, IL-5 secretion measured by ELISA was inhibited in a dose-dependent manner by rIL-10, whereas IFN-gamma production was not suppressed. The inhibitory effect of rIL-10 on IL-5 synthesis induced by PMA and anti-CD28 mAb was also observed at the mRNA level. In contrast with its action on T cells costimulated by B7/CD28 signaling, rIL-10 did not block IL-5 secretion in response to PMA and A23187 calcium ionophore. The inhibition of IL-5 production by rIL-10 was not due to IL-2 deprivation because it was not modified by the addition of exogenous rIL-2. Moreover, cyclosporin A, which inhibited IL-2 more efficiently than rIL-10 in response to anti-CD3 mAb and B7/CD32 transfected fibroblasts, did not reduce and even enhanced IL-5 production. Finally, we analyzed the influence of endogenously produced IL-10 on IL-5 secretion by T cells stimulated by PMA and anti-CD28 mAb. Addition of a neutralizing anti-IL-10 mAb increased IL-5 release in this system, indicating that endogenous IL-10 controls IL-5 production. We conclude that both rIL-10 and endogenous IL-10 inhibit IL-5 production by T cells costimulated by B7/CD28 signaling.

IL-5 in post-traumatic eosinophilic pleural effusion

Thoracic trauma or pneumothorax can result in pleural fluid eosinophilia. In this study we investigated the role of the eosinophilopoietic cytokine IL-5 in three cases of post-traumatic eosinophilic pleural effusions (EPE). Using a specific immunoenzymatic assay, significant levels of IL-5 were found in EPE (range 100-3000 pg/ml), while IL-5 was undetectable (< 25 pg/ml) in corresponding serum samples and in non-eosinophilic pleural fluids. IL-5 present in pleural fluids was found bioactive in a proliferative assay using a mouse CTLL-2 cell line transfected with the cDNA corresponding to the alpha chain of the human IL-5 receptor. Using a reverse polymerase chain reaction (PCR) method, we found IL-5 mRNA expression within pleural mononuclear cells from patients with EPE, but not in corresponding peripheral blood mononuclear cells (PBMC), confirming that IL-5 is synthesized locally in the pleural cavity. In the two cases in which pleural CD4+ cells were purified, these cells were identified as the major source of IL-5. Taken together, these data indicate that the development of post-traumatic EPE is related to a local secretion of IL-5 by CD4+ cells present in the pleural cavity.

Recombinant soluble human interleukin-5 (hIL-5) receptor molecules. Cross-linking and stoichiometry of binding to IL-5

Recombinant soluble human interleukin-5 receptor alpha (shIL-5R alpha) has been expressed in COS-1 cells and in baculovirus-infected cells. The protein was purified from the supernatant by chromatography on concanavalin A-Sepharose, MonoQ, and a final gel filtration step. A chimeric fusion receptor protein (hIL-5R alpha-h gamma 3) was constructed by fusion of the cDNA corresponding to the shIL-5R alpha to the cDNA corresponding to the Fc part of the human IgG C gamma 3 chain, and was expressed in baculovirus-infected insect cells. The chimeric receptor was secreted as a disulfide-linked homodimer, and was purified by protein G affinity chromatography. In a solid-phase binding assay the shIL-5R alpha and the bivalent hIL-5R alpha-h gamma 3 were found to bind hIL-5 with a similar affinity, corresponding to the membrane-bound, low affinity hIL-5R alpha. SDS-polyacrylamide gel electrophoresis of shIL-5R alpha cross-linked to radiolabeled hIL-5, suggested that one shIL-5R alpha molecule binds to one hIL-5 homodimer molecule. Gel filtration studies of the complex formed between the shIL-5R alpha and hIL-5 pointed toward the same stoichiometry of binding. The formation of such a complex could be observed by electrophoresis in native gels. Immunoaffinity chromatography using a non-neutralizing monoclonal antibody directed against hIL-5, followed by size column chromatography, allowed the purification of the complex. The data obtained from the amino acid analysis of the constituents of the complex blotted from an SDS-polyacrylamide gel, and from the amino acid composition of the complex blotted from a native polyacrylamide gel, provided direct evidence that the shIL-5R alpha binds the hIL-5 dimer in a 1:1 ratio.

Organization and chromosomal localization of the human interleukin 5 receptor alpha-chain gene

The gene for the hIL-5R alpha subunit, which is present in a single copy in the human genome, has been analysed in detail. It is located on chromosome 3 in the region 3p26. The gene organization reflects its relationship to the cytokine/haematopoietin receptor superfamily. Three introns are located in the 5' untranslated region. The subsequent exons determine the functional domains of the hIL-5R alpha protein: the signal peptide, three fibronectin type III-like (FN-like) modules, each built up by two exons, the membrane anchor and two exons forming the cytoplasmic tail, the first of which contains the proline cluster region. In addition, a specific exon generating a soluble isoform is located before the membrane anchor exon. This specific exon contains an in frame TAA stop codon, followed by a polyadenylation signal. Hence, a normal splicing event leads to a soluble IL-5R alpha variant, whereas alternative splicing is required for cell membrane anchoring. A second area of alternative splicing is found in the 5' leader sequence, and possibly relates to the presence of short open reading frames preceding the main ATG. All intron-exon junctions meet the GT-AG rule. The gene structures of all cytokine/haematopoietin receptors documented so far have also been compared with respect to intron phasing. This shows that all introns between the FN-III-like modules are of the +1 type, but in addition, splice sites within the Cys-module and WS-WS-module are invariably of the +2 and 0 type, respectively.

Molecular basis of the membrane-anchored and two soluble isoforms of the human interleukin 5 receptor alpha subunit

By use of a 3' extension PCR strategy, cDNA clones were isolated spanning the transmembrane region and a complete cytoplasmic domain of the human interleukin 5 receptor alpha subunit (hIL5R alpha). These cDNAs differ from previously isolated clones encoding a soluble hIL5R alpha form by a sequence switch at position 1243. When expressed in COS-1 cells, only low-affinity binding of 125I-labeled human interleukin 5 was observed. Coexpression of the hIL5R beta chain led to a 2-fold increase in binding affinity. In addition, this same cloning strategy allowed us to identify a putative second soluble isoform of hIL5R alpha. Genomic data revealed that the two soluble variants arise from either a "normal" splicing event or from the absence of splicing, whereas synthesis of the membrane-anchored form requires alternative splicing.

Precursor frequency analysis of human cytolytic T lymphocytes directed against autologous melanoma cells

Limiting numbers of peripheral-blood mononuclear cells (PBMC) from melanoma patients were stimulated with irradiated autologous tumor cells in the presence of interleukins-2 and -4 and in the absence of feeder cells. The responder cells were restimulated every week. After 2 to 4 weeks, the microcultures were tested for their lytic activity against the autologous tumor cells. Significant lysis of the tumor cells was observed with a fraction of these microcultures, whereas no lysis was observed with control microcultures seeded without stimulator melanoma cells. Because our aim was to measure the precursor frequency of CTL showing specificity for the tumor, and not that of NK-like effectors that were also capable of lysing the melanoma cells, we used cold-target inhibition with an excess of NK target K562 to inhibit the NK-like activity. Microcultures whose lysis on the tumor cells was not abolished by K562 competition were observed. The specificity of these CTL clones was confirmed by the absence of lytic activity on autologous T-cell blasts. The numbers of microcultures with anti-tumor CTL activity fitted the zero-order of the Poisson distribution equation, indicating that they resulted from the activity of single T-cell clones. The frequency of anti-tumor CTL precursor cells (CTL-P) of 7 melanoma patients ranged from 1/900 to 1/33,000. Frequencies of anti-tumoral CTL-P were higher and NK-like effectors were less frequent when sorted CD8+ T lymphocytes were used as responder cells.

Characterization of the murine IL-5 receptor complex with the use of a panel of monoclonal antibodies. Relationship to the murine IL-3 receptor

To obtain mAb against the murine IL-5R (mIL-5R), Wistar rats were immunized with B13 cells, a murine Ly-1+ (CD5+) pre-B cell line which is dependent on IL-3 or IL-5 for its growth. A first group of six mAb could immunoprecipitate, from detergent-lysed B13 cells, a 60-kDa polypeptide (p60) corresponding to the recently cloned mIL-5R alpha-chain. A second group of three mAb was able to immunoprecipitate a protein doublet of 130 to 140 kDa (p130 and p140) corresponding to the previously characterized mIL-3R and mIL-3R-like polypeptide, respectively. One mAb (25C9) specifically bound the p130 polypeptide only. Here we show that: 1) mAb directed against the mIL-5R p60 component completely block IL-5 binding; 2) mAb recognizing the p130-p140 doublet interfere with both IL-3 and IL-5 binding; 3) mAb recognizing p130-p140 block the high affinity binding of IL-5 and hence the high affinity mIL-5R consists of the association of the p60 and p130 and/or p140 component; 4) one particular mAb, 25C9, which binds only to the p130 polypeptide, interferes with only IL-3 binding, and has no effect on the binding of IL-5. These results on binding were corroborated by a biologic assay based on the cytokine-dependent proliferation of B13 cells. The results presented here support a model for the mIL-5R consisting of the alpha-chain (p60) associated with the p140 (IL-3R-like), whereas the p130 (IL-3R) is not involved in the IL-5R complex.

Characterization of the murine IL-5 receptor complex with the use of a panel of monoclonal antibodies. Relationship to the murine IL-3 receptor

To obtain mAb against the murine IL-5R (mIL-5R), Wistar rats were immunized with B13 cells, a murine Ly-1+ (CD5+) pre-B cell line which is dependent on IL-3 or IL-5 for its growth. A first group of six mAb could immunoprecipitate, from detergent-lysed B13 cells, a 60-kDa polypeptide (p60) corresponding to the recently cloned mIL-5R alpha-chain. A second group of three mAb was able to immunoprecipitate a protein doublet of 130 to 140 kDa (p130 and p140) corresponding to the previously characterized mIL-3R and mIL-3R-like polypeptide, respectively. One mAb (25C9) specifically bound the p130 polypeptide only. Here we show that: 1) mAb directed against the mIL-5R p60 component completely block IL-5 binding; 2) mAb recognizing the p130-p140 doublet interfere with both IL-3 and IL-5 binding; 3) mAb recognizing p130-p140 block the high affinity binding of IL-5 and hence the high affinity mIL-5R consists of the association of the p60 and p130 and/or p140 component; 4) one particular mAb, 25C9, which binds only to the p130 polypeptide, interferes with only IL-3 binding, and has no effect on the binding of IL-5. These results on binding were corroborated by a biologic assay based on the cytokine-dependent proliferation of B13 cells. The results presented here support a model for the mIL-5R consisting of the alpha-chain (p60) associated with the p140 (IL-3R-like), whereas the p130 (IL-3R) is not involved in the IL-5R complex.

A human high affinity interleukin-5 receptor (IL5R) is composed of an IL5-specific alpha chain and a beta chain shared with the receptor for GM-CSF

cDNA clones encoding two receptor proteins involved in the binding of human interleukin 5 (hIL5) have been isolated. A first class codes for an IL5-specific chain (hIL5R alpha). The major transcript of this receptor gene, as analyzed in both HL-60 eosinophilic cells and eosinophilic myelocytes grown from cord blood, encodes a secreted form of this receptor. This soluble hIL5R alpha has antagonistic properties. A second component of the hIL5R is found to be identical to the beta chain of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) high affinity receptor. The finding that IL5 and GM-CSF share a receptor subunit provides a molecular basis for the observation that these cytokines can partially interfere with each other's binding and have highly overlapping biological activities on eosinophils.

Molecular basis of a high affinity murine interleukin-5 receptor

The mouse interleukin-5 receptor (mIL-5R) consists of two components one of which, the mIL-5R alpha-chain, binds mIL-5 with low affinity. Recently we demonstrated that monoclonal antibodies (Mabs) recognizing the second mIL-5R beta-chain, immunoprecipitate a p130-140 protein doublet which corresponds to the mIL-3R and the mIL-3R-like protein, the latter chain for which so far no ligand has been identified. In this study we show that a high affinity mIL-5R can be reconstituted on COS1 cells by co-expression of the mIL-5R alpha-chain with the mIL-3R-like protein (beta-chain). Cross-linking of 125I-labeled mIL-5 to the COS1 cells co-transfected with both cDNAs revealed the same pattern as in B13 cells, i.e. two proteins of 60 and 130 kd which correspond to the low affinity mIL-5R alpha-chain and the mIL-3R-like protein, respectively. The dissociation rate of mIL-5 from this reconstituted high affinity site was lower than that of the low affinity site, whereas the association rate was unchanged. Nonetheless, the apparent dissociation constant (Kd) for this reconstituted receptor was still 10-fold higher than the Kd observed for B13 cells. Although the mIL-3R is greater than 90% homologous to the mIL-3R-like protein, no increase in affinity for mIL-5 was detected on COS1 cells co-transfected with the cDNAs for the mIL-5R alpha-chain and the mIL-3R protein.

Amino acid sequence analysis of a mouse interleukin 5 receptor protein reveals homology with a mouse interleukin 3 receptor protein

A polypeptide chain for the mouse interleukin 5 receptor (IL5R) was purified from detergent-lysed B13 cells, a mouse IL5-dependent pre-B cell line. Purification was by a single immunoaffinity chromatographic step using an anti-mouse IL5R monoclonal antibody, R52. Internal amino acid sequence was obtained from four trypsin-generated peptides. All peptides were found to be present in the published amino acid sequence of a mouse IL3R and the mouse IL3R-like protein deduced from the cDNA. This indicates that the mouse IL5R and the mouse IL3R have a homologous polypeptide in common and suggests that the specificity of these lymphokine receptors is mainly generated by association with another ligand-specific polypeptide chain.

Expression of the murine interleukin-5 receptor on Xenopus laevis oocytes

In this study we describe the use of Xenopus laevis oocytes for the detection of mRNA coding for a murine interleukin-5 (mI15) receptor. When injected with sucrose gradient fractionated polyA+ RNA derived from the murine 115-dependent pre B cell line B13, these oocytes could specifically bind 35S-methionine labeled mI15. A size of approximately 4000 nucleotides (25S) was estimated for the mRNA corresponding to the mIL5-binding activity. This binding was not blocked by a monoclonal antibody R52 specific for the MI15-receptor, suggesting that the oocytes express a different form of this receptor.

Characterization of interleukin 5 receptors on eosinophilic sublines from human promyelocytic leukemia (HL-60) cells

The T cell product interleukin 5 (IL-5) has been shown to be a key factor in the development and the maturation of the eosinophilic cell lineage. We report here on the detection of human IL-5 receptors on eosinophilic sublines of the promyelocytic leukemia HL-60. Sodium butyrate, which initiates differentiation to mature eosinophils, also induces the appearance of high affinity (Kd 1-5 X 10(-11) M) IL-5 binding sites on these cells. The receptors are specific for IL-5, since binding of radiolabeled ligand can only be inhibited with homologous or murine IL-5 and not by other cytokines. We further show that the receptors are functional, since IL-5 can stimulate the proliferation of these cells. Affinity crosslinking of surface-bound 125I human IL-5 or 35S mouse IL-5 identified two membrane polypeptides of approximately 60 and approximately 130 kD to which IL-5 is closely associated. The presence of granulocyte/macrophage-colony-stimulating factor or tumor necrosis factor during butyrate induction decreased the expression of IL-5 binding sites compared with control cultures. The identification and characterization of human IL-5 receptors on HL-60 sublines should provide new insight into the role of this cytokine in eosinophil differentiation.

Restrictive dermopathy with distinct morphological abnormalities

A newborn child is described with the fetal hypokinesia sequence as a consequence of a restrictive dermopathy. Remarkable findings in this infant were neonatal teeth and survival till age 4 months. Ultrastructural examination of the skin showed thin epidermis and absence of elastic fibres.

Expression of human and murine interleukin-5 in eukaryotic systems

A cDNA coding for murine interleukin-5 (IL-5) was isolated from the EL4.ExC5 cell line. With the exception of a single amino acid substitution at position 79 (Arg----His), it is identical to a published sequence. The coding sequence for human IL-5 was synthesized chemically, allowing the introduction of strategically located restriction enzyme cleavage sites. Both cDNAs were expressed in various eukaryotic systems. Deletion of the 3' untranslated region of the murine IL-5 gene led to a 5- to 10-fold increase in expression in Xenopus laevis oocytes and in NIH-3T3 cells. The highest production, however, was obtained in Sf9 cells using a baculovirus vector. Human IL-5 was obtained from transformed Saccharomyces cerevisiae as a secreted, mature form using an in-frame fusion to the leader sequence of alpha-mating type factor, and was purified to homogeneity. In all cases mentioned, IL-5 was found to be glycosylated, and its biological activity was dependent on a 40- to 50-kD homodimer configuration, linked together by disulfide bridges. Deglycosylation did not affect the biological activity. Recombinant human IL-5 is biologically active on some human B-CLL cells (proliferation in the presence of IL-2) and on murine BCl1 cells (proliferation) at a low specific activity (about 1-2 x 10(3) U/mg) and on human eosinophils (eosinophil peroxidase assay) at a high specific activity (at least 5 x 10(6) U/mg). Recombinant murine IL-5 from Sf9 cells has a specific activity of 1-2 x 10(7) U/mg in the BCl1 proliferation assay. An additive effect is seen in the presence of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) and a synergistic effect in the presence of murine IL-4.

Purification of human interleukin-4 produced in Escherichia coli

An interleukin-4 (IL4)-encoding cDNA isolated from human splenocytes was used to construct an expression plasmid that directs a high-level synthesis of mature IL4 protein in Escherichia coli. The expression was under the control of the major leftward promoter, pL, of phage lambda and the phage Mu ribosome-binding site. The IL4 protein was present as insoluble inclusion bodies in the bacterial extract. The IL4 could be solubilized in 5 M MgCl2 and was purified to homogeneity by several chromatographic steps. The yield of protein from bacteria ranged between 3 and 5 mg of IL4 protein per gram of wet cells. The specific activity of the recombinant human IL4 was about the same as that of the natural product.

Interleukin 1 alpha acts as an autocrine growth factor for RPMI 1788, an Epstein-Barr virus-transformed human B cell line

The Epstein-Barr virus-transformed B cell line RPMI 1788 constitutively produces autocrine growth factors with molecular masses of 17 kDa, 24 kDa and 35 kDa. All three molecular forms were completely neutralized with anti-interleukin (IL) 1 alpha antiserum. Although IL 1 alpha and IL 1 beta mRNA were both equally detectable by Northern blotting, no IL 1 beta activity was found in partially purified RPMI 1788 supernatant. The growth of low density-seeded RPMI 1788 cells is specifically dependent on the presence of either IL 1 alpha or IL 1 beta. Since no other cytokine was found to be capable of sustaining proliferation, this cell line is suitable for the identification and quantification of IL 1, even in the presence of other cytokines.

Slippage of DNA polymerase I during synthesis of ds-cDNA

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Production of stable cytolytic T-cell clones directed against autologous human melanoma

We have attempted to optimize the production of stable human cytolytic T lymphocyte clones directed against autologous melanoma cell lines. MLTC were restimulated every week with irradiated melanoma cells in medium containing human serum and IL-2. After 21 to 35 days, in 5 out of 6 patients, these cultures expressed a preferential cytolytic activity against the autologous melanoma cells, as compared to autologous EBV-B cells or NK target K562. Limiting dilution of MLTC responder cells was performed at times varying from days 7 to 28, in medium containing IL-2 and allogeneic EBV-B cells as feeders. Approximately 1% of these responder cells gave rise to CTL clones that lysed the autologous melanoma cells, but did not lyse K562 or autologous B cells. It was possible to maintain in culture for several months a large number of CTL clones that retained this specificity with high activity, and multiplied more than 5-fold every week. Some of these CTL clones were dependent on the presence of the autologous melanoma cells for their growth. With one melanoma, the use of autologous CTL clones made it possible to identify 3 different antigens on the tumor cells.

Structural studies of the carbohydrate chains of human gamma-interferon

Human gamma-interferon (IFN-gamma) was prepared biotechnologically using Chinese hamster ovary cells. These cells were shown to be able to produce glycosylated IFN-gamma. Sugar analysis revealed the presence of Man, Gal, GlcNAc, NeuAc and Fuc residues in a molar ratio of 3.8:2.0:3.5:0.6:0.4 suggesting the occurrence of N-glycosidically linked N-acetyllactosamine type of carbohydrate chains. For structure determination of these chains, the glycoprotein was subjected to the hydrazinolysis procedure, yielding oligosaccharide-alditols. The latter compounds were analysed by 500-MHz 1H-NMR spectroscopy. The carbohydrate material was found to consist of biantennary structures, exhibiting microheterogeneity as to the terminal sialic acids and the core Fuc residue: (Formula: see text). As similar carbohydrates are present on several human secreted proteins, this glycosyl group is not expected to be immunogenic in man. It remains to be established to what extent the carbohydrate chains of this biotechnologically produced IFN-gamma are identical to those of naturally occurring human IFN-gamma.

Cloning and structure of a mouse interleukin-2 chromosomal gene

Using non-stringent hybridization with a human interleukin-2 cDNA probe, we have isolated recombinant phages from a mouse genomic DNA library cloned in the EMBL3 phage. The sequence and organization of the mouse interleukin-2 (IL-2) gene was determined. By comparison with the human IL-2 sequence, three introns can be identified with lengths of 99, +/- 2 400, and +/- 1 900 base pairs, respectively. The mouse IL-2 gene codes for a polypeptide of 169 amino acids and contains a putative signal peptide of 20 amino acids. The homology to the human interleukin-2 is 72% at the nucleotide level in the coding part and 65% at the amino acid level. An extraordinary sequence, consisting of 12 consecutive CAG codons coding for glutamine, is found in the first exon.

Interferon-gamma modulates HLA class II antigen expression on cultured human thymic epithelial cells

Cultures of human thymic epithelial cells (TEC) were tested for the expression of HLA class I (A, B, C) and class II (DR and DC) antigens by indirect immunofluorescence. The epithelial nature of the cells was proven by using an antikeratin antiserum. A high level of expression (close to 100% positive cells) of HLA class I antigens was observed on TEC at the beginning of the culture and remained unchanged for up to 12 days. In contrast, HLA class II antigen expression (85% DR+ and 75% DC+ cells on day 2) decreased gradually and reached very low levels (less than 5% DR+ or DC+) by day 7 of culture. This loss of class II antigen expression was not seen when cultures were performed in the presence of supernatants from activated T cells containing interferon-gamma (IFN-gamma). Furthermore, the presence of recombinant IFN-gamma (rIFN-gamma) in the medium from the onset of culture maintained HLA-DR and DC antigen expression on a high number of cells (comparable to that observed on day 2 of culture). A large percentage of rIFN-gamma-treated cells also showed intracytoplasmic HLA-DR antigen expression. Addition of rIFN-gamma at various times after the onset of the culture led to a reinduction of DR and DC antigen expression. This effect of rIFN-gamma was observed in 48 hr with concentrations as low as 10 IU/ml and was apparently specific for this IFN species, in that rIFN-alpha was unable to modify HLA class II antigen expression at concentrations up to 1000 IU/ml. The increased expression of HLA class II antigen was truly due to induction in individual TEC, rather than selection of class II-positive cells, because induction under the influence of IFN-gamma was reversible and occurred in the absence of proliferation in mitomycin-treated or gamma-irradiated cultures. Our results indicate that synthesis and membrane expression of class II HLA antigens are enhanced by IFN-gamma in TEC cultures. This finding raises the possibility that IFN-gamma participates in the mechanisms that assure the permanent expression of DR and DC antigens observed in TEC in vivo, with potentially important functional consequences in terms of education for self recognition.

Interferon-gamma modulates HLA class II antigen expression on cultured human thymic epithelial cells

Cultures of human thymic epithelial cells (TEC) were tested for the expression of HLA class I (A, B, C) and class II (DR and DC) antigens by indirect immunofluorescence. The epithelial nature of the cells was proven by using an antikeratin antiserum. A high level of expression (close to 100% positive cells) of HLA class I antigens was observed on TEC at the beginning of the culture and remained unchanged for up to 12 days. In contrast, HLA class II antigen expression (85% DR+ and 75% DC+ cells on day 2) decreased gradually and reached very low levels (less than 5% DR+ or DC+) by day 7 of culture. This loss of class II antigen expression was not seen when cultures were performed in the presence of supernatants from activated T cells containing interferon-gamma (IFN-gamma). Furthermore, the presence of recombinant IFN-gamma (rIFN-gamma) in the medium from the onset of culture maintained HLA-DR and DC antigen expression on a high number of cells (comparable to that observed on day 2 of culture). A large percentage of rIFN-gamma-treated cells also showed intracytoplasmic HLA-DR antigen expression. Addition of rIFN-gamma at various times after the onset of the culture led to a reinduction of DR and DC antigen expression. This effect of rIFN-gamma was observed in 48 hr with concentrations as low as 10 IU/ml and was apparently specific for this IFN species, in that rIFN-alpha was unable to modify HLA class II antigen expression at concentrations up to 1000 IU/ml. The increased expression of HLA class II antigen was truly due to induction in individual TEC, rather than selection of class II-positive cells, because induction under the influence of IFN-gamma was reversible and occurred in the absence of proliferation in mitomycin-treated or gamma-irradiated cultures. Our results indicate that synthesis and membrane expression of class II HLA antigens are enhanced by IFN-gamma in TEC cultures. This finding raises the possibility that IFN-gamma participates in the mechanisms that assure the permanent expression of DR and DC antigens observed in TEC in vivo, with potentially important functional consequences in terms of education for self recognition.

Binding of unglycosylated and glycosylated human recombinant interferon-gamma to cellular receptors

Recombinant human interferons (IFNs), either unglycosylated produced in E. coli (rIFN-gamma) or glycosylated produced in CHO cells (g-rIFN-gamma), were labeled with 125I to similar specific activities to study their interaction with cell-surface receptors. When analyzed by gel electrophoresis, rIFN-gamma run as a single polypeptide of Mr 15,000-17,000, whereas g-rIFN-gamma separated into three components of Mr 20,000, 22,000, and 43,000, which corresponded to the known size of the two monomeric and one dimeric forms of glycosylated natural IFN-gamma. The binding of the two species of 125I-IFN-gamma was competed equally by rIFN-gamma in competition displacement experiments with Daudi cells, indicating that these IFNs bind with similar high affinity to the same receptors. KD values of 1.25 X 10(-10) and 2.5 X 10(-10) M were determined for g-rIFN-gamma and rIFN-gamma, respectively. This relatively small difference in KD does not apparently result in a detectable difference in biological activity, as measured by the increase in 2',5'-oligo(A) synthetase activity in IFN-treated HeLa and A549 cells. These results indicate that glycosylation of IFN-gamma does not play a significant role in its interaction with cellular receptors and in the induction of a biological response.

Recombinant interleukin 2 induces immunoglobulin secretion in Staphylococcus aureus Cowan strain I activated human B-cells

Human B-cells, exhaustively depleted for T-cells, were activated with Staphylococcus aureus Cowan strain I (SAC) and responded to recombinant human interleukin 2 (rIL2) by secretion of immunoglobulin (Ig), as measured by a protein A hemolytic plaque assay. The rIL2, however, had to be present early, since addition later than 24 h after SAC-activation of the B-cells reduced the response to background levels. No clear dose response was observed and Ig-secreting cells (ISC) could be induced even with rIL2 at 0.5 U/ml. The monoclonal antibody anti-TAC prevented the rIL2-promoted induction of ISC. Ig production could be induced in SAC-activated cultures with supernatants of Xenopus laevis oocytes injected with sucrose-gradient-fractionated poly(A+) RNA derived from a stimulated human spleen cell culture. This activity coincided with the IL2 mRNA activity and was well separated from the interferon-gamma mRNA activity. Our results suggest that IL2 is not only a B-cell growth factor but also promotes the differentiation of activated human B-cells towards Ig secretion.