Expression, purification, and refolding of recombinant fusion protein hIL-2/mGM-CSF

OBJECTIVE

To study the activities of interleukin (IL)-2 and granulocyte-macrophage colony-stimulating factor (GM-CSF) (hIL-2/mGM-CSF).

METHODS

SOE PCR was used to change the linker of the fusion protein for higher activities. The fusion protein was expressed in Escherichia coli (E. coli) BL21 (DE3) in inclusion body (IB) form. After IB was extracted and clarified, it was denatured and purified by affinity chromatography. The protein was refolded by dilution in a L-arginine refolding buffer and refined by anion chromatography. The protein activity was detected by cytokine-dependent cell proliferation assay.

RESULTS

The expression of hIL-2/mGM-CSF in E. coli yielded approximately 20 mg protein /L culture and the purity was about 90%. The specific activities of IL-2 and GM-CSF were 5.4 x 10(6) IU/mg and 7.1 x 10(6) IU/mg, respectively.

CONCLUSION

This research provides important information about the anti-tumor activity of hIL-2/mGM-CSF in vivo, thus facilitating future clinical research on hIL-2/mGM-CSF used in immune therapy.

Comparison of four methods for the purification and refolding of human interleukin-2-mouse granulocyte/macrophage colony-stimulating factor fusion protein

The combination of IL-2 (interleukin-2) and GM-CSF (granulocyte/macrophage colony-stimulating factor) has been broadly studied in antitumour immune therapy, but its efficacy is uncertain. To better exert the activities of the two cytokines and study them in a mouse model, we have constructed a bifunctional protein, hIL-2-mGM-CSF (human IL-2-mouse GM-CSF), fused to a C-terminal tag of six histidine residues (His(6)). The fusion protein was expressed in Escherichia coli as IBs (inclusion bodies). After extracting and clarifying the IBs, four methods of protein purification and refolding were compared in order to optimize the preparation technique. Of these methods, the best result was obtained with a four-step process consisting of (1) purification with denaturing affinity chromatography, (2) followed by fully denaturing the protein with system conversion, (3) then refolding by isovolumetric ultrafiltration and (4) finally, purification by anion-exchange chromatography. The purity of the hIL-2-mGM-CSF was approx. 95%, yielding approx. 20 mg of protein/l of culture. The fusion protein retained the natural activities of IL-2 and GM-CSF, with specific activities of 8.7 x 10(6) and 1.1 x 10(7) i.u./mg respectively. Flow-cytometric analysis indicated that hIL-2-mGM-CSF could specifically bind to the corresponding receptor-positive cells. The present study provides important preliminary information for studying the antitumour activity of hIL-2-mGM-CSF in vivo, which will facilitate future clinical research into the use of hIL-2/hGM-CSF in immune therapy.

Optimized conditions for high-level expression and purification of recombinant human interleukin-2 in E. coli

Interleukin-2 (IL-2), a potent cytokine has been used in anti-cancer therapy for over a decade now. IL-2, originally identified as a growth factor for T lymphocytes is a 15 kDa hydrophobic glycoprotein that induces the activation, clonal proliferation and differentiation of T and B-lymphocytes and enhances the cytotoxicity of monocytes and natural killer (NK) cells. Here, we report a simple method for the cloning, high-level expression and purification of IL-2 protein, which can be easily extended to other bioactive therapeutic proteins. The IL-2 gene was amplified from human spleen cDNA and cloned in a prokaryotic (E. coli) expression system. An optimal expression of the IL-2 protein was determined by varying the expression conditions like temperature, inducer concentration and duration of induction. The protein was expressed as inclusion bodies and a panel of reagents including detergents, urea and guanidine hydrochloride were used to solubilize it. After solubilization, the protein was renatured and subjected to a single step gel-filtration chromatography to yield immunobioactive IL-2 protein with > 99% purity.

A proteomic analysis of allograft rejection in rats after liver transplantation

In order to understand the allograft rejection in orthotopic liver transplantation (OLT), an allograft rejection rat model was established and studied by proteomic approach. The protein expression profiles of liver tissues were acquired by fluorescence two-dimensional difference gel electrophoresis (2D DIGE) that incorporated a pooled internal standard and reverse fluorescent labeling method. The expression levels of 27 protein spots showed significant changes in acute rejection rats. Among these spots, 19 were identified with peptide mass fingerprinting using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) after tryptic in-gel digestion. The results of the present paper could be helpful for our better understanding of allograft rejection in organ transplantation.

Comparison of RNA yield from small cell populations sorted by flow cytometry applying different isolation procedures

BACKGROUND

RNA from sorted cell populations is crucial in many instances. We therefore compared four current protocols for RNA isolation, with regard to mRNA yield and purity. Moreover, we examined the effects on RNA recovery caused by different storage reagents.

METHODS

Small populations of K562 cells or PMBC were sorted into the lysing reagent and subjected to RNA extraction, employing either phase separation extraction using an acidic guanidinium-isothiocyanate reagent (TriFast reagent), the silica-gel membrane-based spin-column technology (RNeasy Mini-/Micro-Kit), or the isolation via paramagnetic oligo(d)T-beads (microMACS). Cells designated for delayed RNA isolation were kept either in RNAlater, Qiagen Buffer RLT, TriFast or PrepProtect, or simply frozen after pelleting from PBS. The mRNA yield was determined by quantitative RT-PCR.

RESULTS

Performing unpaired two-tailed t-tests revealed that RNA was extracted in significantly higher amounts using magnetic bead isolation. This method also allowed best discrimination of induced IL2 gene expression. In contrast, phase separation extraction showed the highest rate of failures. Intermediate storage reduced RNA yield. Contamination by genomic DNA was detected in several samples subjected to phase separation or silica-gel membrane-based spin-column extraction.

CONCLUSIONS

Our results reveal advantages and disadvantages of RNA isolation procedures for small numbers of sorted cells and, therefore, facilitate the decision for the most appropriate protocol in a particular experimental context.

HIV-1 transgenic rat CD4+ T cells develop decreased CD28 responsiveness and suboptimal Lck tyrosine dephosphorylation following activation

Impaired CD4+ T cell responses, resulting in dysregulated T-helper 1 (Th1) effector and memory responses, are a common result of HIV-1 infection. These defects are often preceded by decreased expression and function of the alpha/beta T cell receptor (TCR)-CD3 complex and of co-stimulatory molecules including CD28, resulting in altered T cell proliferation, cytokine secretion and cell survival. We have previously shown that HIV Tg rats have defective development of T cell effector function and generation of specific effector/memory T cell subsets. Here we identify abnormalities in activated HIV-1 Tg rat CD4+ T cells that include decreased pY505 dephosphorylation of Lck (required for Lck activation), decreased CD28 function, reduced expression of the anti-apoptotic molecule Bcl-xL, decreased secretion of the mitogenic lympokine interleukin-2 (IL-2) and increased activation induced apoptosis. These events likely lead to defects in antigen-specific signaling and may help explain the disruption of Th1 responses and the generation of specific effector/memory subsets in transgenic CD4+ T cells.

In vivo CD4+ T-cell up-regulation and high dose side effects of refolded duck interleukin-2

The recombinant duck interleukin-2 (rduIL-2) monomer was firstly isolated under nature condition, and refolded by oxidization procedure. Refolded rduIL-2 monomer induced in vitro proliferation of Con A-stimulated duck splenocytes in a sensitive and dose-dependent manner, and up-regulated in vivo the amounts of CD4+ T cells with low dose of administration. However, high doses intermittent administration resulted in sever side effects in vivo, with typical lymphocytic interstitial pneumonitis and nephritis, and lymphocytic depletion in splenic corpuscle. Our findings might be beneficial to studies of both mechanism and applications in vivo of avian IL-2.

[Discovery of immature thymocyte proliferation factor]

An athymic mouse-derived immature T-cell clone, N-9F, was not maintained by interleukin-2 alone but required another soluble factor, contained in concanavalin A-stimulated rat splenocyte culture supernatant, namely T cell growth factor (TCGF), for its proliferation. An N-9F-proliferation factor (NPF) was isolated in a pure form from TCGF. N-9F cells and immature thymocytes proliferated in the presence of N-9F at 10(-12)-10(-9)M in a dose-dependent manner, but adult thymocytes were not stimulated by NPF. NPF increased DNA synthesis of N-9F. NPF increased CD4 and CD8 double negative, single positive and double positive thymocytes in fetal thymus organ culture. A hamster anti-NPF antiserum possessing the capacity to neutralize N-9F proliferation activity of NPF neutralized the increasing effect of NPF on immature thymocytes. All effects of NPF was inhibited by mAb QR6.6 to recognize a 100 kDa surface molecule of N-9F. The amino-terminal 20 amino acid sequence of NPF was identified and identical to that of rat saposin A. The apparent molecular weight of NPF, 16000, was comparable to that of saposin A. A Hitrap-mouse recombinant His-tag-saposin A antibody column bound NPF, pulled down the NPF activity in TCGF, and the antibody recognized a 16kDa molecule in western-blotting of TCGF. Thus, NPF in TCGF was a saposin A-like protein possessing the capacity for growth and differentiation of immature thymocytes. The physiological significance of NPF in the growth and differentiation of immature thymocytes was discussed in view of the characteristic distributions of NPF and the molecule recognized by its mAb QR6.6 in fetal thymi.

Expression and Purification of a Mutant of Human Interleukin-2 in Pichia pastoris

Interleukin (IL)-2 is a pharmacologically important cytokine secreted by T-lymphocytes. Recombinant IL-2 (rIL-2) has been modified and produced in many systems. Mass production of rIL-2 is the prerequisite for its wide application. Using a site-directed mutagenesis strategy, we first generated a gene coding for a new type of mutant of human IL-2 (MhIL-2), in which we replaced the cysteine-125 in human IL-2 with alanine, the leucine-18 with methionine, and the leucine-19 with serine. Then we investigated the possibility of its production of MhIL-2 in a Pichia pastoris system. High-level secreted expression of MhIL-2 was achieved by methanol induction. When purified with ultrafiltration, cation-exchange chromatography, and Sephadex G100 gel filtration, about 100 mg of MhIL-2 with high purity was obtained from 1 L of ferment supernatant. Biologic activity assay revealed that the purified recombinant protein displayed increased activity on proliferation of IL-2-dependent CTLL-2 cells. These results suggest that MhIL-2 is an improved IL-2 mutant that might hold great promise for clinical use, and that P. pastoris is an excellent system for the mass production of biologically active hIL-2.

Rapid purification of a new humanized single-chain Fv antibody/human interleukin-2 fusion protein reactive against HER2 receptor

Human embryonic kidney 293 cells were transfected with plasmid pcDNA-H520C9scFv-rhIL-2 containing a chimeric cDNA encoding the humanized 520C9 scFv/recombinant human IL-2 fusion protein (H520C9scFv-rhIL-2). The transfected cells in plateau growing phase were cultured in serum-free medium for three days. The supernatant was collected, concentrated and purified using an affinity column packed with CNBr-activated Sepharose 4B coupled with anti-rhIL-2 mouse monoclonal antibody. The purified fusion protein was analyzed by ELISA, SDS-PAGE and Western blot. The fusion protein showed only one band in both silver stained electrophoresis gel and Western blot developed by ECL chemiluminescence system. Its molecular weight was confirmed to be about 45 kD. This fusion protein possessed binding specificity against p185 positive SKOV3 and B16/neu cells, and it might stimulate IL-2-dependent CTLL-2 cell proliferation as well.

Construction of proteolysis resistant human interleukin-2 by fusion to its protective single chain antibody

Interleukin-2 (IL-2) is a 15 kDa cytokine secreted by T-cells. Consequence to its natural function as locally secreted short-term messenger, its half-life in circulation is short and provided mainly by fast renal clearance due to its low molecular weight and its proteolytic susceptibility. These are common characteristics for most cytokines, resulting in low clinical utility. In this study we report the construction of an IL-2 fusion-protein comprising a protective anti-hIL-2 single chain antibody that was selected from a phage display library and the hIL-2. This IL-2 fusion-protein is fully human and resistant to inactivation by the ubiquitous lysosomal protease-cathepsin D, which is implicated in the in vivo inactivation of IL-2. In contrast, the native IL-2 lost practically all of its activity under these conditions. This resistance is due to the interaction of the single chain domain with its epitope on IL-2 thus masking possible cleavage sites. We suggest that this 45 kDa proteolysis resistant IL-2 fusion-protein upon further increase of its molecular weight by common fusion techniques to at least 75 kDa will exhibit significantly longer half-life in vivo and a higher clinical utility than either the native IL-2 or any of its reported long T/2 derivatives.

Isolation and characterization of modified species of a mutated (Cys125 -Ala) recombinant human interleukin-2

During purification of recombinant and mutated interleukin-2 (rhIL-2A125) by reversed-phase-high-performance liquid chromatography, more and less hydrophobic fractions named MHF and LHF, respectively are discarded due to the presence of some unidentified forms of rhIL-2Ala125. Using slow and linear gradients of acetonitrile, these fractions were further purified by RP-HPLC, analyzed by automatic Edman degradation, digested with trypsin and analyzed by electrospray ionization mass spectrometry. In all fractions, partial processing of the N-terminal Met residue was observed. In the LHF the Met104 was partially oxidized as sulfoxide. Combining the selective and reversible blocking of tryptic peptides and cation-exchange chromatography, two unexpected C-terminal peptides were selectively isolated. Automatic N-terminal sequencing showed that one of these corresponded to the C-terminal peptide of rhIL-2Ala125 linked to another 11 amino acids (AANDENYALAA) and the other corresponded to the C-terminal peptide of a truncated rhIL-2Ala125 without the C-terminal threonine residue and the extension of the 11 amino acids previously mentioned. MHF contained a mixture of four species of rhIL-2A125 monoacetylated at the N-terminus and at the epsilon-amino groups of internal Lys residues: 8, 32 and 48. Cys58 was found as free cysteine and also covalently linked to Mr 69 and 77 molecules. Covalent dimers of rhIL-2A125 linked through disulfide bridges between Cys58 and Cys105 of different monomers were also found.

[Purification and renaturation of recombinant human interleukin-2-pseudomonas exotoxin (IL2-PE66(4GLU)) fusion protein]

OBJECTIVE

To evaluate the effect of a novel approach for purification and renaturation of recombinant human interleukin-2-pseudomonas exotoxin (IL2-PE66(4Glu)) fusion protein.

METHODS

A novel purification method established in our laboratory was adopted for the purification of the inclusion body, and after renaturation, recombinant human IL2-PE66(4Glu) fusion protein was purified by DEAE-Sepharose FF ion-exchange chromatography.

RESULTS

The purity of the fusion protein that retain its biological activity was as high as 95%, and a recovery rate over 80% of the refolded IL2-PE66(4Glu) fusion protein was achieved.

CONCLUSION

The purification and refolding method for inclusion body adopted in this study is simple and practical, which lays the foundation for a large-scale production of the fusion protein.

High-yield, in vitro protein expression using a continuous-exchange, coupled transcription/ translation system

The Rapid Translation System (RTS 500) (Roche Molecular Biochemicals) is a high-yield protein expression system that utilizes an enhanced E. coli lysate for an in vitro transcription/translation reaction. In contrast to conventional transcription/translation, this system allows protein expression to continue for more than 24 h. We demonstrated the utility of the RTS 500 by expressing different soluble and active proteins that generally pose problems in cell-based expression systems. We first expressed GFP-lunasin, a fusion protein that, because of its toxicity, has been impossible to produce in whole cells. The second protein we expressed, human interleukin-2 (IL-2), is generally difficult to produce, either as the native molecule or as a GSTfusion protein, in a soluble form in bacteria. Finally, we demonstrated the capacity of the RTS 500 to co-express proteins, by the simultaneous production of GFP and CAT in a single reaction. This new technology appears to be particularly usefulfor the convenient production of preparative amounts (100-900 microg) of proteins that are toxic or insoluble in cell-based systems.

Basic streptococcal superantigens (SPEX/SMEZ or SPEC) are responsible for the mitogenic activity of the so-called mitogenic factor (MF)

The mitogenic factor (MF) of group A streptococci has been reported to be a superantigen stimulating human T cells carrying Vbeta2, 4 and 8 and has been designated streptococcal pyrogenic exotoxin F (SPEF). MF was also shown to possess DNase activity. Here we have purified MF from culture supernatants of different Streptococcus pyogenes strains. Surprisingly, the MF preparations from different strains showed different Vbeta specificities depending on the expression of SPEC or SMEZ3 by the producing strain. Their mitogenic activity decreased upon further purification. In addition, the mitogenic activity could be only neutralized by antibodies against the basic streptococcal superantigens SPEC or SPEX (SMEZ3) but not by antibodies against MF itself although the latter were able to neutralize completely the DNase activity of MF. We found that streptodornase type B (SDB) was expressed in two molecular forms (SDBI and SDBII), differing only by one additional N-terminal arginine at SDBI. MF was found identical to the enzyme SDBII but is devoid of superantigenic properties and should no longer be called a superantigen or a pyrogenic exotoxin.

Cytokine expression and synovial pathology in the initiation and spontaneous resolution phases of adjuvant arthritis: interleukin-17 expression is upregulated in early disease

The aim of this study was to understand the immune processes controlling the initiation and spontaneous resolution of adjuvant arthritis (AA). We investigated synovial T-cell recruitment and mRNA expression of IL-17 and other important disease related cytokines, IFN-gamma, IL-2, IL-4, TNF and TGF-beta in inguinal lymph node (ILN) and synovial membrane (SM). Arthritis severity was assessed by a numerical rating score and rats were sacrificed every 3--4 days postadjuvant induction. Further assessment involved quantitative radiology and histology of the ankle joints on each day, and the ILN and SM were removed for RNA extraction. Cytokine mRNA expression was measured using RT-PCR and densitometry. Paraffin sections of rat ankle joints were stained for T-cells (CD3) by immunohistochemistry. In the ILN, there was an increase in IL-17, TNF and IFN-gamma expression in the early stages of disease, with a secondary sustained increase in IFN-gamma expression. In the SM, there was expression of T-cell cytokines in early arthritis (day 13), and prolonged TNF and TGF-beta expression, which reflected disease progression. IL-4 mRNA expression increased in the later stages of AA. Synovial T-cell numbers transiently increased at day 6, and remained high from days 13--28. Increased pro-inflammatory cytokine expression, including IL-17, in the ILN reflects the initiating events in the early stage of disease. IL-17 may therefore play an important role in the pathogenesis of AA. The increase in IL-4 (an anti-inflammatory cytokine) in the SM in the later stages of AA suggests that IL-4 is involved in the spontaneous resolution of AA. The initial increase in IFN-gamma in the ILN may reflect a pro-inflammatory response, while the prolonged secondary increase may indicate activation of regulatory T-cells.

Glucagon-induced self-association of recombinant proteins in Escherichia coli and affinity purification using a fragment of glucagon receptor

The specific molecular interactions of alpha-helical peptide, human glucagon (i.e., intermolecular self-association and specific receptor-binding affinity) provided a rationale for using the glucagon as the fusion expression partner to achieve high productivity of foreign proteins both in vivo (in bacterial fusion-expression system) and in vitro (in affinity column chromatography). The fusion of glucagon peptide(s) effectively promoted homogeneous aggregate formation of recombinant proteins while avoiding intermolecular crosslinking by disulfide bridges. High sensitivity of the self-aggregation to sequence effects resulted from two distinct nonpolar domains of glucagon, determining specificity of molecular interaction and aggregate size of recombinant proteins. An N-terminal domain of glucagon molecule (Phe6-Tyr10-Tyr13) could be a certain hydrophobic moiety involved in intermolecular self-association (probably, via helix-helix docking), while a C-terminal domain (Phe22-Trp25-Leu26) seems to critically affect the oligomer size in the off-pathway aggregation of synthesized fusion proteins. An N-terminal extracellular domain of human glucagon receptor was recombinantly expressed in Escherichia coli, immobilized to a chromatography column, and efficiently renatured to a conformation that attains high specificity in interaction with N-terminus glucagon molecules of recombinant fusion proteins. Through column chromatography employing the receptor fragment as affinity ligand, the recombinant proteins were efficiently purified from total intracellular proteins, and the long-term ligand stability was evidently proven through multiple cyclic-purification experiments. Major scaffolds for using protein ligands are large-scale production in a low-cost expression system and long-term stable operation with selective-binding affinity. From this point of view, the extracellular fragment of human glucagon receptor used in this study seems to be a new potent ligand for fusion protein-based affinity chromatography.

[Preliminary study on the purification of IL-2]

Interleukin-2 (IL-2) which is produced by T-lymphocytes is a protein molecule with the molecular weight of 15,420-Daltons. It has good functions in curing a lot of diseases such as cancer and AIDS even with a small quantity. A new method for purification of IL-2 by preparative high performance liquid chromatography is described. It was the first time to use hydroxyapatite as the packing to separate IL-2. IL-2 has one disulphide bridge (between 58th Cys and 105th Cys) and one free cysteine. In order to prevent aggregation and formation of wrong disulphide bond, 50 mumol/L Cu2+ and 1.5 mol/L guanidine hydrochloride was used for autoxidation and denaturing. Then we used mainly two chromatographic steps: First, Sephadex G-25 Gel permeation chromatography was used to separate guanidine hydrochloride and small molecules. Second, large scale preparative HPLC was used to separate impure protein from IL-2. Gradient elution was performed with phosphate buffer (pH 6.8). Its purity was examined by SDS-PAGE. Its activity reached 1 x 10(6) U/mg by CTLL-2 cell MTT method. The results showed that it is a suitable method for the large-scale purification of IL-2.

Antigen-dependent cytokine mRNA expression by individual rhesus macaque T helper cells by flow cytometry

Specific patterns of cytokine secretion by CD4(+) T helper (Th) cells determine the nature of immune effector responses. Using a multiparameter, flow cytometric fluorescent in situ hybridization (FISH) assay that detected cytoplasmic mRNA within intact cells, we assessed antigen-specific cytokine expression in rhesus macaque Th cells. In the peripheral lymphocytes of immunized rhesus macaques, FISH detected antigen-induced cytokine gene expression in single Th cells. Analysis of simultaneous cytokine expression by single cells demonstrated that the recall immune response consisted of Th cells expressing either a Th1 (IL-2(+)/IFN-gamma(+)) or a Th2 (IL-4(+)/IL-6(+)) cytokine pattern. In addition to the classic Th subsets, Th cells expressing only one of two Th1 or Th2 defining cytokines were common following antigen restimulation. The data gathered with the FISH assay suggest that, in primates, the immune response to recall antigens consists of nonclassic Th cells, as well as a mixture of polarized Th1 and Th2 T cells.

IL-2, its receptors, and bcl-2 and bax genes in normal, hyperplastic and carcinomatous human prostates: immunohistochemical comparative analysis

The presence of interleukin-2 (IL-2) and its receptors (Ralpha, Rbeta, Rgamma), and their relationship with the products of bcl-2 and bax genes was studied in normal prostates, benign prostatic hyperplasia (BPH), and prostatic cancer (PC) by ELISA, Western blot, and immunohistochemistry. A comparative semiquantitative immunohistochemical study was also performed. For all the antibodies assayed, immunoreactions were found in the epithelium and some stromal cells in the three types of specimens studied. These immunoreactions were much more higher in PC samples than in normal prostates. In BPH, immunoreactions were similar to that of normal prostates (bax), similar to that of PC (IL-2 and its three receptors), or intermediate between that of normal prostates and that of PC (bcl-2). Immunoexpressions of IL-2 and its receptors were found in the epithelial basal cells and some stromal cell of normal prostates and might be related to the control of the proliferation-apoptosis equilibrium. The increased expressions of IL-2 and its receptors in the epithelium of prostates in BPH, associated with increased bcl-2 expression which would account for the decrease in the apoptosis index that has been reported in this disorder. The increased expression of both bcl-2 and bax in PC might be involved in the higher apoptosis index reported in PC specimens. Since IL-2 administration seems to have an anti-tumour effect, the increased expression of this interleukin in BPH and PC could be interpreted as an attempt to hinder cell proliferation which would only be efficient at high doses.

[The application of liquid chromatography in genetic engineering]

The recent development of the molecular conformation, renaturation and intermediates on therapeutic proteins produced in biotechnology is reviewed. It also includs the quality control and in preparation of the therapeutic proteins in large scale by liquid chromatography in down-stream technology. This review includes 42 references.

RT-PCR amplification of various canine cytokines and so-called house-keeping genes in a species-specific macrophage cell line (DH82) and canine peripheral blood leukocytes

Total ribonucleic acid (RNA) isolated from a continuous canine macrophage cell line (DH82) was used in reverse transcription polymerase chain reactions (RT-PCR) for the detection of transcripts of interleukin (IL)-8, -12, and tumour necrosis factor-alpha (TNF). Three different methods of RNA isolation (standard guanidinium-thiocyanate method with and without application of RNA matrix, and boiling) were used and compared in regard to RT-PCR results. The most suitable method was used to establish RT-PCR amplification of mRNA transcripts of IL-2, -10, and interferon-gamma (IFN) in RNA isolated from canine peripheral blood leukocytes. Integrity of RNA isolates was ensured by amplification of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) or beta-actin, IL-8, -12, and TNF were amplified from RNA isolated by various methods. Use of guanidinium-thiocyanate with and without RNA matrix gave the most consistent results. Boiling as a mean of RNA isolation was quick and easy, but the RT-PCR results were extremely variable and multiple smaller bands were observed in the agarose gel in some preparations. IL-2, -10 and IFN transcripts were amplified from RNA isolated with guanidinium-thiocyanate from leukocytes stimulated with concanavalin A. DNase-treatment of RNA isolates was necessary to assure the destruction of genomic DNA and to avoid amplification of genomic sequences. This was especially a problem when using primers for GAPDH, beta-actin, IL-12, and TNF. Lack of DNase-treatment may lead to false positive results. This may be especially a problem when amplification of so-called house-keeping genes is used as internal control for RNA integrity. These findings demonstrated that isolation of total RNA with guanidinium-thiocyanate followed by DNase-treatment gave reliable and consistent results for detection of cytokine transcripts by RT-PCR in a canine macrophage cell line and canine peripheral blood leukocytes.

Expression and purification of human interleukin-2 simplified as a fusion with green fluorescent protein in suspended Sf-9 insect cells

A fusion protein of human interleukin-2 (hIL-2) and green fluorescent protein (GFP) was expressed in insect Sf-9 cells infected with recombinant baculovirus derived from the Autographa californica nuclear polyhedrosis virus (AcNPV). This fusion protein was comprised of a histidine affinity ligand for simplified purification using immobilized metal affinity chromatography (IMAC), UV-optimized GFP (GFPuv) as a marker, an enterokinase cleavage site for recovery of hIL-2 from the fusion, and the model product hIL-2. Successful production of hIL-2 as a fusion protein (approximately 52,000 Da) with GFPuv was obtained. GFPuv enabled rapid monitoring and quantification of the hIL-2 by simply checking the fluorescence, obviating the need for Western blot and/or ELISA assays during infection and production stages. There was no increased 'metabolic burden' due to the presence of GFPuv in the fusion product. The additional histidine residues at the N-terminus enabled efficient one-step purification of the fusion protein using IMAC. Additional advantages of GFP as a fusion marker were seen, particularly during separation and purification in that hIL-2 containing fractions were identified simply by illumination with UV light. Our results demonstrated that GFP was an effective non-invasive on-line marker for the expression and purification of heterologous protein in the suspended insect cell/baculovirus expression system.

Purification of human interleukin-2 fusion protein produced in insect larvae is facilitated by fusion with green fluorescent protein and metal affinity ligand

The fusion protein of green fluorescent protein (GFP) and human interleukin-2 (hIL-2) was produced in insect Trichoplusia ni larvae infected with recombinant baculovirus derived from the Autographa californica nuclear polyhedrosis virus (AcNPV). This fusion protein was composed of a metal ion binding site (His)6 for rapid one-step purification using immobilized metal affinity chromatography (IMAC), UV-optimized GFP (GFPuv), enterokinase cleavage site for recovering hIL-2 from purified fusion protein, and hIL-2 protein. The additional histidine residues on fusion protein enabled the efficient purification of fusion protein based on immobilized metal affinity chromatography. In addition to advantages of GFP as a fusion marker, GFP was able to be used as a selectable purification marker; we easily determined the correct purified fusion protein sample fraction by simply detecting GFP fluorescence.

High expression in bacteria and purification of polymorphic mouse interleukin 2 molecules

Recently, besides the known mouse interleukin 2 (IL-2) molecule, six other IL-2 alleles have been found in different mouse strains. In order to study their in vivo and in vitro biological activities large quantities are required. We cloned the corresponding IL-2 cDNAs into a pET7-7/BL21(DE3) bacterial system, a T7-RNA-polymerase-dependent expression vector, producing between 30 to 100 mg of IL-2 per litre of culture. The purification step is based on the resolution properties of the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) technique and the capability of the IL-2 to regain its activity after SDS denaturation. These purified IL-2 molecules supported the growth of an IL-2-dependent cell line, CTL-L2, in a similar way to a commercial mouse IL-2 control. However, RF IL-2 allele, which is also expressed in NOD mice had a relatively lower growth activity in the CTL-L2 assay. These IL-2 molecules can be obtained in a purified form and totally recovered their activity after elimination of the SDS and 2-mercaptoethanol used in the extraction procedure.

[New development of hydrophobic interaction chromatography and its applications in biochemical research]

This review is mainly concerned with the recent developments in (i) the retention mechanism of biopolymers in hydrophobic interaction chromatography (HIC); (ii) the synthesis of HIC packings, such as, the packings based on the inorganic and organic matrices, non-porous packings and porous membranes; (iii) the applications of HIC in both purifications of biopolymers and biochemical research, such as, renaturation and refolding of some denatured proteins, the change in molecular conformation of biopolymers. The review includes 62 references and a table.

Spontaneous expression of interleukin-2 in vivo in specific tissues of young mice

In situ hybridization and immunohistochemistry were used to determine the spectrum of tissues in which interleukin-2 (IL-2) mRNA and protein are found in healthy, normal young mice. In neonatal animals, IL-2 is expressed specifically by distinct, isolated cells at three major sites: the thymus, skin, and gut. Based on morphology and distribution, the IL-2-expressing cells resemble CD3epsilon+ T cells that are also present in all these locations. Within the thymus of postweanling animals, both TcRalphabeta and TcRgammadelta lineage cells secrete "haloes" of the cytokine that diffuse over many cell diameters. Within the skin, isolated cells expressing IL-2 are seen at birth in the mesenchyme, and large numbers of IL-2-expressing cells are localized around hair follicles in the epidermis in 3-week-old animals. At this age, a substantial subset of CD3epsilon+ cells is similarly localized in the skin. Significantly, by 5 weeks of age and later when the CD3epsilon+ cells are evenly distributed throughout the epidermis, IL-2 RNA and protein expression are no longer detectable. Finally, within the intestine, IL-2 protein is first detected in association with a few discrete, isolated cells at day 16 of gestation and the number of IL-2 reactive cells increases in frequency through E19 and remains abundant in adult life. In postnatal animals, the frequency of IL-2-positive cells in villi exceeds by greater than fivefold that found in mesenteric lymph node or Peyer's patches. Overall, these temporal and spatial patterns of expression provide insight into the regulation of IL-2 in vivo and suggest a role for IL-2 expression distinct from immunological responses to antigen.

Isolation of IL-2 receptor-beta cDNA clones from AtT-20 pituitary cells: constitutive expression and role in signal transduction

Interleukin-2 (IL-2) has been shown to stimulate ACTH secretion by anterior pituitary cells and has been implicated in pathophysiological processes of the pituitary and brain in several major neuropsychiatric disorders. The present study tested the hypothesis that IL-2 receptor-beta (IL-2R beta), a constitutively expressed and essential subunit for IL-2 signaling in lymphocytes, is expressed by AtT-20 pituitary cells and involved in transducing intracellular signals induced by IL-2. We isolated and sequenced three overlapping IL-2R beta cDNA clones from AtT-20 pituitary cells representing key regions of the gene protein coding sequence. These cDNA clones including conserved sequences shared by growth hormone and prolactin as well as intracytoplasmic Src and JAK family homology domains of nonreceptor protein tyrosine kinases essential for IL-2 signaling in lymphocytes. Their nucleotide sequences were 100% homologous with those expressed by lymphocytes (together they comprised 70% of the full length coding sequence). The IL-2R beta gene is constitutively expressed by AtT-20 pituitary cells, and its transcription was upregulated after CRF stimulation. Species-specific Il-2 induced intracellular signals in AtT-20 cells known to be mediated by Il-2R beta, including a transient increase in c-myc nuclear proto-oncogene transcription and the dose-dependent induction of DNA replication as measured by [3H]thymidine incorporation. The IL-2-induced DNA replication signal was not delivered by heat inactivated IL-2 and was partially blocked by a murine anti-IL-2R beta monoclonal antibody. These studies suggest that IL-2R beta may be a critical target involved in mediating the neuroimmunological actions of this prototypical cytokine in endocrine cells.

Comparative effects of bovine cytokines on cattle and bison peripheral blood mononuclear cell proliferation

Proliferation of peripheral blood mononuclear cells (PBMC) from cattle and bison was measured following stimulation of PBMC with bovine cytokines. Bovine interleukin 1 beta (BoIL-1 beta), interleukin 2 (BoIL-2) or granulocyte-macrophage colony-stimulating factor (BoGM-CSF) at 0.1-100 U/ml were incubated for 48 h with PBMC alone or with PBMC and various mitogens. These included concanavalin A (Con A), phytohemagglutinin (PHA), pokeweed mitogen (PWM) or Escherichia coli 055:B5 lipopolysaccharide (LPS) at 10-0.1 micrograms/ml. BoIL-2 alone, but not BoIL-1 beta and BoGM-CSF alone, induced proliferation of cattle and bison PBMC in the absence of mitogens. In addition, BoIL-1 beta and BoIL-2, but not BoGM-CSF, enhanced proliferation of cattle and bison PBMC induced by mitogens. These results indicate that BoIL-1 beta and BoIL-2 stimulate cattle and bison PBMC proliferation in a similar manner, whereas BoGM-CSF does not appear capable of stimulating either cattle or bison PBMC proliferation.

Construction and application of a prokaryotic vector which expresses the protein that can be quickly purified by IMAC

A vector was constructed by inserting a pair of complementary oligo nucleotides encoding 6 histidine residues into the polylinker's upstream of the prokaryotic high expression vector pBV220. The resultant vector is named pBV222. Proteins expressed by this vector will have a 6-histidine tail as an affinity handle fused to their N-terminus and can be quickly purified by one-step immobilized metal affinity chromatography (IMAC). This plasmid was verified by restriction mapping and DNA sequencing. When GM-CSF and IL-2 cDNA were closed into pBV222, expressed proteins in the inclusion body showed the predicted molecular weight and biological activity. The expressed bacteria were dissolved in 6 mol/L guanidine.HCl and the supernatant was loaded directly to IMAC. IL-2 and GM-CSF fusion proteins were eluted by the pH gradient, and over 90% purity was achieved.

Defective production of interleukin 2 in patients with Chagas' disease. Purified IL-2 augments in vitro response in patients with chagasic cardiomyopathy

The production of interleukin 2 (IL-2) by peripheral blood mononuclear cells, from patients with different clinical forms of Chagas' disease and healthy controls, was evaluated after stimulation with Trypanosoma cruzi antigen, PPD and PHA. PHA induced higher production of IL-2 in infected patients than healthy controls. No differences were found between infected groups. With PPD the trend was similar, the only difference was that asymptomatic infected patients (INF) showed higher levels of IL-2 production than patients with cardiomyopathy (CDM). With T. cruzi antigen, most patients showed little or no IL-2 production at 24 hr, a peak at 48 hr and an abrupt fall at 72 hr. A similar pattern of IL-2 production was observed in INF and CDM. To evaluate the physiologic relevance of the deficit in IL-2 production, we studied the effect of non-mitogenic concentrations of IL-2 in the proliferative response to specific antigens. The addition of IL-2 only enhanced the proliferative response of CDM patients. These observations suggest that patients suffering Chagas' disease, particularly CDM, have a significant reduction in the capacity to produce IL-2. These findings could be of importance in the pathogenesis of Chagas' disease.

The cloning, expression and purification of cervine interleukin 2

The cloning, sequencing and expression of cervine interleukin 2 (IL-2) is described. Cervine IL-2 cDNA is 489 base pairs long and shows high homology to bovine and ovine IL-2 (approximately 94%) with lower homologies to human (50%) and mouse (53%). The predicted protein sequence is 162 amino acids long with a signal sequence containing 20 amino acids. A molecular weight of 16273 Da was predicted for the mature protein. The expression plasmid pTRXFUS was redesigned to allow recombinant proteins to be expressed at high levels in a soluble form and subsequently affinity purified. This new plasmid, pTRXHIS, has been used to express the first cervine cytokine, IL-2. The fusion of the cervine IL-2 gene to the thioredoxin gene (TRX) stabilizes the recombinant product allowing the high expression of soluble IL-2. A polyHis (6 x Histidines) tag has been inserted between the two fusion partners which allows the fusion product to be affinity purified on a nickel-nitrilo-tri-acetic acid (Ni-NTA) column. The purified cervine IL-2 fusion protein was shown to be biologically active despite the presence of the TRX at the amino terminus. The TRX can be removed enzymatically with enterokinase releasing the biologically active IL-2 molecule. This expression system has several features that are useful in producing and purifying large quantities of biologically active cytokines.

Glutamine and tetrapeptide repeat variations affect the biological activity of different mouse interleukin-2 alleles

Mouse interleukin-2 (IL-2) was thought to be encoded by a single allele. We have recently described N-terminal differences in five IL-2 molecules from nine mouse strains analyzed (Matesanz, F., Alcina, A. and Pellicer, A., Immunogenetics 1993. 38: 300). In this study, we isolated and sequenced the cDNA of three polymorphic IL-2 molecules and constructed two recombinant IL-2 molecules to cover representative structural changes and to address the functional significance of these changes using human and mouse cellular assays in vitro. Apart from punctual codon changes, major differences include an expanding CAG codon (translated into glutamine) and the presence of the tetrapeptide Pro-Thr-Ser-Ser repeated 1, 2, or 3.5 times which is also present once in human IL-2. This tetrapeptide repeat includes an O-glycosylation site. These recombinant IL-2 proteins were expressed at high levels in bacteria and purified by preparative SDS-PAGE with a complete activity recovery. Differences in growth-inducing activity on mouse primary splenocytes were observed in some of them, although no differences were observed in proliferative stimulation of CTLL cells. In human peripheral blood lymphocytes and the T cell line Kit-225, the growth stimulation capacity was inversely dependent on the size of the glutamine stretch and the number of tetrapeptide repeats. These results suggest an evolutionary adaptation of the mouse IL-2/IL-2 receptor system that maintains polyglutamine extensions in the IL-2 molecule. In summary, mouse IL-2 polymorphism results in different bioactivities which may determine susceptibility or resistance to disease.

Covalent association of protein disulfide isomerase with recombinant human interleukin 2 in vitro

Protein disulfide isomerase has broad specificity in the catalysis of the formation and rearrangement of native disulfide bonds in proteins. This enzyme has two independent thioredoxin-like active sites (-CGHC-) and a peptide binding site. However, the mechanisms involving the catalytic processes are not clearly understood. It was reported that the enzyme associates with scrambled pancreatic ribonuclease A in vitro, and with misfolded human lysozyme in vivo. In the present study, recombinant human interleukin 2 has been chosen to probe the reaction intermediate in the reaction with the enzyme. We have identified and characterized a covalent associate formed in vitro by SDS-PAGE and Western blot analysis. This associate has a molecular weight of 71-72 kDa, the approximate sum of the molecular weights of the enzyme and the substrate. Western blot analysis confirmed that it formed via an intermolecular disulfide bond. Upon treatment with 2-mercaptoethanol, this bond was cleaved.

Expression of mammalian cytokines by Trypanosoma cruzi indicates unique signal sequence requirements and processing

A vector based upon the calmodulin-ubiquitin 2.65 locus of Trypanosoma cruzi has enabled the expression and secretion of the murine cytokines interleukin-2 (IL-2) and gamma-interferon (gamma-IFN) by transfected T. cruzi. The T. cruzi-derived cytokines were bioactive and produced by both epimastigotes and mammalian forms. The native coding sequence of IL-2 was sufficient to cause secretion of the protein, but the gamma-IFN signal sequence had to be replaced by the IL-2 signal sequence (IL-2/gamma-IFN) to allow efficient secretion of gamma-IFN. The amino acid sequences at the N-termini of the secreted T. cruzi-derived cytokines were different from the expected murine secreted protein. The secreted IL-2 was cleaved six amino acids downstream from the murine signal sequence cleavage site, and the hybrid IL-2/gamma-IFN molecule was cleaved three amino acids downstream from the predicted signal cleavage site in the IL-2/gamma-IFN molecule. These apparent differences in signal peptide sequence requirements and cleavage sites most likely indicate that the signal sequence processing in trypanosomes is distinct from that of higher eukaryotes.

Optimization of lyophilization conditions for recombinant human interleukin-2 by dried-state conformational analysis using Fourier-transform infrared spectroscopy

PURPOSE

Examination of the dried-state conformation of interleukin-2 (IL-2) was used to determine the pH conditions and stabilizers that provide optimal storage stability for the lyophilized product.

METHODS

Fourier-transform infrared spectroscopy and accelerated stability studies which examined solubility, aggregate formation, and covalent cross-linking were used.

RESULTS

Varying the pH in the absence of excipients resulted in dramatic differences in the dried state conformation of IL-2. At pH 7, IL-2 unfolds extensively upon lyophilization while at pH below 5 it remains essentially native. Additional unfolding was observed upon incubation at elevated temperatures. A strong direct correlation between the retention of the native (aqueous) structure during freeze-drying and enhanced stability is demonstrated. IL-2 prepared at pH 5 is approximately an order of magnitude more stable than at pH 7 with regard to formation of soluble and insoluble aggregates. A similar pH profile was observed in the presence of excipients, although the excipients alter the overall stability profile. Additional accelerated stability studies examined the stabilizers necessary for optimal stability.

CONCLUSIONS

Excipients with the capacity to substitute for water upon dehydration better preserve the native structure resulting in enhanced stability. Those that have high glass transition temperatures provide the highest level of stability during storage, although they do not prevent dehydration induced unfolding.

Production of soluble and active recombinant murine interleukin-2 in Escherichia coli: high level expression, Kil-induced release, and purification

We describe the production of soluble murine interleukin-2 (mIL2) and its purification following regulated release in the growth medium of Escherichia coli. The system is based on the ability of the Kil protein of pMB9 to release periplasmic proteins into the growth medium. As the kil gene is under control of the strong, but well regulatable pL promoter, the kil bearing plasmid is stably maintained in the cell. mIL2, fused to the outer membrane protein A (OmpA) signal peptide, was secreted into the periplasm and subsequently released into the growth medium after induction of the kil gene. This strategy allows a quick and easy purification of the heterologous protein without using strong denaturants or detergents, yielding a native protein with a specific biological activity equal to the natural mIL2. The system permits the production of mIL2 at levels up to 16 mg/liter. From a 12-liter fermentation, a final yield of about 30 mg of pure mIL2 was obtained.

Purification of human interleukin-2 using the cellulose-binding domain of a prokaryotic cellulase

Engineering gene fusions which introduce an affinity tag linked to the target polypeptide by a specific protease cleavage site is widely used to facilitate recombinant protein purification. A fusion protein CBDAPT-IL-2, comprised of the cellulose-binding domain (CBD) and Pro-Thr (PT) rich linker of the Cellulomonas fimi endo-beta-1,4-glucanase A (CenA) and a factor Xa cleavage sequence (IleGluGlyArg) fused to the N terminus of human interleukin-2, was produced in Escherichia coli, Streptomyces lividans and mammalian COS cells. CBDAPT-IL-2, secreted from S. lividans or COS cells or recovered from the insoluble fraction of E. coli, could be purified by adsorption on cellulose. The intact fusion protein adsorbed to cellulose was hydrolyzed in situ with factor Xa to release active interleukin-2.

Purification and characterization of a high-molecular-weight form of recombinant human interleukin-2

During purification of recombinant Interleukin-2 (rIL-2) by reversed-phase HPLC, early fractions are discarded due to the presence of an unidentified form of rIL-2. A procedure has been developed to isolate and purify this unidentified form of rIL-2. The purification process involves two chromatography steps and utilizes a Bakerbond Carboxy-Sulfon (CS) column under two different conditions. This material, designated as a high-molecular-weight form of rIL-2 (HMWrIL-2), exhibits lower mobility during SDS-PAGE and has a pI which is approximately one unit less than that of rIL-2, but has similar bioactivity to rIL-2. Structural analysis through enzymatic cleavage, HPLC peptide mapping, mass spectrometry, sequencing, and amino acid composition revealed that the difference between these two proteins is a C-terminal extension of 11 amino acids. This extension could be the result of a nonstandard translation event.

Mammalian cell expression of single-chain Fv (sFv) antibody proteins and their C-terminal fusions with interleukin-2 and other effector domains

The production of several single-chain Fv (sFv) antibody proteins was examined by three modes of mammalian cell expression. Our primary model was the 741F8 anti-c-erbB-2 sFv, assembled as either the VH-VL or VL-VH, and expressed alone, with C-terminal cysteine for dimerization, or as fusion proteins with carboxyl-terminal effector domains, including interleukin-2, the B domain of staphylococcal protein A, the S-peptide of ribonuclease S, or hexa-histidine metal chelate peptide. Constructs were expressed and secreted transiently in 293 cells and stably in CHO or Sp2/0 cell lines, the latter yielding up to 10 mg per liter. Single-chain constructs of MOPC 315 myeloma and 26-10 monoclonal antibodies were also expressed, as were hybrids comprising unrelated VH and VL regions. Our results suggest that mammalian expression is a practical and valuable complement to the bacterial expression of single-chain antibodies.

Fluidized-bed receptor-affinity chromatography

A multipurpose fluidized-bed receptor-affinity purification system based upon the biological recognition between an immobilized receptor and its soluble protein ligands is described. The fluidized affinity sorbent consists of a soluble form of interleukin-2 receptor chemically bonded to an aldehyde derivative of controlled pore glass beads, which have a pore diameter of 1000 A and a particle density of 1.2-1.3 g/mL. The fluidized-bed separation device used in this study consists of a specially designed column fitted at the inlet end with a perforated distributor plate covered with a screen and the top outlet with an adjustable piston. The fluidized-bed consisting of a loose gel matrix permits the unimpeded passage of cell debris and particulate matter, while the target protein is captured by the affinity beads. Purification of the humanized-anti-Tac monoclonal antibody is used as a model system to determine the operational parameters. Also, fluidized-bed receptor-affinity chromatography has been successfully employed in the purification of recombinant interleukin-2 and single chain anti-Tac(Fv)-Pseudomonas exotoxin immunotoxin from unclarified inclusion body extracts. Overall, fluidized-bed receptor-affinity chromatography is found to be a productive affinity method suitable for the purification of recombinant human interleukin-2 and related molecules.

Overexpression and characterization of recombinant human fusion protein IL-6/IL-2 (CH925)

An expression vector encoding the human recombinant fusion protein interleukin 6/interleukin 2 (IL-6/IL-2) was constructed. When a flexible linker had been synthesized and ligated with the IL-2 gene fragment by polymerase chain reaction (PCR) amplification, the IL-6 gene fragment was unidirectionally inserted into the upstream of the linker-IL-2 sequence. The molecule of the IL-6-linker-IL-2 fusion gene named E. coli DH5 alpha/pfIL-6/2 was cloned and identified by DNA sequencing. The expressed protein named as CH925 showed a strong band on SDS-PAGE and amounted to 32% of total cell protein, and its estimated molecular weight was about 37 kDa. The fusion protein purified by gel filtration and reversed-phase HPLC showed as almost homogeneous. CH925 possesses both IL-2 and IL-6 activities when assayed by CTLL2- and 7TD1-dependent cell lines, respectively. The specific activity of IL-2 was 2.1 x 10(6) U/mg while that of IL-6 was 2.3 x 10(8) U/mg. Our studies exhibited that CH925 exerted a significant augmentative effect on the growth of erythroid colony forming units (CFU-E), and synergized with erythropoietin (EPO) and/or IL-3 in a dose-dependent way. Our experimental results also showed CH925 at a low dose causing active lymphokine-activated killer (LAK) cell proliferation more vigorous than IL-2 and/or IL-6 (p < 0.001). CH925 is a novel fusion protein, being neither IL-6 nor IL-2, more potent than IL-2 and/or IL-6 and causing non-IL-2 and non-IL-6 functions of strong EPO-like and mild IL-3-like effects on erythroid progenitor cell growth. There is a potential for efficacious clinical application of CH925.

Interleukin 2 transcription factors as molecular targets of cAMP inhibition: delayed inhibition kinetics and combinatorial transcription roles

Elevation of cAMP can cause gene-specific inhibition of interleukin 2 (IL-2) expression. To investigate the mechanism of this effect, we have combined electrophoretic mobility shift assays and in vivo genomic footprinting to assess both the availability of putative IL-2 transcription factors in forskolin-treated cells and the functional capacity of these factors to engage their sites in vivo. All observed effects of forskolin depended upon protein kinase A, for they were blocked by introduction of a dominant negative mutant subunit of protein kinase A. In the EL4.E1 cell line, we report specific inhibitory effects of cAMP elevation both on NF-kappa B/Rel family factors binding at -200 bp, and on a novel, biochemically distinct "TGGGC" factor binding at -225 bp with respect to the IL-2 transcriptional start site. Neither NF-AT nor AP-1 binding activities are detectably inhibited in gel mobility shift assays. Elevation of cAMP inhibits NF-kappa B activity with delayed kinetics in association with a delayed inhibition of IL-2 RNA accumulation. Activation of cells in the presence of forskolin prevents the maintenance of stable protein-DNA interactions in vivo, not only at the NF-kappa B and TGGGC sites of the IL-2 enhancer, but also at the NF-AT, AP-1, and other sites. This result, and similar results in cyclosporin A-treated cells, imply that individual IL-2 transcription factors cannot stably bind their target sequences in vivo without coengagement of all other distinct factors at neighboring sites. It is proposed that nonhierarchical, cooperative enhancement of binding is a structural basis of combinatorial transcription factor action at the IL-2 locus.

Analytical performances of commercial ELISA-kits for IL-2, IL-6 and TNF-alpha. A WHO study

The determination of cytokine levels in biological fluids by accurate and sensitive methods is an absolute need to be able to define the involvement of these mediators in various clinical situations. To test if this goal was achieved with ELISA kits, a comparative study was undertaken using various commercial kits (6 for IL-2, 8 for IL-6 and 9 for TNF-alpha). The major aims of the work were to critically analyze the analytical performances of the kits and to illustrate some of the pitfalls the users may face. Substantial differences were noted in terms of sensitivity and behaviour of commercial standards versus international reference preparations. These results clearly illustrate the urgent need for a real standardization of immunoassays for cytokine quantitation.

The ability of peripheral blood mononuclear cells of rabbits infected with Treponema pallidum to produce IL-2

It was previously found that the cell-mediated immune response involved in protection against Treponema pallidum is distinctly suppressed during some periods in the course of syphilis infection in rabbits. This may be a result of the weak ability of cells to produce Interleukin-2 (IL-2) as well as of IL-2 absorption. The ability of peripheral blood mononuclear cells (PBMC) of syphilitic rabbits to produce IL-2 develops within the first two weeks after infection reaching a maximum in about the eleventh week. In infection of longer duration, this capability was distinctly lowered. This low level of activity (no higher than in PBMC of normal rabbits) was maintained for 31 weeks. The ability of PBMC to absorb IL-2, in parallel with its production, was found at the same time in the course of syphilis infection (7-11 weeks). In long-lasting syphilis (more than 12 weeks) both abilities seem to be inhibited. Sera of syphilitic rabbits were found to have a higher level of IL-2 inhibitor than those of normal rabbits. Only in syphilis lasting 9 to 11 weeks, when the production of IL-2 was the greatest, was the level of IL-2 inhibitor nearly the same as in normal rabbit sera. In syphilis lasting longer, the increased level of inhibitor was accompanied by a decreased ability of cells to produce IL-2. These findings suggest that IL-2 inhibitor may be bound to IL-2 or IL-2 receptor on T lymphocytes and in this way would lead to weakening of T cell function and resistance against Treponema pallidum infection.

Vitamin E increases interleukin-2 dependent cellular growth and glycoprotein glycosylation in murine cytotoxic T-cell line

The effect of vitamin E on the modulation of interleukin-2 (IL-2) dependent cellular growth, glycosylation, and expression of certain glycoproteins (GP) was examined in a murine cytotoxic T-cell line (CTLL). CTLL cultures in log phase and growing in 10% IL-2 medium in the presence of 1-16 micrograms vitamin E/ml showed a dose-dependent 2- to 15-fold stimulation of growth (assessed by 3H-thymidine incorporation) relative to controls. Vitamin E-treated cultures were observed to grow more efficiently at lower levels of IL-2 compared to controls. Glycoconjugate biosynthesis (assessed by 3H-galactose incorporation) was stimulated 5- to 15-fold by the addition of vitamin E to the culture medium. GP glycosylation as determined by wheat germ agglutinin binding GP (50-64 Kd) and concanavalin A binding GP (38-200 Kd) increased significantly in the presence of vitamin E. These results demonstrate that vitamin E stimulates IL-2 dependent cellular growth, glycosylation, and expression of certain GP in CTLL.

Purification of interleukin-2 antibodies from healthy individuals

By covalent binding of recombinant interleukin-2 (rIL-2) to Sepharose, it was possible to immunopurify specific human anti-IL-2 antibodies from a pool of immunoglobulins obtained from healthy subjects. Since low quantities of the ligand released by the matrix could interfere with the evaluation of the biological activity of anti-IL-2 antibodies, the antibody preparation was subjected to pepsin digestion which is known to destroy the IL-2 molecule. Purified human anti-IL-2 antibodies were found to be mostly IgG1 and able to neutralize IL-2 induced peripheral blood lymphocytes (PBL) proliferation in vitro. The availability of purified anti-IL-2 antibodies, obtained from healthy individuals, able to modulate IL-2 activity, could be important in several therapeutic approaches.

High-level expression, purification, and renaturation of recombinant murine interleukin-2 from Escherichia coli

A murine interleukin-2 (mIL-2)-encoding cDNA, isolated from a stimulated EL4 mRNA library, was used to construct several expression plasmids directing synthesis of the mature protein in Escherichia coli. The expression was under control of either the PTrp or the PL promoter. Using these systems, a high-level expression of between 10 and 35% of the total cellular protein was obtained. The mIL-2 protein, present as insoluble inclusion bodies, could be solubilized in a chaotropic mixture and was partially purified by preparative gel filtration under denaturing conditions. After renaturation, the protein was further purified to homogeneity by anion-exchange chromatography. Depending on the fermentation, induction, and renaturation conditions, the yield ranged between 0.35 and 1 mg of purified mIL-2/g wet cells. The specific biological activity was about 10(7) units/mg and the endotoxin content < 4 ng/mg pure recombinant protein.