Development of RNA/DNA Hydrogel Targeting Toll-Like Receptor 7/8 for Sustained RNA Release and Potent Immune Activation.

Guanosine- and uridine-rich single-stranded RNA (GU-rich RNA) is an agonist of Toll-like receptor (TLR) 7 and TLR8 and induces strong immune responses. A nanostructured GU-rich RNA/DNA assembly prepared using DNA nanotechnology can be used as an adjuvant capable of improving the biological stability of RNA and promoting efficient RNA delivery to target immune cells. To achieve a sustained supply of GU-rich RNA to immune cells, we developed a GU-rich RNA/DNA hydrogel (RDgel) using nanostructured GU-rich RNA/DNA assembly, from which GU-rich RNA can be released in a sustained manner. A hexapod-like GU-rich RNA/DNA nanostructure, or hexapodRD6, was designed using a 20-mer phosphorothioate-stabilized GU-rich RNA and six phosphodiester DNAs. Two sets of hexapodRD6 were mixed to obtain RDgel. Under serum-containing conditions, GU-rich RNA was gradually released from the RDgel. Fluorescently labeled GU-rich RNA was efficiently taken up by DC2.4 murine dendritic cells and induced a high level of tumor necrosis factor-α release from these cells when it was incorporated into RDgel. These results indicate that the RDgel constructed using DNA nanotechnology can be a useful adjuvant in cancer therapy with sustained RNA release and high immunostimulatory activity.

HDX-MS reveals dysregulated checkpoints that compromise discrimination against self RNA during RIG-I mediated autoimmunity.

Retinoic acid inducible gene-I (RIG-I) ensures immune surveillance of viral RNAs bearing a 5'-triphosphate (5'ppp) moiety. Mutations in RIG-I (C268F and E373A) lead to impaired ATPase activity, thereby driving hyperactive signaling associated with autoimmune diseases. Here we report, using hydrogen/deuterium exchange, mechanistic models for dysregulated RIG-I proofreading that ultimately result in the improper recognition of cellular RNAs bearing 7-methylguanosine and N1-2'-O-methylation (Cap1) on the 5' end. Cap1-RNA compromises its ability to stabilize RIG-I helicase and blunts caspase activation and recruitment domains (CARD) partial opening by threefold. RIG-I H830A mutation restores Cap1-helicase engagement as well as CARDs partial opening event to a level comparable to that of 5'ppp. However, E373A RIG-I locks the receptor in an ATP-bound state, resulting in enhanced Cap1-helicase engagement and a sequential CARDs stimulation. C268F mutation renders a more tethered ring architecture and results in constitutive CARDs signaling in an ATP-independent manner.

Guanosine and its modified derivatives are endogenous ligands for TLR7.

Toll-like receptor (TLR) 7and 8 were considered to recognize single-strand RNA (ssRNA) from viruses. Although these receptors also respond to synthetic small chemical ligands, such as CL075 and R848, it remains to be determined whether these receptors sense natural small molecules or not. In the structure of human TLR8 (huTLR8) with ssRNA, there are two ligand-binding sites: one binds a uridine and the other binds an oligoribonucleotide (ORN). This finding demonstrates that huTLR8 recognizes degradation products of ssRNA, suggesting the presence of natural small ligands. We here show that TLR7 works as the sensor for guanosine (G)/2'-deoxyguanosine (dG) in the presence of ORN where ORN strengthens TLR7 interaction with G/dG. In addition, modified nucleosides such as 7-methylguanosine, 8-hydroxyguanosine (8-OHG) and 8-hydroxydeoxyguanosine (8-OHdG) activated TLR7 with ORNs. Importantly, 8-OHdG-a well-known oxidative DNA damage marker with unknown function-induced strong cytokine production comparable to G and dG both in mouse and human immune cells. Although 8-OHdG bound TLR7/ORN with lower affinity than dG did in isothermal titration calorimetry, administered 8-OHdG was metabolically more stable than dG in the serum, indicating that 8-OHdG acts on TLR7 as an endogenous ligand in vivo To address a role of G analogs in the disease state, we also examined macrophages from Unc93b1 (D34A/D34A) mice, which suffer from TLR7-dependent systemic inflammation, and found that Unc93b1 (D34A/D34A) macrophages showed significantly enhanced response to G alone or 8-OHdG with ORN. In conclusion, our results provide evidence that G, dG, 8-OHG and 8-OHdG are novel endogenous ligands for TLR7.

TLR3 and TLR7 are involved in expression of IL-23 subunits while TLR3 but not TLR7 is involved in expression of IFN-beta by Theiler's virus-infected RAW264.7 cells.

Theiler's murine encephalomyelitis virus (TMEV) infects macrophages and causes demyelinating disease (DD) in certain mouse strains. IL-23 p19/p40 and IFN-beta, which are both expressed by macrophages in response to TMEV, could contribute to or prevent DD. Because TMEV may induce macrophages' cytokines through TLR3 and TLR7 (toll-like receptors), their role in TMEV-induced IL-23 and IFN-beta expression by the RAW264.7 macrophage cell line was determined following infection with TMEV or stimulation with the poly (I:C) or loxoribine. TMEV infection or stimulation with poly (I:C), a TLR3 agonist, or loxoribine, a TLR7 agonist, induced expression of IL-23 and IFN-beta in RAW264.7 cells. In addition, TMEV infection increased expression of TLR3 and TLR7 in RAW264.7 cells. Transfection of RAW264.7 cells with shRNA plasmid vectors expressing siRNA specific for TLR3 or TLR7 concomitantly decreased expression of TLR3 or TLR7, respectively, and TMEV-induced p19 mRNA, p19 protein, and IL-23 p19/p40. Transfection with TLR7-shRNA plasmids reduced expression of TMEV-induced p40 mRNA and p40 protein. However, transfection with TLR3-shRNA plasmids increased expression of TMEV-induced p40 mRNA but decreased p40 protein. In addition, transfection with TLR3-shRNA plasmids but not TLR7-shRNA plasmids decreased expression of TMEV-induced IFN-beta mRNA. Thus TLR3 and TLR7 contribute to TMEV-induced IL-23 p19 and p40, while TLR3 contributes to TMEV-induced IFN-beta.

Toll-like receptor agonists stimulate differential functional activation and cytokine and chemokine gene expression in heterophils isolated from chickens with differential innate responses.

Heterophils isolated from distinct broilers (lines A and B) differ in function and cytokine gene expression profiles. Nothing is known about Toll-like receptor (TLR) expression nor functional activation and cytokine/chemokine gene expression of line A and B heterophils when stimulated with TLR agonists. We found that line A and B heterophils express the same range of TLRs. All the bacterial TLR agonists, peptidoglycan, the synthetic lipoprotein Pam3CSK4, ultra-pure lipopolysaccharide, and flagellin all induced significantly greater functional activation of heterophils from line A compared to B. Only stimulation with the guanosine analog, loxoribine, (LOX) induced a significantly greater functional response in B over A. Additionally, all heterophils from line A stimulated with the bacterial TLR agonists had dramatic upregulation of pro-inflammatory cytokine and chemokine mRNA expression, whereas heterophils from line B had little or no upregulation of these genes. However, stimulation of all heterophils from line B with the bacterial TLR agonists and LOX induced a significant upregulation of IFN-alpha, with little transcription of this cytokine gene in line A heterophils. These findings suggest that the difference in heterophil functional efficiency between these parent lines is due to recognition of pathogens and activation of signaling pathways that induce innate cytokine and chemokine responses.

Antiguanosine antibodies in murine and human lupus have the internal image of G-binding proteins.

OBJECTIVE: To examine the binding specificities of serum IgG antibodies of mouse and human origin directed against guanosine. The immunodominance of guanosine compared with the other nucleosides was established in the MRL/lpr murine model of systemic lupus erythematosus (SLE). Serum antiguanosine autoantibodies in human lupus correlate with nephritis and polyserositis in acute disease as well as in exacerbations of disease symptoms. METHODS: Antiguanosine autoantibodies obtained from humans with SLE were compared to a murine monoclonal antiguanosine antibody, 4H2. The fine specificity of the antiguanosine-binding site was determined by methylation of specific positions on the guanosine molecule and using defined analogs in competitive ELISA. RESULTS: Competitive inhibition assays revealed that serum antiguanosine antibodies bind across the 1 and 7 positions of the guanosine molecule (p < 0.01) and that an oxygen is necessary at position 6 in the molecule. 4H2 exhibited the same binding specificity for guanosine as human polyclonal antiguanosine antibodies, showing a conserved epitope across species. When the fine specificity was compared with known epitopes, the antiguanosine antibodies were found to have the internal image of a G-binding protein, identical to that of the Ha-ras oncogene product p21. CONCLUSION: The finding that antiguanosine autoantibodies vary directly with specific features of SLE, especially nephritis and polyserositis, suggests that they may contribute to the pathology of SLE. Our findings that antiguanosine antibodies have G-binding protein active site homology support the possibility that this species of antibody might interfere with cell signal transduction.

Monoclonal antibody to single-stranded DNA: a potential tool for DNA repair studies.

Growing evidence suggests that DNA repair capacity is an important factor in cancer risk and is therefore essential to assess. Immunochemical assays are amenable to the detection of repair products in complex matrices, such as urine, facilitating noninvasive measurements, although diet and extra-DNA sources of lesion can confound interpretation. The production of single-stranded, lesion-containing DNA oligomers characterises nucleotide excision repair (NER) and hence defines the repair pathway from which a lesion may be derived. Herein we describe the characterisation of a monoclonal antibody which recognises guanine moieties in single-stranded DNA. Application of this antibody in ELISA, demonstrated such oligomers in supernatants from repair-proficient cells post-insult. Testing of urine samples from volunteers demonstrated a relationship between oligomer levels and two urinary DNA damage products, thymine dimers and 8-oxo-2'-deoxyguanosine, supporting our hypothesis that NER gives rise to lesion-containing oligomers which are specific targets for the investigation of DNA repair.

Poly-guanosine motifs costimulate antigen-reactive CD8 T cells while bacterial CpG-DNA affect T-cell activation via antigen-presenting cell-derived cytokines.

Pathogen-derived pattern recognition ligands like lipopolysaccharide (LPS) and bacterial cytidine-guanosine (CpG)-DNA not only activate dendritic cells and macrophages but are also mitogenic for B cells. Less clear are the claimed effects of CpG-DNA on T cells, which range from direct activation, costimulation, or indirect transient activation via antigen-presenting cell (APC)-derived interferon type I (IFN type I). Here we demonstrate that CpG-DNA sequence specifically triggers macrophages to produce IFN type I, interleukin (IL)-12, IL-6 and tumour necrosis factor (TNF), but lacks the ability to directly costimulate T cells. Strikingly, poly-guanosine (poly-G) extensions to CpG-containing oligonucleotides (ODN) abolished the macrophage stimulatory potential yet generated T-cell costimulatory activities. In fact, independently of CpG-motifs, poly-G-ODN displayed the ability to costimulate T cells. Costimulation was operative on CD8 T cells but not CD4 T cells. Poly-G-mediated costimulation resulted in IL-2-driven T-cell proliferation and induced cytolytic T cells. Overall the data imply that poly-G motifs costimulate antigen reactive CD8 T cells, while CpG-DNA motifs fail to do so but may affect T-cell activation via APC derived cytokines such as IFN type I.

Further evidence for a possible role of conformation in the immunogenicity and antigenicity of the oxidative DNA lesion, 8-oxo-2'deoxyguanosine.

Damage to DNA by reactive oxygen species is acknowledged to be an important factor in a number of pathological conditions, including ageing and carcinogenesis. As a consequence, the development of methods for the sensitive detection and quantitation of oxidative DNA lesions has been of paramount importance. The oxidatively modified base product which has achieved most attention is 8-oxodeoxyguanosine (8-oxodG) and is a recognised marker of oxidative DNA damage. Although both polyclonal and monoclonal antibodies have previously been raised to 8-oxodG these have, for the most part failed to recognise this lesion within the DNA polymer. We have, through dilution cloning, produced a monoclonal antibody which appears to preferentially recognise 8-oxodG over deoxyguanosine (dG) in single-stranded oxidatively modified DNA. Such discrimination was not apparent when the DNA was double-stranded. Previous work has shown that 8-oxodG favours the syn glycosidic conformation due to steric repulsion, whereas dG assumes the anti. We present initial data that appear to support the postulate that it is these differences in conformation, in addition to structural recognition of the lesion itself, which are responsible for the discrimination, by our antibody of 8-oxodG over dG in single-stranded DNA.

Antibodies to oxidative DNA damage: characterization of antibodies to 8-oxopurines.

The 8-oxo-7,8-dihydropurines (8-oxopurines) are important cellular premutagenic lesions produced in DNA by free radicals. Specific antibodies were prepared to detect these lesions. For antigens, 8-oxo-7,8-dihydroadenosine (8-oxoAdo) and 8-oxo-7,8-dihydroguanosine (8-oxoGuo) were synthesized from the bromonucleosides, and the immunogens were produced by conjugating these to either bovine serum albumin or rabbit serum albumin by the periodate method. Polyclonal antibodies specific for the haptens were elicited from rabbits immunized with the BSA conjugates. The antibodies to 8-oxoAdo (anti-8-oxoAdo) and 8-oxoGuo (anti-8-oxoGuo) precipitated the homologous antigens in an Ouchterlony gel diffusion assay and no cross-reactivity was observed toward the normal nucleosides or to the heterologous 8-oxopurine. Specificity was also examined by hapten inhibition of antibody reactivity with the homologous conjugates using ELISA. For anti-8-oxoAdo, the IC50 for 8-oxoAdo was 8 mumol/L and 8-bromoadenosine, guanosine, and inosine did not inhibit, even at concentrations of 1.25 mmol/L. Similarly, the IC50 for anti-8-oxoGuo for 8-oxoGuo was 0.1 mumol/L. 8-Methoxyguanosine also inhibited the reaction but was about 500-fold less effective than the eliciting hapten. Other nucleosides tested did not inhibit at concentrations up to 100 mumol/L. Both antibodies could easily detect the corresponding damage in x-irradiated f1 DNA at a dose of 7.5 Gy and both antibodies recognized the corresponding lesion in duplex DNA; however, with anti-8-oxoGuo the signal was reduced about 50% compared to single-stranded DNA. In order to determine the exact amount of each lesion produced in irradiated DNA, and to standardize the ELISA signal, both products were measured after alkaline phosphatase digestion of x-irradiated calf thymus DNA using high-pressure liquid chromatography (HPLC) coupled to an electrochemical detector. Anti-8-oxoGuo could detect ten 8-oxoG residues and anti-8-oxoAdo could detect two 8-oxoA residues per 10,000 nucleotides. Thus, these antibodies should be useful for the detection and measurement of 8-oxopurines in cellular DNA.

Effect of nucleic acid reactive antibodies on tumor cells grown in vivo.

Nucleic acid reactive antibodies have been reported to inhibit various nucleic acid mediated functions in cell free systems. These antibodies were also shown to inhibit the growth of transformed cells in culture due to the high rate of endocytosis in transformed cells as compared to normal cells. In this report, we have tested the possibility of nucleic acid reactive antibodies inhibiting the growth of tumor cells in vivo. The life span of mice bearing Dalton's lymphoma ascites tumor cells was increased, when they were immunized with conjugates of guanosine-BSA, GMP-BSA and tRNA-MBSA complex before transplanting the tumor cells. A similar effect was also observed when mice were injected intraperitoneally with antibodies to guanosine or GMP along with the tumor cells. The specificity was ascertained, as immunization with non-specific antigens did not show any significant effect on tumor bearing mice. The results shows that nucleic acid reactive antibodies inhibit the growth of tumor cells in vivo.

Simultaneous immunoaffinity purification of O6-methyl, O6-ethyl-, O6-propyl- and O6-butylguanine and their analysis by gas chromatography/mass spectrometry.

A sensitive and specific method has been developed for the simultaneous analysis of different O6-alkylguanines. The cross-reactivity of two different antibodies raised against O6-methylguanosine and O6-butylguanosine for a series of O6-alkylguanines was exploited for the immunoaffinity purification of biological samples before quantitative analysis by gas chromatography/mass spectrometry. The method can be applied to the detection of O6-alkylguanines in DNA and appears to be useful for studying chemical carcinogen mechanisms in animals and possibly for the detection of human exposure to alkylating agents.

Enhancement of immunostimulatory activity by dual substitution of C8-substituted guanine ribonucleosides: correlation with increased cytokine secretion.

Guanine ribonucleosides with single substitutions at the C8 position (monosubstituted) or with dual substitutions at the C8 and N7 positions (disubstituted) up-regulate a spectrum of immunologic responses, including cytolytic responses to tumor cells. The current studies were undertaken to determine the effects of dual substitution on a number of nucleoside-inducible immunological parameters. To do so, two monosubstituted analogues, 8-bromoguanosine and 8-mercaptoguanosine, were directly compared with two disubstituted analogues, 7-methyl-8-oxoguanosine and 7-allyl-8-oxoguanosine (loxoribine). All of the compounds enhance natural killer (NK) activity, lymphocyte proliferation, and antibody production in dose-dependent fashion. However, the potency and maximal activity of the disubstituted analogues are considerably greater than those of the monosubstituted analogues. Spleen cells stimulated for 48 h with the disubstituted compounds produce immunoreactive interleukin (IL) 1 alpha, IL-6, tumor necrosis factor-alpha (TNF alpha), and interferon-gamma (IFN gamma). Monosubstituted analogues induce lower quantities of IL-6, TNF alpha, and IFN gamma and fail to induce detectable levels of IL-1 alpha. Total IFN activity, assessed by viral inhibition assay, is also lower for the monosubstituted analogues. Augmentation of antibody secretion by B cells is diminished for neither mono- nor disubstituted compounds upon incubation with anti-cytokine antibodies. In contrast, anti-IFN alpha beta markedly reduces the effects of monosubstituted analogues on NK activity but has less marked effects on NK induction by the disubstituted compounds. A similar pattern of differences is seen for lymphocyte proliferation. Thus, although the analogues induce synthesis of several cytokines, to date only IFN alpha beta appears directly involved in enhancement of NK activity and lymphocyte proliferation. The present data do not, however, exclude the existence of an autocrine stimulatory mechanism not susceptible to inhibition by anti-cytokine antibodies.

Small-molecule immunostimulants. Synthesis and activity of 7,8-disubstituted guanosines and structurally related compounds.

A series of 7,8-disubstituted guanosine derivatives was designed and prepared as potential B-cell-selective activators of the humoral immune response. These compounds were evaluated for their ability to act as B-cell mitogens and to augment the antibody response of B cells to sheep red blood cell (SRBC) challenge (adjuvanticity). In addition, they were tested for their ability to stimulate the natural killer (NK) cell response in murine in vitro cell assays. Certain of the compounds demonstrated in vivo activity when administered either intravenously, subcutaneously, or orally. Analogues with a medium-length alkyl chain (2-4 carbons, 5-7) on the 7-position of 7-alkyl-8-oxoguanosines were found to be particularly potent. Compounds bearing hydroxyalkyl, aminoalkyl, or substituted aminoalkyl substituents on this 7-position were weakly active. However, benzyl groups, including those substituted with heteroatoms (e.g., p-nitrobenzyl, 14), were active. Oxo, thioxo, and seleno groups on C-8 of the guanosine ring all imparted strong activity, whereas other larger substituents did not (e.g., N = CN). Stereochemical inversion of the 2'-hydroxyl on the ribose ring in this series, giving arabinose analogue 70, lessened activity. However, removal of the 2'-hydroxyl, either with (64) or without (73) removal of the 3'-hydroxyl, resulted in excellent activity and improved solubility; 64 also displayed good oral in vivo activity as well. A series of ketals involving the 2',3'-hydroxyls were prepared; certain of the nonpolar ketals (e.g., 48) were remarkably active, pointing to an ancillary hydrophobic binding region that can augment activity. 5'-Phosphate derivative 57 was fairly active, and acyclovir analogue 90 displayed good NK-selective activity: other N-9 sugar mimetics were also active (97-104), although this activity did not carry over into the human B-cell assay. A total of 80 compounds were prepared and evaluated for their immunostimulating activity. Within this group, compounds could be divided into those that were active in all three assays, those that displayed some measure of selectivity for the adjuvanticity assay, and those that preferentially activated NK responses. Because of its overall biological profile and ease of synthesis, 7-allyl-8-oxoguanosine (6; loxoribine, RWJ-21757) was chosen for further development. It is among the most potent compounds evaluated in the three biological assays.

Successful immunotherapy of murine melanoma metastases with 7-thia-8-oxoguanosine.

We have recently reported that a synthetic nucleoside, 7-thia-8-oxoguanosine (7T8OG) is a potent activator of a number of effectors which are involved in anti-tumor immune responses. 7T8OG was found to induce interferon (IFN) production, to activate asialo-GM1 positive (AGM+1) killer cells, and to enhance specific antibody responses. In the present study, we investigated the effect of 7T8OG on growth of the murine pulmonary B16 melanoma and on formation of metastases. C57BL/6 mice were injected i.p. with 50-150 mg/kg 7T8OG before or after i.v. inoculation of B16 melanoma tumor cells, and 17-19 days after tumor inoculation, the number of metastases in the lungs were counted. 7T8OG given systemically in a single or a divided dose 24 h prior to the challenge of tumor cells reduced the number of lung tumor metastases by 89-99% which is highly significant as compared to untreated control (P less than 0.001). Occasional extra pulmonary tumor growth in the thoracic cavity and neck lymph node was also completely inhibited. The reduction in the number of tumor nodules was dose dependent. A single dose of 150 mg/kg of 7T8OG was also effective in inhibiting the growth of 3-5 day old metastatic tumors. The cytotoxic activity of killer cells induced in vivo by 7T8OG was completely abolished by in vitro treatment of cells with anti-AGM1 antibody plus complement. Administration of anti-AGM1 antibody following the 7T8OG treatment completely abrogated the anti-tumor effect of 7T8OG, resulting in a massive increase in the number of tumor foci in the lungs. Administration of carageenan or silica followed by injection of 7T8OG caused a significant increase (P less than 0.01) in the number of pulmonary tumor nodules compared to treatment with 7T8OG only. These findings indicate that activated macrophages or perhaps their cytokine (tumor necrosis factor) also contribute to the host tumor defense by 7T8OG.

Calibration of target amounts of DNA in hybridization experiments using monoclonal anti-nucleoside antibodies.

Two anti-nucleoside monoclonal antibodies (A-16 and G-K21) were raised after immunizing mice with adenosine or guanosine coupled to bovine serum albumin by periodate oxidation. They were selected for their ability to detect these immunogens and single-stranded DNA in an enzyme-linked immunosorbent assay test. The antibodies were purified from ascitic fluids, their isotypes were determined and their ability to detect DNAs and RNAs on nitrocellulose membranes was tested. They belonged to the IgG1 subclass and were both able to recognize picogram amounts of single-stranded DNAs on nitrocellulose sheets, whatever the origin of the nucleic acid, but were unable to detect RNA efficiently. The same monoclonal antibodies were used to estimate minute amounts of target staphylococci DNAs to permit standardization of non-radioactive hybridization experiments for detection of antibiotic resistance genes.

Probing the surface of Z-DNA with anti-nucleoside antibodies.

Antibodies specific for cytidine (C) and guanosine (G) were used to probe the surface of two Z-DNA conformers. When tested by ELISA, anti-G reacted with poly(dG-dC).poly(dG-dC) treated with bromine water [Br-poly(dG-dC).poly(dG-dC)] but anti-C did not. A weak reaction with anti-C was detected by dot immunobinding. In contrast, anti-C reacted strongly with poly(dG-dC).poly(dG-dC) treated with N-acetoxy-2-(acetylamino)fluorene [AAF-poly(dG-dC).poly(dG-dC)]; anti-G reacted weakly, despite the fact that most G residues had not been substituted with AAF. Neither antinucleoside bound to the B conformation of poly(dG-dC).poly(dG-dC). In competition experiments, GMP was the most efficient competitor of the reaction of anti-G with Br-poly(dG-dC).poly(dG-dC); AMP and TMP were 100-fold less efficient, and CMP did not compete to a significant extent. In contrast, the reaction of anti-Z with Br-poly(dG-dC).poly(dG-dC) was not inhibited by nucleotides. Of five possible sites recognized on guanosine by anti-G antibodies (N1, C6, O6, N7, and C8), AMP and TMP share three or their equivalent and CMP only one. The binding of anti-C to AAF-poly(dG-dC).poly(dG-dC) was inhibited best by CMP; AMP was 8 times less efficient; GMP and TMP were about 35-fold less efficient than CMP. Thus, although the amino group on the C4 position of CMP appears to be immunodominant, the capacity of GMP and TMP to inhibit the reaction indicates that other sites are also recognized in AAF-poly(dG-dC).poly(dG-dC), e.g., the exposed C5 position.(ABSTRACT TRUNCATED AT 250 WORDS)

Establishment of a nucleoside-specific suppressor T cell line from SLE prone (NZB/NZW)F1 mice.

A long-term cultured suppressor T cell line (GTS-124) was established from an autoimmune mouse strain, (NZB X NZW)F1, by a two-part procedure: a) B/W F1 mice were made tolerant to guanosine (G) by administration of a tolerogen, the G-modified copolymer of D-glutamic acid and D-lysine (G-D-GL); and b) the spleen cells obtained from tolerant mice were repeatedly stimulated with mitomycin C-treated G-modified syngeneic spleen cells. The GTS-124 cells suppressed the secondary in vitro response to G-keyhole limpet hemocyanin (G-KLH) but did not suppress the response to unrelated antigens, sheep erythrocytes (SRBC), or trinitrophenyl-KLH (TNP-KLH). The expression of Thy-1 antigen on the cell surface of GTS-124 was demonstrated by flow cytometry. Growth of GTS-124 cells was dependent on IL 2. To determine whether GTS-124 cells could suppress the response to nucleosides other than G, KLH coupled with four nucleosides (adenosine [A], G, cytidine [C], and thymine riboside [T]) collectively (AGCT-KLH) was first used as the antigen in the assay system. The PFC response to the individual nucleosides (anti-A, -G, -C, and -T PFC) were effectively inhibited by GTS-124 cells, suggesting that the GTS-124 cells mediated cross-suppression toward all four nucleosides. A more stringent cross-suppression test was conducted by using only the T moiety bound to KLH (T-KLH) as antigen. The results showed that GTS-124 cells were capable of suppressing the T-specific response. The cross-suppression could be seen after repeated selection on a G-BSA-coated dish. These results provide direct evidence that the suppressor T cells induced by in vitro stimulation with G-modified self can indeed suppress the response to nucleosides other than G.