Bacterial tRNA 2'-O-methylation is dynamically regulated under stress conditions and modulates innate immune response.

RNA modifications are a well-recognized way of gene expression regulation at the post-transcriptional level. Despite the importance of this level of regulation, current knowledge on modulation of tRNA modification status in response to stress conditions is far from being complete. While it is widely accepted that tRNA modifications are rather dynamic, such variations are mostly assessed in terms of total tRNA, with only a few instances where changes could be traced to single isoacceptor species. Using Escherichia coli as a model system, we explored stress-induced modulation of 2'-O-methylations in tRNAs by RiboMethSeq. This analysis and orthogonal analytical measurements by LC-MS show substantial, but not uniform, increase of the Gm18 level in selected tRNAs under mild bacteriostatic antibiotic stress, while other Nm modifications remain relatively constant. The absence of Gm18 modification in tRNAs leads to moderate alterations in E. coli mRNA transcriptome, but does not affect polysomal association of mRNAs. Interestingly, the subset of motility/chemiotaxis genes is significantly overexpressed in ΔTrmH mutant, this corroborates with increased swarming motility of the mutant strain. The stress-induced increase of tRNA Gm18 level, in turn, reduced immunostimulation properties of bacterial tRNAs, which is concordant with the previous observation that Gm18 is a suppressor of Toll-like receptor 7 (TLR7)-mediated interferon release. This documents an effect of stress induced modulation of tRNA modification that acts outside protein translation.

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.

Efficacy of CpG-ODN Administration Routes on Humoral Responses against Newcastle disease in Broilers.

Un-methylated cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODN) has been considered as a powerful vaccine adjuvant and recognition of CpG-ODN by chicken leukocytes promotes their ability to fight against infections. In our study, efficacy of different routes of CpG-ODN application as an adjuvant on immune responses (antibody titer together with leukogram) following vaccination against Newcastle disease (ND) has been evaluated in broiler chickens (Ross-308). The results indicated that routes of CpG-ODN administration influence immune responses and comparison effectiveness of CpG-OND delivery routes showed that group vaccinated by eye-drop application had the highest antibody titer than that of the group injected intramuscularly (im) and the difference was significant (p = 0.04) on day 35 of age. Antibody titer of the group treated with Clone 30 plus CpG-ODN via eye-drop route was higher than that of the group vaccinated with clone 30 alone on days 28 and 35 of age and the difference was significant (p = 0.04). Co-administration of both vaccine and CpG improved outcome of leukogram of the chickens on days 21 to 42 of age and among the treated groups, WBC of the group received both vaccine and CpG by eye-drop route significantly (p < 0.05) differed from that of the group vaccinated with clone 30 alone on days 28 and 35 but not on day 42 of age. Average final body weight of the control group did not significantly differ from those of the treated groups at end of the experiment. In conclusion, co-administration of ND vaccine plus CpG-ODN via eye-drop route improves immune responses.

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.

Double methylation of tRNA-U54 to 2'-O-methylthymidine (Tm) synergistically decreases immune response by Toll-like receptor 7.

Sensing of nucleic acids for molecular discrimination between self and non-self is a challenging task for the innate immune system. RNA acts as a potent stimulus for pattern recognition receptors including in particular human Toll-like receptor 7 (TLR7). Certain RNA modifications limit potentially harmful self-recognition of endogenous RNA. Previous studies had identified the 2'-O-methylation of guanosine 18 (Gm18) within tRNAs as an antagonist of TLR7 leading to an impaired immune response. However, human tRNALys3 was non-stimulatory despite lacking Gm18. To identify the underlying molecular principle, interferon responses of human peripheral blood mononuclear cells to differentially modified tRNALys3 were determined. The investigation of synthetic modivariants allowed attributing a significant part of the immunosilencing effect to the 2'-O-methylthymidine (m5Um) modification at position 54. The effect was contingent upon the synergistic presence of both methyl groups at positions C5 and 2'O, as shown by the fact that neither Um54 nor m5U54 produced any effect alone. Testing permutations of the nucleobase at ribose-methylated position 54 suggested that the extent of silencing and antagonism of the TLR7 response was governed by hydrogen patterns and lipophilic interactions of the nucleobase. The results identify a new immune-modulatory endogenous RNA modification that limits TLR7 activation by RNA.

Nucleotide Composition of Human Ig Nontemplated Regions Depends on Trimming of the Flanking Gene Segments, and Terminal Deoxynucleotidyl Transferase Favors Adding Cytosine, Not Guanosine, in Most VDJ Rearrangements.

The formation of nontemplated (N) regions during Ig gene rearrangement is a major contributor to Ab diversity. To gain insights into the mechanisms behind this, we studied the nucleotide composition of N regions within 29,962 unique human VHDJH rearrangements and 8728 unique human DJH rearrangements containing exactly one identifiable D gene segment and thus two N regions, N1 and N2. We found a distinct decreasing content of cytosine (C) and increasing content of guanine (G) across each N region, suggesting that N regions are typically generated by concatenation of two 3' overhangs synthesized by addition of nucleoside triphosphates with a preference for dCTP. This challenges the general assumption that the terminal deoxynucleotidyl transferase favors dGTP in vivo. Furthermore, we found that the G and C gradients depended strongly on whether the germline gene segments were trimmed or not. Our data show that C-enriched N addition preferentially happens at trimmed 3' ends of VH, D, and JH gene segments, indicating a dependency of the transferase mechanism upon the nuclease mechanism.

Structural Analysis Reveals that Toll-like Receptor 7 Is a Dual Receptor for Guanosine and Single-Stranded RNA.

Toll-like receptor 7 (TLR7) is a single-stranded RNA (ssRNA) sensor in innate immunity and also responds to guanosine and chemical ligands, such as imidazoquinoline compounds. However, TLR7 activation mechanism by these ligands remain largely unknown. Here, we generated crystal structures of three TLR7 complexes, and found that all formed an activated m-shaped dimer with two ligand-binding sites. The first site conserved in TLR7 and TLR8 was used for small ligand-binding essential for its activation. The second site spatially distinct from that of TLR8 was used for a ssRNA-binding that enhanced the affinity of the first-site ligands. The first site preferentially recognized guanosine and the second site specifically bound to uridine moieties in ssRNA. Our structural, biochemical, and mutagenesis studies indicated that TLR7 is a dual receptor for guanosine and uridine-containing ssRNA. Our findings have important implications for understanding of TLR7 function, as well as for therapeutic manipulation of TLR7 activation.

Alteration of the cytokine signature by various TLR ligands in different T cell populations in MOG37-50 and MOG35-55-induced EAE in C57BL/6 mice.

Interleukin 17 (IL-17), produced by T cells, plays an important role in Multiple Sclerosis (MS) and its animal model, Experimental Autoimmune Encephalomyelitis (EAE). In contrast to IL-17-producing CD4+ T cells, the contribution of IL-17-producing CD8+ T cells (Tc17) in CNS autoimmunity has been investigated less intensively. Here we investigate the role of TC17 in EAE. We compare different T cell populations and their cytokine pattern in the MOG35-55- and MOG37-50-induced EAE. We detected a similar cytokine phenotype for both EAE models in the autoimmune process assessed at different stages. Regarding the migratory activity, an involvement of IL-17 and IFN-γ in disease onset was suggested. Furthermore, we show that PAMPs have the ability to drive autoimmune process. To modify the cytokine pattern of different T cell populations, a combination of distinct factors is required (the activation of MyD88 or Syk, the genetic background, the presence of APCs and CD4+ T cells).

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.

Adjuvant effect of cationic liposomes and CpG depends on administration route.

In this study we explored the immunization route-dependent adjuvanticity of cationic liposomes loaded with an antigen (ovalbumin; OVA) and an immune potentiator (CpG). Mice were immunized intranodally, intradermally, transcutaneously (with microneedle pre-treatment) and nasally with liposomal OVA/CpG or OVA/CpG solution. In vitro, OVA/CpG liposomes showed enhanced uptake by DCs of both OVA and CpG compared to OVA+CpG solution. A similar enhanced uptake by DCs was observed in vivo when fluorescent OVA/CpG liposomes were administered intranodally. However, after transcutaneous and nasal application a lower uptake of OVA/CpG liposomes compared to an OVA+CpG solution was observed. Moreover, the IgG titers after nasal and transcutaneous administration of OVA/CpG liposomes were reduced compared to administration of an OVA+CpG solution. Although serum IgG titers may suggest limited added value of liposomes to the immunogenicity, for all routes, OVA/CpG liposomes resulted in elevated IgG2a levels, whereas administration of OVA+CpG solutions did not. These data show that encapsulation of antigen and adjuvant into a cationic liposome has a beneficial effect on the quality of the antibody response in mice after intranodal or intradermal immunization, but impairs proper delivery of antigen and adjuvant to the lymph nodes when the formulations are administered transcutaneously or nasally.

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.

Serum antiguanosine antibodies as a marker for SLE disease activity and pathogen potential.

BACKGROUND: This article reviews research conducted on the immunogenicity of the nucleosides of DNA, especially guanosine, the most immunologically active nucleoside. Discussed is the relationship between circulating antibodies to guanosine, their potential role in SLE disease activity, the binding properties of monoclonal antiguanosine antibody (4H2) compared to polyclonal antiguanosine antibodies in humans with SLE, cell membrane penetration by these antibodies and their interference with signal transduction possibly related to their binding to mitochondria and their apparent GTPase activity. METHODS: Enzyme-linked immunosorbent assay methodology was used to show clinical relationships between antiguanosine antibody levels and disease activity in SLE. These results are discussed along with methods of detecting cell penetration by this antibody using special staining techniques, laser-scanning microscope detection of mitochondrial localization, and interference of cAMP and pKA production/activation. Additionally, there is some discussion regarding the assay used to detect enzymatic activity of antiguanosine antibodies. RESULTS: Enhanced circulating levels of antiguanosine antibodies in patients with SLE correlate closely with SLE disease activity. Other factors are discussed that support the pathogenic potential of these antibodies, including their ability to penetrate lymphocytes, bind to mitochondria, inactivate mitochondrial function, interfere with signal transduction, and their potential enzymatically activity. CONCLUSIONS: Antiguanosine antibodies correlate with SLE disease activity and may be pathogenically important in SLE by interfering with signal transduction, inactivating mitochondrial and cell function in patients with SLE.

Poly-guanosine strings improve cellular uptake and stimulatory activity of phosphodiester CpG oligonucleotides in human leukocytes.

CpG-oligonucleotides (CpG-ODN) have been shown to exert strong immuno-stimulatory effects through activation of Toll-like receptor 9 (TLR-9). However, TLR-9 triggering takes place in endosomal compartments and thus CpG-ODN have to be taken up prior to signal transduction. We here report that 3'-poly-guanosine strings can improve cellular internalisation of phosphodiester but not of phosphorothioate CpG-ODN. Improved cellular uptake correlated with enhanced IL-6 secretion and proliferation of PBMC. Also, TLR-9 transfected HEK293 cells were activated more efficiently by poly-guanosine modified CpG-ODN. The results indicate that the synthesis of stimulatory CpG-ODN based on a phosphodiester backbone is feasible via such poly-guanosine substitutions. In addition we observed that phosphorothioate ODN were able to exert immunostimulatory effects independent of the presence of CpG motifs.

Determination of glycated nucleobases in human urine by a new monoclonal antibody specific for N2-carboxyethyl-2'-deoxyguanosine.

Sugars and sugar degradation products react in vivo readily with proteins (glycation) resulting in the formation of a heterogeneous group of reaction products, which are called advanced glycation end products (AGEs). AGEs notably change the structure and function of proteins so that extended protein-AGE formation is linked to complications such as nephropathy, atherosclerosis, and cataract. DNA can be glycated in vitro in a similar way as proteins, and the two diastereomers of N(2)-carboxyethyl-2'-deoxyguanosine (CEdG(A,B)) were identified as major DNA AGEs. It was postulated that DNA AGEs play an important role in aging, diabetes, and uremia. However, at the moment, sensitive methods to measure the extent and impact of DNA AGEs in vivo do not exist. In this study, we developed a monoclonal antibody, which recognized CEdG(A,B) with high affinity and specificity (MAb M-5.1.6). The I(50) value for CEdG(A,B) was 2.1 ng/mL, whereas other modified nuclueobases and AGE proteins showed negligible cross-reactivity. Unmodified 2'-deoxyguanosine was only weakly recognized with an I(50) value > 600,000 ng/mL, which is the limit of solubility. MAb M-5.1.6 was then used to measure the urinary excretion of AGE-modified nucleobases in a competitive enzyme-linked immunosorbent assay. The recovery of CEdG(A,B) from human urine was between 87.4 and 99.7% with coefficients of variations between 8.0 and 22.2%. The detection limit was 0.06 ng/mL, and the determination limit was 0.15 ng/mL with a linear range between 0.3 and 100 ng/mL. CEdG equivalents were analyzed in urine samples from 121 healthy volunteers, and concentrations between 1.2 and 117 ng CEdG equiv/mg creatinine were detected.

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.

Functional coupling of capping and transcription of mRNA.

In humans, 5' m(7)G cap addition is accomplished cotranscriptionally by the sequential action of the capping enzyme (Hce1) and the cap methyltransferase (Hcm1). We found that guanylylation and methylation occur efficiently during transcription with t(1/2)'s of less than 15 and 70 s, respectively. A two to four order of magnitude increase was found in the rate of guanylylation of RNA in transcription complexes compared to free RNA. This stimulation required only the RNA polymerase II elongation complex and Hce1. Capping activity was weakly associated with elongation but not preinitiation complexes. The CTD was not required for functional coupling but stimulated the rate of capping 4-fold. Inhibition of Cdk7 but not Cdk9 similarly slowed the rate of capping.

Circulating antibodies to guanosine in systemic lupus erythematosus: correlation with nephritis and polyserositis by acute and longitudinal analyses.

Systemic lupus erythematosus (SLE) is characterized by autoantibodies, including antibodies to the nucleosides of DNA. Guanosine is the most immunogenic nucleoside. In this study serum antiguanosine antibody levels were compared with disease activity, determined by their SLEDI score, in 86 patients with SLE. Sera from these patients were tested, by ELISA, for autoantibodies to guanosine, single-stranded DNA (ssDNA), and double-stranded DNA (dsDNA). Anti-double-stranded DNA levels were also measured by RIA. Resultant values from these assays were correlated with SLE disease activity, and compared with specific features of SLE. The strongest correlation was higher levels of antiguanosine antibodies in patients with active lupus nephritis and polyserositis compared to patients with inactive disease (P < 0.0001). Antiguanosine levels also correlated with arthritis (P < 0.006), CNS lupus (P < 0.005), and hematologic manifestations of SLE (P < 0.002). To test the validity of this association in chronic SLE, serum antiguanosine antibodies were measured in patients with SLE at various phases of disease activity. Twelve patients with SLE had serum samples drawn at active, active-improved, and inactive phases over a 3-7 y period. Differences were significant for serum antiguanosine antibodies in the active group compared to the inactive group (P < 0.05) and the active vs the active-improved group (P < 0.02), unlike those for dsDNA and ssDNA by ELISA or RIA. Antiguanosine antibodies correlated more closely with disease activity in SLE patients in this longitudinal study than either anti-dsDNA or ssDNA antibodies. Thus, antibodies to guanosine correlated as well or better with disease activity than the other anti-DNA antibodies measured and should be considered to contribute to the pathology of SLE, especially lupus nephritis.

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.