HPRT- mutant T cells in the peripheral blood and synovial tissue of patients with rheumatoid arthritis

Clonality, trafficking, and molecular alterations among Hprt mutant T lymphocytes isolated from control mice versus mice treated with N-ethyl-N-nitrosourea

Mutations in T lymphocytes (T-cells) are informative quantitative markers for environmental mutagen exposures, but risk extrapolations from rodent models to humans also require an understanding of how T-cell development and proliferation kinetics impact mutagenic outcomes. Rodent studies have shown that patterns in chemical-induced mutations in the hypoxanthine-guanine phosphoribosyltransferase (Hprt) gene of T-cells differ between lymphoid organs. The current work was performed to obtain knowledge of the relationships between maturation events during T-cell development and changes in chemical-induced mutant frequencies over time in differing immune compartments of a mouse model. A novel reverse transcriptase-polymerase chain reaction based method was developed to determine the specific T-cell receptor beta (Tcrb) gene mRNA expressed in mouse T-cell isolates, enabling sequence analysis of the PCR product that then identifies the specific hypervariable CDR3 junctional region of the expressed Tcrb gene for individual isolates. Characterization of spontaneous Hprt mutant isolates from the thymus, spleen, and lymph nodes of control mice for their Tcrb gene expression found evidence of in vivo clonal amplifications of Hprt mutants and their trafficking between tissues in the same animal. Concurrent analyses of Hprt mutations and Tcrb gene rearrangements in different lymphoid tissues of control versus N-ethyl-N-nitrosourea-exposed mice permitted elucidation of the localization and timing of mutational events in T-cells, establishing that mutagenesis occurs primarily in the pre-rearrangement replicative period in pre-thymic/thymic populations. These findings demonstrate that chemical-induced mutagenic burden is determined by the combination of mutagenesis and T-cell clonal expansion, processes with roles in immune function and in the pathogenesis of autoimmune disease and cancer.

Molecular characterization of hypoxanthine guanine phosphoribosyltransferase mutant T cells in human blood: The concept of surrogate selection for immunologically relevant cells

Somatic cell gene mutations arise in vivo due to replication errors during DNA synthesis occurring spontaneously during normal DNA synthesis or as a result of replication on a DNA template damaged by endogenous or exogenous mutagens. In principle, changes in the frequencies of mutant cells in vivo in humans reflect changes in exposures to exogenous or endogenous DNA damaging insults, other factors being equal. It is becoming increasingly evident however, that somatic mutations in humans have a far greater range of interpretations. For example, mutations in lymphocytes provide invaluable probes for in vivo cellular and molecular processes, providing identification of clonal amplifications of these cells in autoimmune and infectious diseases, transplantation recipients, paroxysmal nocturnal hemoglobinuria (PNH), and cancer. The assay for mutations of the X-chromosomal hypoxanthine guanine phosphoribosyltransferase (HPRT) gene has gained popular acceptance for this purpose since viable mutant cells can be recovered for molecular and other analyses. Although the major application of the HPRT T cell assay remains human population monitoring, the enrichment of activated T cells in the mutant fraction in individuals with ongoing immunological processes has demonstrated the utility of surrogate selection, a method that uses somatic mutation as a surrogate marker for the in vivo T cell proliferation that underlies immunological processes to investigate clinical disorders with immunological features. Studies encompassing a wide range of clinical conditions are reviewed. Despite the historical importance of the HPRT mutation system in validating surrogate selection, there are now additional mutational and other methods for identifying immunologically active T cells. These methods are reviewed and provide insights for strategies to extend surrogate selection in future studies.

Somatic Variants: New Kids on the Block in Human Immunogenetics

Somatic variants are not inherited but acquired during an individual's lifetime, and individuals are increasingly considered as complex mosaics of genetically distinct cells. Whereas this concept is long-recognized in cancer, this review focuses on the growing role of somatic variants in immune cells in nonmalignant immune-related disorders, such as primary immunodeficiency and autoimmune diseases. Older case reports described somatic variants early in development, leading to large numbers of affected cells and severe phenotypes. Thanks to technological evolution, it is now feasible to detect somatic variants occurring later in life and affecting fewer cells. Hence, only recently is the scale at which somatic variants contribute to monogenic diseases being uncovered and is their contribution to complex diseases being explored systematically.

Regulation of the Cell Cycle and Inflammatory Arthritis by the Transcription Cofactor LBH Gene

Rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) display unique aggressive behavior, invading the articular cartilage and promoting inflammation. Using an integrative analysis of RA risk alleles, the transcriptome and methylome in RA FLS, we recently identified the limb bud and heart development (LBH) gene as a key dysregulated gene in RA and other autoimmune diseases. Although some evidence suggests that LBH could modulate the cell cycle, the precise mechanism is unknown and its impact on inflammation in vivo has not been defined. Our cell cycle analysis studies show that LBH deficiency in FLS leads to S-phase arrest and failure to progress through the cell cycle. LBH-deficient FLS had increased DNA damage and reduced expression of the catalytic subunit of DNA polymerase α. Decreased DNA polymerase α was followed by checkpoint arrest due to phosphorylation of checkpoint kinase 1. Because DNA fragments can increase arthritis severity in preclinical models, we then explored the effect of LBH deficiency in the K/BxN serum transfer model. Lbh knockout exacerbated disease severity, which is associated with elevated levels of IL-1β and checkpoint kinase 1 phosphorylation. These studies indicate that LBH deficiency induces S-phase arrest that, in turn, exacerbates inflammation. Because LBH gene variants are associated with type I diabetes mellitus, systemic lupus erythematosus, RA, and celiac disease, these results suggest a general mechanism that could contribute to immune-mediated diseases.

Synovial inflammation, immune cells and their cytokines in osteoarthritis: a review

OBJECTIVE

Although osteoarthritis (OA) is considered a non-inflammatory condition, it is widely accepted that synovial inflammation is a feature of OA. However, the role of immune cells and their cytokines in OA is largely unknown. This narrative systematic review summarizes the knowledge of inflammatory properties, immune cells and their cytokines in synovial tissues (STs) of OA patients.

DESIGN

Broad literature search in different databases was performed which resulted in 100 articles.

RESULTS

Of 100 articles 33 solely investigated inflammation in OA ST with or without comparison with normal samples; the remaining primarily focussed on rheumatoid arthritis (RA) ST. Studies investigating different severity stages or cellular source of cytokines were sparse. OA ST displayed mild/moderate grade inflammation when investigated by means of haematoxylin and eosin (H&E) staining. Most frequently found cells types were macrophages, T cells and mast cells (MCs). Overall the number of cells was lower than in RA, although the number of MCs was as high as or sometimes even higher than in RA ST. Cytokines related to T cell or macrophage function were found in OA ST. Their expression was overall higher than in normal ST, but lower than in RA ST. Their cellular source remains largely unknown in OA ST.

CONCLUSION

Inflammation is common in OA ST and characterized by immune cell infiltration and cytokine secretion. This inflammation seems quantitatively and qualitatively different from inflammation in RA. Further research is needed to clarify the role of inflammation, immune cells and their cytokines in the pathogenesis of OA.

In vivo 6-thioguanine-resistant T cells from melanoma patients have public TCR and share TCR beta amino acid sequences with melanoma-reactive T cells

In vivo hypoxanthine-guanine phosphoribosyltransferase (HPRT)-deficient T cells (MT) from melanoma patients are enriched for T cells with in vivo clonal amplifications that traffic between blood and tumor tissues. Melanoma is thus a model cancer to test the hypothesis that in vivo MT from cancer patients can be used as immunological probes for immunogenic tumor antigens. MT were obtained by 6-thioguanine (TG) selection of lymphocytes from peripheral blood and tumor tissues, and wild-type T cells (WT) were obtained analogously without TG selection. cDNA sequences of the T cell receptor beta chains (TRB) were used as unambiguous biomarkers of in vivo clonality and as indicators of T cell specificity. Public TRB were identified in MT from the blood and tumor of different melanoma patients. Such public TRB were not found in normal control MT or WT. As an indicator of T cell specificity for melanoma, the >2600 MT and WT TRB, including the public TRB from melanoma patients, were compared to a literature-derived empirical database of >1270 TRB from melanoma-reactive T cells. Various degrees of similarity, ranging from 100% conservation to 3-amino acid motifs (3-mer), were found between both melanoma patient MT and WT TRBs and the empirical database. The frequency of 3-mer and 4-mer TRB matching to the empirical database was significantly higher in MT compared with WT in the tumor (p=0.0285 and p=0.006, respectively). In summary, in vivo MT from melanoma patients contain public TRB as well as T cells with specificity for characterized melanoma antigens. We conclude that in vivo MT merit study as novel probes for uncharacterized immunogenic antigens in melanoma and other malignancies.

Fibroblast-like synoviocytes: key effector cells in rheumatoid arthritis

Rheumatoid arthritis (RA) remains a significant unmet medical need despite significant therapeutic advances. The pathogenesis of RA is complex and includes many cell types, including T cells, B cells, and macrophages. Fibroblast-like synoviocytes (FLS) in the synovial intimal lining also play a key role by producing cytokines that perpetuate inflammation and proteases that contribute to cartilage destruction. Rheumatoid FLS develop a unique aggressive phenotype that increases invasiveness into the extracellular matrix and further exacerbates joint damage. Recent advances in understanding the biology of FLS, including their regulation regulate innate immune responses and activation of intracellular signaling mechanisms that control their behavior, provide novel insights into disease mechanisms. New agents that target FLS could potentially complement the current therapies without major deleterious effect on adaptive immune responses.

Activation of nitric oxide signaling by the rheumatoid arthritis shared epitope

OBJECTIVE

Susceptibility to rheumatoid arthritis (RA) is closely associated with HLA-DRB1 alleles encoding a shared epitope (SE) in positions 70-74 of the HLA-DRbeta chain. The mechanistic basis for this association is unknown. Given the proposed pathogenic role of nitric oxide (NO) in RA, this study was undertaken to examine whether the SE can trigger NO signaling events.

METHODS

The intracellular levels of NO were measured with the fluorescent NO probe 4,5-diaminofluorescein diacetate and by the 2,3-diaminonaphthalene method. NO synthase activity was determined by measuring the rate of conversion of radioactive arginine to citrulline. Levels of cGMP were measured with a commercial enzyme-linked immunosorbent assay, and the cytolytic activity of T cells was measured using a standard (51)Cr release assay.

RESULTS

Lymphoblastoid B cell lines carrying SE-positive HLA-DR alleles displayed a higher rate of spontaneous NO production compared with SE-negative cells. L cell transfectants expressing SE-positive DR molecules on their surface also generated higher levels of NO. Tetrameric HLA-DR molecules containing a DRbeta-chain encoded by the SE-positive DRB1*0401 allele stimulated fibroblast cells to produce higher levels of NO compared with cells stimulated with a control HLA-DR tetramer. Multimeric hepatitis B core proteins engineered to express region 65-79 encoded by the DRB1*0401 allele, but not the same region encoded by the control allele DRB1*0402, stimulated NO production in fibroblasts. Similarly, synthetic 15-mer peptides corresponding to the region 65-79 encoded by SE-positive alleles triggered increased NO levels when incubated with class II major histocompatibility complex-negative cells. The signaling pathway was found to involve NO synthase activation, followed by increased production of cGMP. SE-triggered increased NO levels inhibited cytolytic elimination of target cells.

CONCLUSION

The SE can trigger NO-mediated signaling events in opposite cells, and may thereby contribute to RA pathogenesis.

HPRT mutations, TCR gene rearrangements, and HTLV-1 integration sites define in vivo T-cell clonal lineages

HPRT mutations in vivo in human T-lymphocytes are useful probes for mechanistic investigations. Molecular analyses of isolated mutants reveal their underlying mutational changes as well as the T-cell receptor (TCR) gene rearrangements present in the cells in question. The latter provide temporal reference points for other perturbations in the in vivo clones as well as evidence of clonal relationships among mutant isolates. Immunological studies and investigations of genomic instability have benefited from such analyses. A method is presented describing a T-cell lineage analysis in a patient with HTLV-1 infection. Lineage reconstruction of an in vivo proliferating HPRT mutant clone allows timing of the integration event to a postthymic differentiated cell prior to the occurrence of HPRT mutations.

Frequent HPRT mutations in paroxysmal nocturnal haemoglobinuria reflect T cell clonal expansion, not genomic instability

Paroxysmal nocturnal haemoglobinuria (PNH) results from acquired mutations in the PIG-A gene of an haematopoietic stem cell, leading to defective biosynthesis of glycosylphosphatidylinositol (GPI) anchors and deficient expression of GPI-anchored proteins on the surface of the cell's progeny. Some laboratory and clinical findings have suggested genomic instability to be intrinsic in PNH; this possibility has been supported by mutation analysis of hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene abnormalities. However, the HPRT assay examines lymphocytes in peripheral blood (PB), and T cells may be related to the pathophysiology of PNH. We analysed the molecular and functional features of HPRT mutants in PB mononuclear cells from eleven PNH patients. CD8 T cells predominated in these samples; approximately half of the CD8 cells lacked GPI-anchored protein expression, while only a small proportion of CD4 cells appeared to derive from the PNH clone. The HPRT mutant frequency (Mf) in T lymphocytes from PNH patients was significantly higher than in healthy controls. The majority of the mutant T lymphocyte clones were of CD4 phenotype, and they had phenotypically normal GPI-anchored protein expression. In PNH patients, the majority of HPRT mutant clones were contained within the Vbeta2 T cell receptor (TCR) subfamily, which was oligoclonal by complementarity-determining region three (CDR3) size analysis. Our results are more consistent with detection of uniform populations of expanded T cell clones, which presumably acquired HPRT mutations during antigen-driven cell proliferation, and not due to an increased Mf in PNH. HPRT mutant analysis does not support underlying genomic instability in PNH.

Microsatellite instability and suppressed DNA repair enzyme expression in rheumatoid arthritis

Reactive oxygen and nitrogen are produced by rheumatoid arthritis (RA) synovial tissue and can potentially induce mutations in key genes. Normally, this process is prevented by a DNA mismatch repair (MMR) system that maintains sequence fidelity during DNA replication. Key members of the MMR system include MutSalpha (hMSH2 and hMSH6) and MutSbeta (hMSH2 and hMSH3). To provide evidence of DNA damage in inflamed synovium, we analyzed synovial tissues for microsatellite instability (MSI). MSI was examined by PCR on genomic DNA of paired synovial tissue and peripheral blood cells of RA patients using specific primer sequences for five key microsatellites. Surprisingly, abundant MSI was observed in RA synovium compared with osteoarthritis tissue. Western blot analysis for the expression of MMR proteins demonstrated decreased hMSH6 and increased hMSH3 in RA synovium. To evaluate potential mechanisms of MMR regulation in arthritis, fibroblast-like synoviocytes (FLS) were isolated from synovial tissues and incubated with the NO donor S-nitroso-N-acetylpenicillamine. Western blot analysis demonstrated constitutive expression of hMSH2, 3, and 6 in RA and osteoarthritis FLS. When FLS were cultured with S-nitroso-N-acetylpenicillamine, the pattern of MMR expression in RA synovium was reproduced (high hMSH3, low hMSH6). Therefore, oxidative stress can relax the DNA MMR system in RA by suppressing hMSH6. Decreased hMSH6 can subsequently interfere with repair of single base mutations, which is the type observed in RA. We propose that oxidative stress not only creates DNA adducts that are potentially mutagenic, but also suppresses the mechanisms that limit the DNA damage.

Different patterns of bcl-6 and p53 gene mutations in tonsillar B cells indicate separate mutational mechanisms

Mutations within the 5'-non-coding region of the bcl-6 gene can occur in lymphomas that originate from germinal centers (GCs), as well as in normal memory and GC B cells. Mutations in the p53 gene occur in 50% of human cancers. Since both bcl-6 and p53 can be mutated in certain circumstances, we investigated the accumulation of mutations in these genes in individual tonsillar B and T cells to determine whether the mutations exhibited a pattern anticipated from the B-cell hypermutation machinery. In tonsillar GC B cells, the overall mutational frequencies in the 5'-non-coding region of the bcl-6 gene was 0.85 x 10(-3)/bp. In contrast, there were no mutations in a region 2.8 kb downstream of the promoter. RGYW (purine, guanine, pyrimidine, A/T) targeting and a significantly lower mutational frequency in nai;ve B and GC founder B cells compared with GC B cells suggested that a similar mutator mechanism was active on Ig genes and this non-Ig gene. The mutational frequency in the exon-7-region of p53 was similar in the GC, memory and nai;ve B-cell subsets (1.02 x 10(-3) to 1.25 x 10(-3)/bp). RGYW/WRCY motifs were not targeted preferentially in the p53 gene. Moreover, a comparable mutational frequency of p53 was noted in tonsillar B and T cells. Hence, mutations in p53 do not appear to be the result of the B-cell hypermutational mechanism.

Regional analysis of p53 mutations in rheumatoid arthritis synovium

The p53 tumor suppressor protein plays a central role in cell cycle regulation, DNA repair, and apoptosis. Recent studies indicate that DNA damage and somatic mutations in the p53 gene can occur because of genotoxic stress in many tissues, including the skin, colon, and synovium. Although somatic mutations in the p53 gene have been demonstrated in rheumatoid arthritis (RA) synovial tissue and synoviocytes, no information is available on the location or extent of p53 mutations. Using microdissected RA synovial tissue sections, we observed abundant p53 transition mutations, which are characteristic DNA damage caused by oxidative stress. p53 mutations, as well as p53 mRNA expression, were located mainly in the synovial intimal lining rather than the sublining (P < 0.01). Clusters of p53 mutant subclones were observed in some microdissected regions, suggesting oligoclonal expansion. Because IL-6 gene expression is regulated by wild-type p53, IL-6 mRNA expression in microdissected tissues was quantified by using real-time PCR. The regions with high rates of p53 mutations contained significantly greater amounts of IL-6 mRNA compared with the low mutation samples (P < 0.02). The microdissection findings suggest that p53 mutations are induced in RA synovial tissues by inflammatory oxidative stress. This process, as in sun-exposed skin and inflamed colonic epithelium, provides some of the mutant clones with a selective growth advantage. A relatively low percentage of cells containing p53 mutations can potentially affect neighboring cells and enhance inflammation through the elaboration of proinflammatory cytokines.

The genetics of the target tissue in rheumatoid arthritis

The genetic mechanisms that are complementary in predisposing and then establishing disease are yet to be fully elucidated. During a lifetime, the genetic composition of the host is not only hereditary but undergoes rearrangements, integrations, and more subtle single-base pair alterations. These changes can be inconsequential or lead to aberrant and deleterious pathologic changes. In a complex multifactorial disease such as RA, the relative roles of the dynamic versus germline elements of the disease have yet to be fully determined. Further studies of large populations are likely to segregate out factors affecting specific ethnic, clinical, and genetic subgroups.

In vivo mutant frequency of thioguanine-resistant T-cells in the peripheral blood and lymph nodes of melanoma patients

T-cell activation by malignant melanoma would be anticipated to stimulate T-cell proliferation, which in turn has been associated with increasing the likelihood of somatic gene mutation. The purpose of this study was to test the hypothesis that in vivo hypoxanthine guanine phosphoribosyltransferase (hprt) mutant frequencies (MFs) are increased in peripheral blood T-cells from melanoma patients compared to normal controls. Assays were made of 48 peripheral blood samples from melanoma patients with stage 3 (13 patients) and stage 4 (35 patients) disease, 38 normal controls, and of nine tumor bearing lymph nodes. The mean hprt log(10)(MF) in patient peripheral blood was -4.77 (geometric mean hprt MF=17.0x10(-6)) compared to a mean hprt log(10)(MF) of -4.87 (geometric mean hprt MF=13.5x10(-6)) in controls. Although modest, this difference is statistically significant both by t-test (P=0.049) and after adjustment for covariates of age, gender, and cigarette smoking by regression analysis (P=0.001). Among the melanoma patients, the mean log(10)(MF) for the 17 patients who had received potentially genotoxic therapies was not significantly different from the mean log(10)(MF) for the 31 patients not receiving such therapies. The hprt MFs in the nine tumor bearing nodes were compared with MFs in peripheral blood from the same patients and revealed a non-significant (P=0.07) trend for increasing MFs in blood. Furthermore, analyses of T-cell receptor gene rearrangement patterns revealed hprt mutants originating from the same in vivo clone in both peripheral blood and a tumor-bearing node. The finding of elevated hprt MFs not entirely explained by genotoxic therapies in patients compared to controls can be explained either by hypermutability or in vivo T-cell activation. The similar MFs in peripheral blood and tumor bearing lymph nodes, as well as the finding of mutant representatives of the same in vivo T-cell clone in both locations, support monitoring peripheral blood to detect events in the nodes. If in vivo proliferation accounts for the current findings, the hprt deficient (hprt-) mutant fraction in blood may be enriched for T-cells that mediate the host immune response against malignant melanoma. Further studies will characterize the functional reactivity of hprt mutant isolates against melanoma-related antigens.

Pathogenesis of rheumatoid arthritis: the role of synoviocytes

Considering the characteristics of RA synovial tissues such as marked proliferation and invasion to adjacent tissues, comparisons with transformed or neoplastic tissue are natural. RA synovial tissues or cells are not truly malignant, but they have many features of transformation, denoted as "partial transformation" in this article. These features include anchorage-independent growth, loss of contact inhibition, oncogene activation, monoclonal or oligoclonal expansion, detectable telomerase activity, and somatic gene mutations. Although it is not possible to conclude whether most of these cells are permanently changed in association with some genetic alterations or are passively changed by virtue of environmental factors (i.e., cytokine-mediated imprinting), the presence of p53 mutations in RA synovial tissues is especially persuasive. A number of transcription factors play a critical role in the activation, differentiation, and proliferation of RA synovial cells. In particular, the roles of AP-1, MAPKs, and NF-kappa B have been investigated carefully because of their ability to regulate numerous inflammation-related genes. These transcription factors also control expression and activation of matrix-degrading enzymes, including MMPs, aggrecanase, and cysteine proteases, which are the primary enzymes responsible for joint destruction. Elucidation of gene mutations and detailed signal transduction pathways that are specific to RA as well as mechanisms of action of matrix-degrading enzymes may lead to development of a novel therapy for RA. Careful mapping of cytokine networks a decade ago led to groundbreaking advances in therapy. Similarly, methodical evaluation and prioritization of intracellular targets might provide the basis for therapeutic interventions.

Nitric oxide donors induce large-scale deletion mutations in human lymphoblastoid cells: implications for mutations in T-lymphocytes from arthritis patients

Rheumatoid arthritis (RA) is an inflammatory disease in which high levels of reactive nitrogen oxygen species (RNOS) may be present in the affected joints. RNOS are known to produce small-scale mutational events (transitions, transversions, small insertions, and small deletions) but the ability of these compounds to cause deletion of large segments of genomic DNA has not been previously determined. To address this question, a human lymphoblastoid cell line (WIL2-NS) was exposed to nitric oxide (NO)-donating drugs and hypoxanthine phosphoribosyltransferase (hprt)-negative clones were selected and analyzed by multiplex-PCR. Large-scale deletions accounted for 60-80% of hprt mutations arising in drug-treated cultures compared to 12% in untreated cultures (P-values of 0.006 and 0.0001, respectively, in two experiments). Deletion mutations in untreated cultures affected exon 9, whereas 75% of drug-induced deletion mutations affected exons 2, 3, and 9, and the remainder were very large, ranging from 26 to 1200 kbp. To compare this spectrum of NO-induced mutations in a lymphoblastoid line to that arising in vivo in arthritis patients, T-cells from RA patients, osteoarthritis (OA) patients, and controls were cloned and similarly analyzed. We previously showed that the overall frequency of Hprt mutant clones from patients is appreciably elevated compared to that of control subjects. Large-scale hprt deletions (0.5 to >26 kb) were detected in mutant T-cell clones from both RA and OA patients and also from control subjects. A total of 54 mutant clones from 16 RA patients and 19 mutant clones from 6 OA patients were studied. Of these, 6 clones (from 3 RA and 1 OA patient) had suffered large-scale deletions. A total of 9 control subjects were studied and 62 mutant clones were obtained. Of these, 19 had suffered large-scale deletions, arising in 7 of 9 control subjects. In conclusion, (1) RNOS are capable of inducing large-scale deletion mutations in a human lymphoblastoid cell line and (2) large-scale deletion mutations were found in 10-30% of T-cell clones from RA and OA patients and controls, which we hypothesize may be induced by RNOS.

Rheumatoid arthritis and p53: how oxidative stress might alter the course of inflammatory diseases

Oxidative stress at sites of chronic inflammation can cause permanent genetic changes. The development of mutations in the p53 tumor suppressor gene and other key regulatory genes could help convert inflammation into chronic disease in rheumatoid arthritis and other inflammatory disorders.

Neutrophils, nitric oxide synthase, and mutations in the mutatect murine tumor model

Mutatect MN-11 is a tumor line that can be grown subcutaneously in syngeneic C57BL/6 mice. The frequency of spontaneously arising mutants at the hypoxanthine phosphoribosyltransferase (Hprt) locus was observed to be elevated as a result of in vivo growth. The objective of the present study was to identify factors in the tumor microenvironment that might explain this increase in mutant frequency (MF). When tumors were examined histologically, neutrophils were found to be the predominant infiltrating cell type. Quantitative estimates of the number of neutrophils and MF of tumors in different animals revealed a statistically significant correlation (r = 0.63, P < 0.0001). Immunohistochemical analysis for inducible nitric oxide synthase (iNOS) demonstrated its presence, mainly in neutrophils. Biochemical analysis of tumor homogenates for nitric oxide synthase (NOS) activity indicated a statistically significant correlation with MF (r = 0.77, P < 0.0001). Nitrotyrosine was detected throughout the tumor immunohistochemically; both cytoplasmic and nuclear staining was seen. To increase the number of infiltrating neutrophils, tumors were injected with chemoattractant interleukin-8 and prostaglandin E2. This produced a statistically significant increase in neutrophil content (P = 0.005) and MF (P = 0.0002). As in control MN-11 tumors, neutrophil content and MF were strongly correlated (r = 0.63, P = 0. 003). Because neutrophils are a potential source of genotoxic reactive oxygen and/or nitrogen species, our results support the notion that these tumor-infiltrating cells may be mutagenic and contribute to the burden of genetic abnormalities associated with tumor progression.

Elimination of non-viable 6-thioguanine-sensitive T cells from viable T cells prior to PCR analysis

The study of T cell clones at the genomic level is expanding our understanding of their role in diseases such as rheumatoid arthritis (RA) and multiple sclerosis (MS). We have been carrying out genotypic analysis by PCR of hypoxanthine phosphoribosyltransferase (hprt) mutations in these cells. Mutant T cells in the population can be cloned on the basis of their resistance to the cytotoxic drug, 6-thioguanine-(6-TG). A difficulty is that the majority of primary human T cells are capable of only limited growth ex vivo, even in the presence of 'feeder' cells. PCR analysis of DNA from such clones is made difficult by the limited number of viable mutant (drug-resistant) T cells and the large number of dead (drug-sensitive) mononuclear cells and feeder cells. DNA from the 'dead' cells remains sufficiently intact for many weeks in culture and can represent a significant source of background in PCR analysis. Here we describe a method employing hypotonic shock and micrococcal nuclease that reliably eliminates non-viable 6-TG-sensitive cells, allowing the study of the hprt gene in < 200 T cells by PCR.