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Polymorphisms in Cytokine and Cellular Adhesion Molecule Genes and Susceptibility to Hematotoxicity among Workers Exposed to Benzene

¹ Division of Cancer Epidemiology and Genetics and ² Center for Cancer Research, National Cancer Institute, NIH, Department of Health and Human Services, Bethesda, Maryland; ³ School of Public Health, University of California, Berkeley, California; ⁴ Chinese Center for Disease Control and Prevention, Beijing, China; ⁵ School of Public Health, University of North Carolina, Chapel Hill, North Carolina; and ⁶ New York Blood Center, Clinical Services, White Plains, New York

Requests for reprints: Qing Lan, Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, MSC 7240, 6120 Executive Boulevard, EPS 8109, Bethesda, MD 20892-7240. Phone: 301-435-4706; Fax: 301-402-1819; E-mail: qingl{at}mail.nih.gov.

	Abstract

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Benzene is a recognized hematotoxin and leukemogen but its mechanism of action and the role of genetic susceptibility are still unclear. Cytokines, chemokines, and cellular adhesion molecules are soluble proteins that play an important regulatory role in hematopoiesis. We therefore hypothesized that variation in these genes could influence benzene-induced hematotoxicity. We analyzed common, well-studied single-nucleotide polymorphisms (SNPs) in 20 candidate genes drawn from these pathways in a study of 250 workers exposed to benzene and 140 unexposed controls in China. After accounting for multiple comparisons, SNPs in five genes were associated with a statistically significant decrease in total WBC counts among exposed workers [IL-1A (–889C>T), IL-4 (–1098T>G), IL-10 (–819T>C), IL-12A (8685G>A), and VCAM1 (–1591T>C)], and one SNP [CSF3 (Ex4–165C>T)] was associated with an increase in WBC counts. The adhesion molecule VCAM1 variant was particularly noteworthy as it was associated with a decrease in B cells, natural killer cells, CD4⁺ T cells, and monocytes. Further, VCAM1 (–1591T>C) and CSF3 (Ex4–165C>T) were associated, respectively, with decreased (P = 0.041) and increased (P = 0.076) CFU-GEMM progenitor cell colony formation in 29 benzene-exposed workers. This is the first report to provide evidence that SNPs in genes that regulate hematopoiesis influence benzene-induced hematotoxicity.

	Introduction

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Chronic benzene exposure causes a range of hematologic disorders, including hematotoxicity, myelodysplatic syndrome, leukemia, and possibly non-Hodgkin lymphoma (1–3). Although there are ongoing concerns about its health effects (4), benzene continues to be used as a solvent in some countries, with several million workers exposed worldwide (4), and is a component of cigarette smoke, gasoline, crude oil, and automobile emissions (2). Several mechanisms have been suggested to account for benzene-induced hematotoxicity, including (a) direct toxicity to hematopoietic progenitor cells by genotoxic and cytotoxic metabolites of benzene (5–8) and (b) poisoning of the bone marrow stromal microenvironment (9, 10), whereby shifts in regulatory molecules produced by marrow cells could disrupt normal hematopoiesis (11–14).

Interindividual variation to benzene-induced hematotoxicity has been observed in occupational studies, in which highly disparate responses have been noted among workers with similar benzene exposure (15, 16), suggesting a role for individual genetic susceptibility. The first reports to evaluate mechanisms of genetic susceptibility for benzene hematotoxicity identified genetic variations in enzymes responsible for benzene metabolism (e.g., CYP2E1, MPO, NQO1; refs. 3, 16). We hypothesized that another important source of susceptibility to benzene-induced hematotoxicity would be variation in selected cytokine, chemokine, and cellular adhesion genes because mounting evidence suggests that control of hematopoietic cell growth and differentiation, both during healthy conditions and in response to stress, is partly regulated by the cytokine, chemokine, and adhesion molecule networks (17, 18).

We recently reported the presence of hematotoxicity in Chinese workers exposed to low levels of benzene (<1 ppm, the U.S. occupational standard; ref. 3). Exposure to benzene and other solvents was extensively evaluated, and detailed information was collected on potential confounders including lifestyle, medication, and medical history. Here, we report the influence of single-nucleotide polymorphisms (SNPs) in hematopoiesis regulatory genes on benzene-induced hematotoxicity.

	Materials and Methods

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Study population, exposure assessment, and biological sample collection. The study population has previously been described (3, 19). In brief, we studied 250 benzene-exposed shoe workers in China and 140 unexposed controls, frequency matched to the benzene-exposed workers by age and sex. The study was approved by the Institutional Review Boards of the U.S. National Cancer Institute and the China Center for Disease Control. Written informed consent was provided by all study participants. We carried out a comprehensive workplace evaluation of exposure to benzene and toluene, as well as to other organic solvents (3, 19). About 40% of the workers were on average exposed to <1 ppm benzene in the month before their blood sample was collected.

Interviews were carried out and blood samples were collected from 88 workers in June 2000 and from the remaining workers in May and June 2001 (28 subjects enrolled in the first year had repeat samples in the second year). A detailed questionnaire was administered requesting information on lifetime occupational and environmental exposures, lifestyle, medical history, and other potential confounding factors. Each subject also had a brief physical exam (3, 19) and provided a 29 mL blood sample. Complete blood cell counts and differentials were analyzed by a Beckman-Coulter T540 blood counter. The major lymphocyte subsets were measured by a Becton Dickinson FACSCalibur flow cytometer (software: SimulSET v3.1; refs. 3, 19). Colony-forming unit progenitor cells were cultured from peripheral blood from 29 workers selected for a wide range of measured benzene exposures (3).

Genotyping. We selected 40 SNPs in 20 genes coding for cytokines, chemokines, and adhesion molecules that play a role in hematopoiesis, based on the following criteria: minor allele frequencies of >5%, evidence of functionality in experimental or human studies, known association with disease, or to facilitate haplotype analysis (Table 1). Genotyping was done on an ABI 7900HT detection system using TaqMan end point reads as described on the website (20).⁷ Missing genotype data resulted from nonspecific failure of samples to amplify or to yield unambiguous genotype calls. Blind replicate samples were randomly interspersed throughout the study sample plates and showed intrasubject concordance rates of >99% for all assays.

We tested the influence of each SNP on total WBC counts separately in workers exposed to benzene and among unexposed controls. Total WBC count was the key end point in this study because a decreased WBC count (under 4,000 cells/µL) measured repeatedly is the primary component of a diagnosis of benzene poisoning in China, which we have previously linked to risk for developing hematologic malignancies and related disorders among workers exposed to benzene (16).

For analysis of gene variants, the most prevalent homozygous genotype was considered the reference group. Data for minor homozygotes and heterozygotes were combined in the analysis if the former contained fewer than five subjects. Cell counts are presented in tables as unadjusted means (± SD). Linear regression was used to analyze the relationship between each genotype and the natural log (ln) of the total WBC count, adjusting for age (continuous variable), sex, current cigarette smoking status (yes/no), current alcohol consumption (yes/no), recent infections (yes/no), and body mass index (BMI), and in exposed workers and additionally for the ln mean air benzene exposure and ln mean air toluene exposure in the month before phlebotomy (3). The selection of potential confounding factors was based on the literature and associations observed in the current study population (3). Further adjustment for variants in MPO and NQO1, which we have previously reported influence WBC counts among exposed workers in this study (3), did not affect the associations reported here. Tests for gene-dosage effect (i.e., trend) were conducted by treating genotype as a continuous variable (0, 1, and 2 for the most prevalent homozygous, heterozygous, and variant homozygous genotypes, respectively). Gene-environment interactions were tested by adding a product term between the genotype (variant homozygous and heterozygous carriers combined versus most prevalent homozygous carriers) and benzene exposure (yes/no) into each model. Data from the 28 benzene-exposed workers studied in both years are treated independently by using generalized estimating equations to adjust for potential correlation between the repeated measurements (21). Results were negligibly affected when data from only the first or second year of study were used for these 28 subjects.

We controlled for multiple hypothesis testing by calculating the false discovery rate, using the Benjamini-Hochberg method (22), for results from the initial screening of the effect of each SNP on the total WBC count, the primary end point in our study. The false discovery rate is defined as the expected ratio of erroneous rejections of the null hypothesis to the total number of rejected hypotheses; we used a false discovery rate of 0.05 to report associations for which the proportion of expected false positives was <5%. False discovery rate–adjusted P values were calculated for change in WBC counts for homozygous carriers of the rare versus common allele, as this provides the greatest potential contrast in effects across genotypes.

Those SNPs with false discovery rate–adjusted P values of <0.05 that also showed significant gene-dosage effects (if testable) among workers exposed to benzene were further tested for their influence on specific WBC types, colony-forming unit granulocyte-macrophage (CFU-GM) progenitor cells, and colony-forming unit granulocyte-erythroid-macrophage-megakaryocyte (CFU-GEMM) progenitor cells. Negative binomial regression was used to evaluate each SNP association with CFU-GM colony counts, and logistic regression was used to test the association with CFU-GEMM colonies, as there were multiple subjects with no measurable colonies (3). The progenitor cell models were adjusted for only age, sex, and ln benzene to avoid overparameterizing a model with 29 observations, as other potential confounders were not significant. All P values presented are two sided and all analyses were carried out using SAS version 8.02 software (SAS Institute, Cary, NC).

When possible, a preliminary analysis of haplotype block structure was examined with HaploView⁸ using the four gamete rule with a minimum frequency of 0.005 for the fourth gamete. Haplotypes were estimated using the expectation-maximization algorithm (23). The association between blood cell counts and estimated haplotypes was assessed separately for controls and exposed subjects, adjusting for potential confounders using the HaploStats program (24) in R (Version 2.0.1; ref. 25).

	Results

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Table 2 presents demographic characteristics, benzene exposure, and peripheral blood cell counts by benzene exposure status (i.e., controls versus exposed workers). The majority of the controls and benzene-exposed subjects were female and relatively young. The subjects in the benzene-exposed and nonexposed groups were comparable in terms of alcohol use, recent infection, smoking status, and BMI. The mean (SD) benzene air exposure was 5.44 (12.1) ppm in the exposed group, based on measurements made in the month before phlebotomy. The total WBC count, most WBC subtypes, and the platelet count were significantly decreased in benzene-exposed workers compared with controls. Natural killer (NK) cell counts and hemoglobin concentration were significantly decreased only among the most highly exposed workers, as previously reported, and CD8⁺ T cells did not differ between groups at any level of exposure (3).

We conducted further analyses to evaluate the influence of the six SNPs shown in Table 3 on specific WBC populations in benzene-exposed workers (Table 4). The effect of SNPs in IL-1A, IL-10, and CSF3 was limited to granulocyte counts, with decreased cell counts observed for IL-1A and IL-10 and increased cell counts for CSF3. The IL-4 promoter SNP was significantly associated with decreased granulocyte and total lymphocyte counts; and the IL-12A variant was associated with decreased granulocytes, total lymphocyte count, and CD4⁺ and CD8⁺ T-cell subsets. Interestingly, the VCAM1 SNP displayed the broadest effect on WBC subtypes, with significant decreases for total lymphocyte count, CD4⁺ T cells, B cells, NK cells, and monocytes, and a borderline significant decrease for granulocytes (Table 4).

Because a number of SNPs in Table 4 influenced several mature WBC subtypes (e.g., granulocytes, CD4⁺ T cells, B cells, and monocytes), we carried out an exploratory analysis of the effect of each SNP on CFU-GM and CFU-GEMM progenitor cell counts, which were available from 29 workers exposed to benzene (the IL-1A variant could not be evaluated as there was only one carrier in this group). There were no significant effects observed for any SNP on CFU-GM progenitor cells. The VCAM1 variant was, however, significantly associated with a decrease in CFU-GEMM counts (Fig. 1A(i)) and the CSF3 SNP showed a borderline significant increase with CFU-GEMM counts (Fig. 1B(i)), consistent with the direction of their effect on total WBC counts (Fig. 1A(ii) and B(ii); Table 3).

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Effect of SNPs in VCAM1 and CSF3 on CFU-GEMM and peripheral WBC counts in workers exposed to benzene (columns, mean; bars, SE). A, i, VCAM1 (–1591T>C) and CFU-GEMM colony count; ii, VCAM1 (–1591T>C) and WBC count. B, i, CSF3 (Ex4–165C>T) and CFU-GEMM colony count; ii, CSF3 (Ex4–165C>T) and WBC count. Unconditional logistic regression was used to test effects on CFU-GEMM, categorizing subjects into 0 or more than 0 colonies. A, i, 79% and 30% of subjects had >0 colonies among TT and TC genotypes, respectively. B, i, 43%, 61%, and 100% of subjects had >0 colonies among CC, CT, and TT genotypes, respectively. Linear regression was used for trend test with each genotype and WBC count shown in A(ii) and B(ii).

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
We studied the effect of 40 SNPs in 20 cytokine, chemokine, and cellular adhesion molecule genes on peripheral WBC counts among 250 workers exposed to benzene and 140 unexposed controls. After carrying out a series of analyses that accounted for multiple comparisons, we observed robust findings for common SNPs in five genes (four cytokines and one adhesion molecule) that were associated with a decrease in total WBC counts among exposed workers (Table 3). On further analysis, the IL-1A and IL-10 variants were significantly associated with only granulocytes, the IL-4 promoter SNP was associated with a decline in both granulocytes and total lymphocytes, and the IL-12A and VCAM1 SNPs were associated with declines in three and four WBC subtypes, respectively (Table 4). Interestingly, the VCAM1 SNP was also associated with a significant decline in CFU-GEMM cells in a subgroup of 29 exposed workers (Fig. 1). In contrast, we found that one SNP in CSF3 was associated with a significant increase in granulocytes (Table 3) and a borderline significant increase in CFU-GEMM colony counts (Fig. 1).

Benzene is metabolized to toxic compounds, which are known to cause bone marrow suppression, perhaps by complimentary mechanisms. Benzene can directly damage hematopoietic progenitor cells (5–8, 26), which could lead to apoptosis or decreased responsiveness to cytokines and cellular adhesion molecules. Alternatively, benzene toxicity to stromal cells or mature blood cells could disrupt the regulation of hematopoiesis, including hematopoietic commitment, maturation, or mobilization, through the network of cytokines, chemokines, and adhesion molecules (11–14, 27). Accordingly, hematotoxic effects could be enhanced among individuals exposed to benzene who have genetic variants that alter key pathways that regulate hematopoiesis.

There is mounting evidence that benzene may alter the gene expression, production, or processing of several cytokines in vitro or in vivo. Both benzene and its metabolite hydroquinone were found to interact with signaling pathways regulated by granulocyte colony-stimulating factor (27). Benzoquinone and hydroquinone were shown to alter interleukin (IL)-1 processing, possibly by decreasing the content of the IL-1 processing enzyme calpain (11, 13, 28). Hydroquinone was reported to interrupt B-cell lymphopoiesis, possibly by inhibiting production of IL-4 by fibroblastic stromal cells (29), and was found to enhance IL-4 mRNA expression and IL-4 production in CD4⁺ T cells (30). Further, a recent report from our study population showed a highly significant increase in IL-4R mRNA expression in peripheral mononuclear cells from benzene-exposed workers (31). The influence of benzene on the production and function of IL-10, IL-12, or VCAM1, and how benzene might alter stem, progenitor, or stromal cell responses to these compounds, is not known.

Published data support the importance of these genes in hematopoiesis; for instance, IL-1, IL-4, IL-10, and IL-12 have each been implicated in myelopoiesis and lymphopoiesis (29, 32–34). IL-12 and IL-4 play a role in the proliferation of T cells (34, 35) and VCAM1 has been shown to be critical for successful hematopoiesis in the bone marrow for cells of both myeloid and lymphoid lineage (17, 36, 37). It is also notable that several of our most significant findings were in genes that regulate the Th1-Th2 lymphocyte balance. In particular, we observed that variation in cytokines IL-4, IL-10, and IL-12A was each associated with decreased WBC. This raises the possibility that a shift in the balance of Th1-Th2 could have important consequences for the challenge of benzene to granulopoiesis and lymphopoiesis.

For three of the genes, IL-1A, IL-4, and IL-10, the variants studied have been reported to have functional consequences, either directly or as part of a haplotype. For instance, the IL-1A (–889C>T) is in the 5' untranslated region, has been shown to produce a higher amount of IL-1A mRNA (38), and has been associated with autoimmune, degenerative, and infectious diseases (39, 40). The IL-4 promoter SNPs and haplotypes are particularly interesting because of emerging studies that indicate that variation in the expression of this gene could affect a range of diseases such as severity of infection with respiratory syncytial virus in young children, asthma, atopy, fungal infection with Candida albicans in leukemia patients, and inflammatory bowel disease (41–44); moreover, this same promoter SNP has been shown to increase reporter gene expression in vitro (41, 42, 45). Lastly, proximal promoter IL-10 haplotypes have been shown to alter IL-10 secretion (46–48) and a specific haplotype containing IL-10 (–819T) has been associated with elevated IL-10 mRNA levels (47). IL-10 promoter haplotypes have been associated with progression of HIV infection, autoimmune diseases such as asthma, lupus erythematosus, graft-versus-host disease following marrow transplantation, and Alzheimer's disease (49–52).

We detected associations between WBC counts and variants in three additional genes, VCAM1, CSF3, and IL-12A, but the specific function of these alleles is unknown. Recent reports found that SNPs in the VCAM1 gene, including the –1591C allele, were associated with increased risk of stroke (53, 54), suggesting that this variant, or a SNP in linkage disequilibrium, could be functional. The CSF3 (Ex4–165C>T) and IL-12A (8685G>A) variants are in 3' untranslated regions, which could alter gene translation by several processes including ribosome binding, initiation, and elongation (55), but additional work is needed to determine their functionality.

In summary, this is the first report to show that common SNPs in cytokine genes and VCAM1 could be associated with hematotoxicity in workers exposed to benzene. Selected variants seemed to influence only granulocytes, whereas others altered cell types of both myeloid and lymphoid lineage, suggesting effects that could extend to earlier progenitor and possibly stem cells. Follow-up studies will require analysis with more comprehensive haplotypes containing the SNPs profiled in this study; in parallel, functional analysis should proceed in the laboratory to advance the identification of causal variants in benzene-induced hematotoxicity and to define specific mechanisms that explain their effects on peripheral WBC counts in the presence of benzene. At the same time, results of this study, although highly statistically significant, need to be confirmed in other populations exposed to benzene and extended to studies of benzene-related hematologic neoplasms and related disorders (2). Finally, our findings suggest that it may also be worthwhile to explore how these and related SNPs affect hematopoiesis and risk of hematologic disorders in people exposed to other environmental or pharmacologic hematotoxins and leukemogens.

	Acknowledgments

 
Grant support: Intramural Research Program of the NIH, National Cancer Institute; and NIH grants RO1ES06721, P42ES04705, and P30ES01896 (M.T. Smith), and P42ES05948 and P30ES10126 (S.M. Rappaport).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

We thank Dr. Nilanjan Chatterjee for the false discovery rate calculation and the participants for taking part in this study.

	Footnotes

 
Note: M.T. Smith has received consulting and expert testimony fees from law firms representing both plantiffs and defendants in cases involving exposure to benzene. G. Li has received funds from the American Petroleum Institute for consulting on benzene-related health research.

⁷ http://snp500cancer.nci.nih.gov

⁸ http://www.broad.mit.edu/personal/jcbarret/haploview/

Received 4/26/05. Revised 8/ 8/05. Accepted 8/ 9/05.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

1. Hayes RB, Yin SN, Dosemeci M, et al. Benzene and the dose-related incidence of hematologic neoplasms in China. Chinese Academy of Preventive Medicine—National Cancer Institute Benzene Study Group. J Natl Cancer Inst 1997;89:1065–71.[Abstract/Free Full Text]
2. Gist GL, Burg JR. Benzene—a review of the literature from a health effects perspective. Toxicol Ind Health 1997;13:661–714.[Abstract/Free Full Text]
3. Lan Q, Zhang L, Li G, et al. Hematotoxicity in workers exposed to low levels of benzene. Science 2004;306:1774–6.[Abstract/Free Full Text]
4. Ward E. Overview of preventable industrial causes of occupational cancer. Environ Health Perspect 1995;103 Suppl 8:197–203.
5. Chen H, Rupa DS, Tomar R, Eastmond DA. Chromosomal loss and breakage in mouse bone marrow and spleen cells exposed to benzene in vivo. Cancer Res 1994;54:3533–9.[Abstract/Free Full Text]
6. Irons RD, Neptun DA. Effects of the principal hydroxy-metabolites of benzene on microtubule polymerization. Arch Toxicol 1980;45:297–305.[CrossRef][Medline]
7. Smith MT, Zhang L, Jeng M, et al. Hydroquinone, a benzene metabolite, increases the level of aneusomy of chromosomes 7 and 8 in human CD34-positive blood progenitor cells. Carcinogenesis 2000;21:1485–90.[Abstract/Free Full Text]
8. Zhang L, Eastmond DA, Smith MT. The nature of chromosomal aberrations detected in humans exposed to benzene. Crit Rev Toxicol 2002;32:1–42.[CrossRef][Medline]
9. Garnett HM, Cronkite EP, Drew RT. Effect of in vivo exposure to benzene on the characteristics of bone marrow adherent cells. Leuk Res 1983;7:803–10.[Medline]
10. Thomas DJ, Sadler A, Subrahmanyam VV, et al. Bone marrow stromal cell bioactivation and detoxification of the benzene metabolite hydroquinone: comparison of macrophages and fibroblastoid cells. Mol Pharmacol 1990;37:255–62.[Abstract]
11. Kalf GF, Renz JF, Niculescu R. p-Benzoquinone, a reactive metabolite of benzene, prevents the processing of pre-interleukins 1 and 1ß to active cytokines by inhibition of the processing enzymes, calpain, and interleukin-1ß converting enzyme. Environ Health Perspect 1996;104 Suppl 6:1251–6.
12. King AG, Landreth KS, Wierda D. Bone marrow stromal cell regulation of B-lymphopoiesis. II. Mechanisms of hydroquinone inhibition of pre-B cell maturation. J Pharmacol Exp Ther 1989;250:582–90.[Abstract/Free Full Text]
13. Miller AC, Schattenberg DG, Malkinson AM, Ross D. Decreased content of the IL1 processing enzyme calpain in murine bone marrow-derived macrophages after treatment with the benzene metabolite hydroquinone. Toxicol Lett 1994;74:177–84.[CrossRef][Medline]
14. Ross D, Siegel D, Schattenberg DG, Sun XM, Moran JL. Cell-specific activation and detoxification of benzene metabolites in mouse and human bone marrow: identification of target cells and a potential role for modulation of apoptosis in benzene toxicity. Environ Health Perspect 1996;104 Suppl 6:1177–82.
15. Goldstein BD. Benzene toxicity: a critical evaluation: introduction. J Toxicol Environ Health Suppl 1977;2:1–4.[Medline]
16. Rothman N, Smith MT, Hayes RB, et al. Benzene poisoning, a risk factor for hematological malignancy, is associated with the NQO1 609CT mutation and rapid fractional excretion of chlorzoxazone. Cancer Res 1997;57:2839–42.[Abstract/Free Full Text]
17. Hall BM, Gibson LF. Regulation of lymphoid and myeloid leukemic cell survival: role of stromal cell adhesion molecules. Leuk Lymphoma 2004;45:35–48.[CrossRef][Medline]
18. Zhu J, Emerson SG. Hematopoietic cytokines, transcription factors and lineage commitment. Oncogene 2002;21:3295–313.[CrossRef][Medline]
19. Vermeulen R, Li G, Lan Q, et al. Detailed exposure assessment for a molecular epidemiology study of benzene in two shoe factories in China. Ann Occup Hyg 2004;48:105–16.[Abstract/Free Full Text]
20. Packer BR, Yeager M, Staats B, et al. SNP500Cancer: a public resource for sequence validation and assay development for genetic variation in candidate genes. Nucleic Acids Res 2004;32 (Database issue):D528–32.[Abstract/Free Full Text]
21. Zeger SL, Liang KY. Longitudinal data analysis for discrete and continuous outcomes. Biometrics 1986;42:121–30.[CrossRef][Medline]
22. Benjamini Y, Hochberg Y. Controlling the false discovery rate: a practical and powerful approach to multiple testing. J R Stat Soc B 1995;57:289–300.
23. Excoffier L, Slatkin M. Maximum-likelihood estimation of molecular haplotype frequencies in a diploid population. Mol Biol Evol 1995;12:921–7.[Abstract]
24. Schaid DJ, Rowland CM, Tines DE, Jacobson RM, Poland GA. Score tests for association between traits and haplotypes when linkage phase is ambiguous. Am J Hum Genet 2002;70:425–34.[CrossRef][Medline]
25. R Development Core Team. R: A language and environment for statistical computing. R Foundation for Statistical Computing. 2004.
26. Stillman WS, Varella-Garcia M, Irons RD. The benzene metabolite, hydroquinone, selectively induces 5q31- and -7 in human CD34+. Exp Hematol 2000;28:169–76.[CrossRef][Medline]
27. Kalf GF. Utility of a mouse model for studying the effects of benzene on the myeloid lineage: effects of hydroquinone on a model myeloid system. J Toxicol Environ Health A 2000;61:399–411.[Medline]
28. Renz JF, Kalf GF. Role for interleukin-1 (IL-1) in benzene-induced hematotoxicity: inhibition of conversion of pre-IL-1 to mature cytokine in murine macrophages by hydroquinone and prevention of benzene-induced hematotoxicity in mice by IL-1. Blood 1991;78:938–44.[Abstract/Free Full Text]
29. King AG, Wierda D, Landreth KS. Bone marrow stromal cell regulation of B-lymphopoiesis. I. The role of macrophages, IL-1, and IL-4 in pre-B cell maturation. J Immunol 1988;141:2016–26.[Abstract]
30. Lee MH, Chung SW, Kang BY, Kim KM, Kim TS. Hydroquinone, a reactive metabolite of benzene, enhances interleukin-4 production in CD4+ T cells and increases immunoglobulin E levels in antigen-primed mice. Immunology 2002;106:496–502.[CrossRef][Medline]
31. Forrest MS, Lan Q, Hubbard AE, et al. Discovery of novel biomarkers by microarray analysis of peripheral blood mononuclear cell gene expression in benzene-exposed workers. Environ Health Perspect 2005;113:801–7.[Medline]
32. Snoeck HW, Lardon F, Van Bockstaele DR, Peetermans ME. Effects of interleukin-4 (IL4) on myelopoiesis: studies on highly purified CD34+ hematopoietic progenitor cells. Leukemia 1993;7:625–9.[Medline]
33. Williams LM, Ricchetti G, Sarma U, Smallie T, Foxwell BM. Interleukin-10 suppression of myeloid cell activation—a continuing puzzle. Immunology 2004;113:281–92.[CrossRef][Medline]
34. Jacobsen SE. IL12, a direct stimulator and indirect inhibitor of haematopoiesis. Res Immunol 1995;146:506–14.[Medline]
35. Yssel H, Schneider P, Spits H. Production of IL4 by human T cells and regulation of differentiation of T-cell subsets by IL4. Res Immunol 1993;144:610–6.[CrossRef][Medline]
36. Fuste B, Escolar G, Marin P, et al. G-CSF increases the expression of VCAM-1 on stromal cells promoting the adhesion of CD34+ hematopoietic cells: studies under flow conditions. Exp Hematol 2004;32:765–72.[Medline]
37. Levesque JP, Takamatsu Y, Nilsson SK, Haylock DN, Simmons PJ. Vascular cell adhesion molecule-1 (CD106) is cleaved by neutrophil proteases in the bone marrow following hematopoietic progenitor cell mobilization by granulocyte colony-stimulating factor. Blood 2001;98:1289–97.[Abstract/Free Full Text]
38. Dominici R, Cattaneo M, Malferrari G, et al. Cloning and functional analysis of the allelic polymorphism in the transcription regulatory region of interleukin-1. Immunogenetics 2002;54:82–6.[CrossRef][Medline]
39. Asensi V, Alvarez V, Valle E, et al. IL-1 (–889) promoter polymorphism is a risk factor for osteomyelitis. Am J Med Genet A 2003;119:132–6.[Medline]
40. Rainero I, Bo M, Ferrero M, et al. Association between the interleukin-1 gene and Alzheimer's disease: a meta-analysis. Neurobiol Aging 2004;25:1293–8.[CrossRef][Medline]
41. Choi EH, Lee HJ, Yoo T, Chanock SJ. A common haplotype of interleukin-4 gene IL4 is associated with severe respiratory syncytial virus disease in Korean children. J Infect Dis 2002;186:1207–11.[CrossRef][Medline]
42. Choi EH, Foster CB, Taylor JG, et al. Association between chronic disseminated candidiasis in adult acute leukemia and common IL4 promoter haplotypes. J Infect Dis 2003;187:1153–6.[CrossRef][Medline]
43. Hoebee B, Rietveld E, Bont L, et al. Association of severe respiratory syncytial virus bronchiolitis with interleukin-4 and interleukin-4 receptor polymorphisms. J Infect Dis 2003;187:2–11.[CrossRef][Medline]
44. Beghe B, Barton S, Rorke S, et al. Polymorphisms in the interleukin-4 and interleukin-4 receptor chain genes confer susceptibility to asthma and atopy in a Caucasian population. Clin Exp Allergy 2003;33:1111–7.[CrossRef][Medline]
45. Rockman MV, Hahn MW, Soranzo N, Goldstein DB, Wray GA. Positive selection on a human-specific transcription factor binding site regulating IL4 expression. Curr Biol 2003;13:2118–23.[CrossRef][Medline]
46. Timmann C, Fuchs S, Thoma C, et al. Promoter haplotypes of the interleukin-10 gene influence proliferation of peripheral blood cells in response to helminth antigen. Genes Immun 2004;5:256–60.[CrossRef][Medline]
47. Temple SE, Lim E, Cheong KY, et al. Alleles carried at positions –819 and –592 of the IL10 promoter affect transcription following stimulation of peripheral blood cells with Streptococcus pneumoniae. Immunogenetics 2003;55:629–32.[CrossRef][Medline]
48. Eskdale J, Gallagher G, Verweij CL, et al. Interleukin 10 secretion in relation to human IL-10 locus haplotypes. Proc Natl Acad Sci U S A 1998;95:9465–70.[Abstract/Free Full Text]
49. Chong WP, Ip WK, Wong WH, et al. Association of interleukin-10 promoter polymorphisms with systemic lupus erythematosus. Genes Immun 2004;5:484–92.[CrossRef][Medline]
50. Lin MT, Storer B, Martin PJ, et al. Relation of an interleukin-10 promoter polymorphism to graft-versus-host disease and survival after hematopoietic-cell transplantation. N Engl J Med 2003;349:2201–10.[Abstract/Free Full Text]
51. Lyon H, Lange C, Lake S, et al. IL10 gene polymorphisms are associated with asthma phenotypes in children. Genet Epidemiol 2004;26:155–65.[CrossRef][Medline]
52. Scassellati C, Zanardini R, Squitti R, et al. Promoter haplotypes of interleukin-10 gene and sporadic Alzheimer's disease. Neurosci Lett 2004;356:119–22.[CrossRef][Medline]
53. Hoppe C, Klitz W, Cheng S, et al. Gene interactions and stroke risk in children with sickle cell anemia. Blood 2004;103:2391–6.[Abstract/Free Full Text]
54. Taylor JG, Tang DC, Savage SA, et al. Variants in the VCAM1 gene and risk for symptomatic stroke in sickle cell disease. Blood 2002;100:4303–9.[Abstract/Free Full Text]
55. Kuersten S, Goodwin EB. The power of the 3' UTR: translational control and development. Nat Rev Genet 2003;4:626–37.[CrossRef][Medline]

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