Research Modification of the Interleukin-6 Response to Air Pollution by Interleukin-6 and Fibrinogen Polymorphisms Petter Ljungman,1,2 Tom Bellander,2 Alexandra Schneider,3 Susanne Breitner,3 Francesco Forastiere,4 Regina Hampel,3 Thomas Illig,3 Bénédicte Jacquemin,5,6 Klea Katsouyanni,7 Stephanie von Klot,3,8 Wolfgang Koenig,9 Timo Lanki,10 Fredrik Nyberg,2,11 Juha Pekkanen,10 Riccardo Pistelli,12 Christos Pitsavos,13 Mårten Rosenqvist,1 Jordi Sunyer,5,14,15,16 and Annette Peters 3 1Department of Cardiology, Karolinska Institutet, Stockholm South Hospital, Stockholm, Sweden; 2Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; 3Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Epidemiology, Munich, Germany; 4Department of Epidemiology, Local Health Authority, RME, Rome, Italy; 5Centre for Research in Environmental Epidemiology, Barcelona, Spain; 6Institut national de la santé et de la recherche médicale U780, Epidemiology and Biostatistics, University Paris-Sud, IFR69, Villejuif, France; 7Department of Hygiene and Epidemiology, University of Athens Medical School, Athens, Greece; 8Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; 9Department of Internal Medicine II—Cardiology, University of Ulm Medical Center, Ulm, Germany; 10Environmental Epidemiology Unit, National Public Health Institute, Kuopio, Finland; 11AstraZeneca R&D, Mölndal, Sweden; 12Department of Pneumology, Catholic University, Rome, Italy; 13First Cardiology Clinic, Ippokration Hospital, University of Athens, Athens, Greece; 14Municipal Institute of Medical Research, Barcelona, Spain; 15CIBER in Epidemiology and Public Health, Barcelona, Spain; 16Department of Health and Experimental Sciences, University Pompeu Fabra, Barcelona, Spain Background : Evidence suggests that cardiovascular effects of air pollution are mediated by inflammation and that air pollution can induce genetic expression of the interleukin-6 gene (IL6). o Bjectivs : We investigated whether IL6 and fibrinogen gene variants can affect plasma IL-6 responses to air pollution in patients with cardiovascular disease. Methods : We repeatedly determined plasma IL-6 in 955 myocardial infarction survivors from six European cities (n = 5,539). We conducted city-specific analyses using additive mixed models adjusting for patient characteristics, time trend, and weather to assess the impact of air pollutants on plasma IL-6. We pooled city-specific estimates using meta-analysis methodology. We selected three IL6 single-nucleotide polymorphisms (SNPs) and one SNP each from the fibrinogen α-chain gene (FGA) and β-chain gene (FGB) for gene–environment analyses. r esult : We found the most consistent modifications for variants in IL6 rs2069832 and FBG rs1800790 after exposure to carbon monoxide (CO; 24-hr average; p-values for interaction, 0.034 and 0.019, respectively). Nitrogen dioxide effects were consistently modified, but p-values for interaction were larger (0.09 and 0.19, respectively). The strongest effects were seen 6–11 hr after exposure, when, for example, the overall effect of a 2.2% increase in IL-6 per 0.64 mg/m3 CO was modified to a 10% (95% confidence interval, 4.6–16%) increase in IL-6 (p-value for interaction = 0.002) for minor homozygotes of FGB rs1800790. c onclusi : The effect of gaseous traffic-related air pollution on inflammation may be stronger in genetic subpopulations with ischemic heart disease. This information could offer an opportunity to identify postinfarction patients who would benefit more than others from a cleaner environment and antiinflammatory treatment. k ey words : air pollution, fibrinogen, gene–environment interaction, interleukin-6, myocardial infarction survivors, polymorphisms. Environ Health Perspect 117:1373–1379 (2009). doi:10.1289/ ehp.0800370 available via http://dx.doi.org/ [Online 6 April 2009] Although air pollution has been recognized as a risk factor for cardiovascular morbid- ity and mortality (Brook et al. 2004), its mechanism of action remains largely unclear. Inflammation has been proposed as a pos- sible mechanism, and this possibility is sup- ported by experimental models (Donaldson et al. 2003; Niwa et al. 2008; Vogel et al. 2005) and population studies (Rückerl et al. 2006, 2007; Schwartz 2001). A key player in modulating the inflammatory response is interleukin-6 (IL-6), a pleiotropic cytokine shown to be associated with increased risk of cardiovascular morbidity and mortality (Rattazzi et al. 2003). Levels of IL-6 in plasma may be affected by specific genetic variations of both the gene encoding IL-6 (IL6; GenBank acces- sion number M18403) (Bennermo et al. 2004; Burzotta et al. 2001) and genes encoding the fibrinogen protein [α-chain (FGA), β-chain (FGB), and γ-chain (FGG); GenBank accession numbers NM_000508, NM_005141, and NM_021870, respectively] (Mannila et al. 2007; National Center for Biotechnology Information 2009). Because IL-6 principally stimulates fibrinogen produc- tion (Dalmon et al. 1993), a possible explana- tion for increased IL-6 levels in association with certain fibrinogen gene polymorphisms is a positive feedback mechanism where fibrinogen products (fibrin) increase IL-6 production in monocytes and macrophages (Ritchie et al. 1982; Robson et al. 1994; Szaba and Smiley 2002). Several studies have shown expression of the IL6 gene to be induced by air pollu- tion (Quay et al. 1998; Vogel et al. 2005; Watterson et al. 2007), but no studies have examined induction of fibrinogen genes or Environmental Health Perspectives • volume 117 | number 9 | September 2009 examined variants of the IL6 gene and how they may possibly lead to differences in indi- vidual susceptibility to air pollution. In pre- vious analyses from this study population, genetic polymorphisms of fibrinogen have been associated with increased fibrinogen plasma levels (Jacquemin et al. 2008) and modified the fibrinogen response to ambient particulate matter (PM) (Peters et al. 2009). In light of a positive feedback mechanism of fibrinogen levels on IL-6 levels, poly- morphisms of fibrinogen may potentially affect IL-6 levels differently through dif- ferences in transcription rate of fibrinogen. Indeed, combinations of polymorphisms in the IL6 and fibrinogen genes may interact to further increase IL-6 levels. Myocardial infarction (MI) survivors have a compromised long-term prognosis, making relative risk reduction particularly advantageous. We hypothesized that the moderate effect of air pollution seen on inflammatory markers in previous stud- ies is stronger in MI survivors with specific Address correspondence to P. Ljungman, Unit of Environmental Health, Institute of Environmental Medicine, Karolinska Institutet, Norrbacka plan 3, SE-171 76, Stockholm, Sweden. Telephone: 46-73- 205-53-30. Fax: 46-8-737-37-70. E-mail: petter. ljungman@ki.se Supplemental Material is available online (doi: 10.1289/ehp.0800370.S1 via http://dx.doi.org/) The AIRGENE study was funded by the European Union’s 5th Framework Program, key action num- ber 4: “Environment and Health,” contract num- ber QLRT-2002-02236. The statistical and genetic group was funded by the National Genome Research Net of the German Ministry of Education and Research, the “Sonderforschungsbereich-SFB-386,” and the Munich Center of Health of the Ludwig- Maximilians-Universität München. F.N. is employed by AstraZeneca, and AstraZeneca also supports his academic part-time adjunct position as Lecturer in Molecular Epidemiology at Karolinska Institutet. AstraZeneca did not contribute any direct financing to this study. The remaining authors declare they have no competing financial interests. Received 5 November 2008; accepted 6 April 2009. 1373