Ljungman et al. variants of inflammatory genes such as IL6 and the fibrinogen genes. We aimed to assess the influence of polymorphisms of the IL6, FGA, and FGB genes on the IL-6 response to air pollution and to explore the influence of gene–gene interactions on this effect. We present here results of a meta-analysis of six independent studies whose data were collected by a common protocol and that were designed to look at gene–air pollution interactions (Peters et al. 2007) Materials and Methods Patients. IL-6 concentrations were assessed in the AIRGENE study, a multicenter lon- gitudinal study of MI survivors from six European cities: Athens, Greece; Augsburg, Germany; Barcelona, Spain; Helsinki, Finland; Rome, Italy; Stockholm, Sweden (Peters et al. 2007). Subjects between 35 and 80 years of age who had experienced an MI between 4 months and 6 years before start of the study were recruited through population-based MI registries (KORA MI Registry Augsburg, and registries in Barcelona and Stockholm) or from administrative databases of hospital admissions (Athens, Helsinki, and Rome). Patients with MI or interventional procedures < 3 months before the beginning of the study or with chronic recurring inflammatory diseases such as Crohn’s disease were excluded. MI was defined based on the European Society of Cardiology/ American College of Cardiology Committee criteria (Anonymous 2000). Study protocols were approved by local ethics committees, and written consent was obtained from all patients before inclusion in the study. Patients were invited to participate in six to eight clinical visits between May 2003 and July 2004. The visits were scheduled every 4–6 weeks, on the same weekday and at the same time of the day to minimize the impact of weekly and circadian variation in biological processes and air pollution levels. The average number of visits per patient was 5.8, result- ing in 5,813 plasma samples. The subjects recruited were predominantly middle-age men who had survived one MI for > 2 years on average (Table 1). Field study. The fieldwork was based on standard operating procedures developed by the AIRGENE study group. At a baseline clinical visit, a single blood sample for DNA analysis was collected and stored at –80°C until shipment on dry ice for DNA isolation at the laboratory at the Helmholtz Zentrum München—German Research Center for Environmental Health in Neuherberg, Germany. Patients were also characterized at baseline with respect to comorbidities, smok- ing history, environmental tobacco exposures, socioeconomic status, regular exercise, and alcohol and medication intake. Measurements of blood pressure, body mass index (BMI), total cholesterol, high-density lipoprotein (HDL) cholesterol, glycosylated hemoglobin A1c (HbA1c), and N-terminal proB-type natri- uretic peptide (NT-proBNP) were performed. At each repeated clinical visit, including baseline, a short questionnaire was admin- istered regarding smoking behavior, time of last meal, and a 7-day recall of medication intake. In addition, a blood sample was col- lected for IL-6 assessment according to previ- ously described procedures (Peters et al. 2007). For quality assurance purposes, 102 randomly selected IL-6 duplicate samples from all cen- ters except Athens were analyzed, showing an average coefficient of variation of 13.8% (from 3.2% in Augsburg to 23.4% in Stockholm). Air pollution. Data on hourly means of carbon monoxide (CO), nitrogen dioxide (NO2), PM with an aerodynamic diameter ≤ 10 µm (PM10) or ≤ 2.5 µm (PM2.5), particle number concentration (PNC), air tempera- ture, and relative humidity were collected for each city (Rückerl et al. 2007) and aggregated to 6- and 24-hr running means on the basis of standard procedures (Katsouyanni et al. 1995). Inhalable (PM10) and thoracic (PM2.5) par- ticles were strongly correlated (overall r across cities for consecutive 24-hr means = 0.81), and local combustion-related pollutants were strongly correlated (CO and NO2, overall r = 0.68; and both also to PNC, overall r = 0.67 and 0.74, respectively). We also saw this over- all pattern in the single cities, with the excep- tion of Athens and Stockholm, which showed less correlation between CO and PNC. Table 1. Data on patient characteristics, IL-6 measurements, and air pollution concentrations in the AIRGENE study. 392.9 (10.8–3,799) 330.4 (14.0–3,348) 482.5 (12.5–9,308) 405.0 (19.1–6,174) 8,534 (5,834–10,519) 9,748 (7,247–11,625) 11,876 (7,085–14,440) 35,450 (21,094–46,963) 18,133 (10,492–24,278) 20,590 (11,872–26,913) 17,388 (10,604–22,456) aMean (range). bEver diagnosed by a physician. cMean (range) of the subject-specific means based on three to eight repeated measurements. dMean (25th–75th percentile) for consecutive 24-hr means across study period. ovlume 117 | number 9 | September 2009 • Environmental Health Perspectives Helsinki 182 69.8 64.4 (45–78) 28.8 (19.1–48.9) 0.3 (0.1–0.6) 5.9 (4.7–9.2) 1.7 9.2 (0–65.0) 2.7 (0.6–5.8) 3.1 (0.9–19.7) 5 Sep 2003 to 2 Jun 2004 0.31 (0.26–0.34) 28.6 (20.5–34.6) 8.2 (4.7–10.4) 17.1 (10.5–20.7) 81.9 1.7 1.8 1.5 1,081 0.76 0.38 0.25 0.60 Stockholm 193 71.0 64.0 (38–76) 27.6 (17.5–43.3) 0.3 (0.1–0.6) 5.1 (3.8–9.9) 0.5 12.2 (0–73.8) 2.3 (0.6–3.9) 2.6 (0.5–24.4) 30 Aug 2003 to 24 June 2004 0.29 (0.25–0.34) 18.4 (12.7–22.9) 8.8 (6.0–10.3) 17.8 (11.0–21.7) 86.5 1.8 1.8 1.5 1,146 0.56 0.53 0.30 0.23 Augsburg 187 81.8 61.9 (39–76) 28.9 (19.1–48.4) 0.3 (0.1–0.5) 5.6 (4.7–9.8) 0 15.2 (0–205.2) 2.1 (0.5–3.4) 2.5 (0.6–11.8) 14 May 2003 to 24 Feb 2004 0.58 (0.43–0.66) 40.0 (32.7–46.5) 17.4 (12.2–21.2) 33.1 (22.0–42.7) 88.2 1.8 1.9 1.5 1,067 0.53 0.61 0.60 0.77 Rome 132 87.1 62.5 (39–79) 27.7 (19.0–39.4) 0.2 (0.1–0.5) 5.4 (2.8–8.7) 9.1 22.0 (0–171.8) 2.7 (0.4–6.0) 3.0 (1.0–61.4) 20 Sep 2003 to 15 Jul 2004 1.40 (1.02–1.66) 67.0 (56.7–76.3) 24.6 (14.0–30.7) 42.1 (30.6–49.9) 87.1 1.8 1.9 1.4 728 0.75 0.70 0.71 0.87 Variable No. Sex (% male) Age (years)a BMI (kg/m2)a HDL/total cholesterola HbA1c (%)a NT-proBNP (pg/mL)a Current smokers (%) Pack-years (cigarettes only)a Time between last MI and study start (years)a First MI (%) Self-reported historyb Arrhythmia (%) Chronic bronchitis (%) Hypertension (%) Blood samples (n) IL-6 (pg/mL)c Air pollution measurement (study period)d CO (mg/m3) NO2 (µg/m3) PM2.5 (µg/m3) PM10 (µg/m3) PNC (per cm3) Pearson correlation CO NO2 PM2.5 PM10 PNC 1374 Barcelona 160 84.4 62.1 (37–81) 28.8 (19.4–43.5) 0.3 (0.1–0.5) 5.1 (3.8–9.8) 380.6 (11.3–7,057) 13.8 28.4 (0–193.2) 2.2 (0.4–5.9) 85.6 1.9 2.0 1.5 1,059 3.5 (0.8–28.5) 30 Aug 2003 to 16 Jun 2004 0.59 (0.45–0.70) 50.5 (39.3–60.4) 24.2 (13.5–29.7) 40.7 (25.1–49.2) 0.70 0.26 0.30 0.64 Athens 101 86.1 54.5 (38–75) 28.8 (20.9–46.4) 0.2 (0.1–0.6) 5.9 (3.7–10.5) 314.9 (11.0–4,855) 38.6 35.6 (0–174.0) 2.4 (0.5–5.0) 3.0 (0.8–22.4) 8 Sep 2003 to 30 Jul 2004 1.48 (0.95–1.68) 50.2 (42.0–59.0) 23.0 (14.9–29.1) 38.5 (27.1–46.4) 81.2 1.8 2.0 1.4 458 0.55 0.45 0.17 0.25 Total 955 79.0 62.2 (37–81) 28.4 (17.5–48.9) 0.3 (0.1–0.6) 5.5 (2.8–10.5) 389.1 (10.8–9,308) 8.1 18.8 (0–205.2) 2.4 (0.4–6.0) 85.3 1.8 1.9 1.5 5,539 3.0 (0.5–61.4) 0.78 (0.56–0.90) 42.4 (34.0–49.9) 17.7 (10.9–21.9) 31.6 (21.1–38.4) 0.69 0.55 0.47 0.67