Association between CCL18 levels and the development of asthma and sensitisation
Proceeding with the chemokines showing the strongest consistent associations cross-sectionally, we set up GEE models studying each chemokine at each age separately in relation to various intervals of asthma and sensitisation development to study longitudinal relationships over time. These models take into account correlations within individuals, and as the data are not independent over time, this provides an advantage of running both the GEE and logistic regression models. Consistent longitudinal patterns were only revealed for circulating levels of CCL18 at ages 1 and 8 (Figure 5).
Asthma: In a longitudinal model including information on asthma from four time-points (ages 5, 8, 11 and 16), we observed a significant association between increasing CCL18 levels at age 1 year and the higher risk of asthma from early school age to adolescence (OR=2.9, 95% CI 1.1-7.6, p=0.028). Similarly, higher CCL18 levels at ages 1 (OR=3.5, 95% CI 1.3-9.8, p=0.01) and 8 years (OR=3.0, 95% CI 1.6-5.9, p=0.001) were associated with an increased risk of asthma between ages 8 and 16 years.
Sensitisation: In a longitudinal model including information on SPTs from five time-points (ages 3-16 years), the odds of becoming sensitised increased significantly with increased CCL18 concentrations at age 1 (OR=3.1, 95% CI 1.2-8.3, p=0.022). Similarly, the odds ratios for developing sensitisation between the ages 8 and 16 years increased significantly with increasing CCL18 levels at ages 1 (OR=3.5, 95% CI 1.3-9.9, p=0.018) and 8 years (OR=3.0, 95% CI 1.5-5.9, p=0.002).