Context: Low-grade inflammation is associated with insulin resistance and precedes the onset of type 2 diabetes mellitus (T2DM) in adults, but there are no comparable data in youth.

Objective: To characterize the pattern of subclinical immune activation that is associated with indices of obesity and insulin resistance in youth and to analyze whether this association is explained by obesity.

Design: This is a cross-sectional study.

Setting: Medical check-up of schoolchildren by the Public Health Office in Düsseldorf (Germany).

Participants: 519 adolescents (mean 15.5±0.8 years).

Main Outcome Measures: BMI and waist circumference (WC) as indices of obesity; fasting glucose, insulin and homeostasis model assessment of insulin resistance (HOMA-IR); serum concentrations of tumor necrosis factor (TNF)-, interleukin (IL)-6, IL-8, IL-18, monocyte chemoattractant protein (MCP)-1, interferon--inducible protein (IP)-10 and adiponectin as immunological variables.

Results: In age, sex and lipid-adjusted analyses, IL-6, IL-18, IP-10 and adiponectin (inversely) were associated with both BMI and WC (all P0.002). None of the immune markers was related to glucose, but IL-6, IL-18 and adiponectin (inversely) were associated with insulin and HOMA-IR in age and sex-adjusted models. Adjustment for BMI or WC indicated that a considerable proportion of these associations may be mediated by obesity.

Conclusions: We found that a differential low-grade immune activation is associated with parameters of obesity in adolescents. Moreover, there is evidence that IL-6, IL-18, IP-10 and adiponectin (inversely) are associated with insulin resistance and that these association can mainly be attributed to obesity.