Serum sST2 and sIL1RAcP vary with age and sex, but not with body mass index, in a lean versus obese cohort

<ns5:p> The IL-33 pathway is implicated in a number of inflammatory, allergic and metabolic conditions. Its receptor consists of a heterodimer of membrane-bound ST2 and IL1RAcP, both of which are also secreted in soluble form in the bloodstream. Levels of soluble ST2 and IL1RAcP (sST2 and sIL1RAcP) in the blood alter dynamically in response to a number of stimuli. In this study we focussed on how levels of sST2 and sIL1RAcP changed in lean (BMI &lt;26 kg/m <ns5:sup>2</ns5:sup> ) versus obese (BMI &gt; 30 kg/m <ns5:sup>2</ns5:sup> ) individuals, when taking into account other confounding factors such as age and biological sex. We found that both sST2 levels and sIL1RACP levels increased with age, while female sex predicted increased sIL1RAcP levels. Whether these factors were adjusted for or not, BMI had no effect on sST2 or sIL1RAcP levels. Therefore, in our study cohort of mildly obese versus lean subjects, we found that neither sST2 nor sIL1RAcP levels were affected by BMI, in opposition to previous studies on severely obese individuals. Therefore, sST2 and sIL1RAcp levels may only alter in inflammation associated with severe obesity. Our study also highlights the need to adjust for age and sex when using sST2 or sIL1RAcP as biomarkers of disease. </ns5:p>