Obesity-related IL-18 Impairs T-Regulatory Cell Function and Promotes Lung Ischemia–Reperfusion Injury

Abstract

<b>Rationale:</b> Primary graft dysfunction (PGD) is a severe form of acute lung injury, leading to increased early morbidity and mortality after lung transplant. Obesity is a major health problem, and recipient obesity is one of the most significant risk factors for developing PGD. <b>Objectives:</b> We hypothesized that T-regulatory cells (Tregs) are able to dampen early ischemia-reperfusion events and thereby decrease the risk of PGD, whereas that action is impaired in obese recipients. <b>Methods:</b> We evaluated Tregs, T cells, and inflammatory markers, plus clinical data, in 79 lung transplant recipients and 41 liver or kidney transplant recipients and studied two groups of mice on a high-fat diet (HFD), which did ("inflammatory" HFD) or did not ("healthy" HFD) develop low-grade inflammation with decreased Treg function. <b>Measurements and Main Results:</b> We identified increased levels of IL-18 as a previously unrecognized mechanism that impairs Tregs' suppressive function in obese individuals. IL-18 decreases levels of FOXP3, the key Treg transcription factor, decreases FOXP3 di- and oligomerization, and increases the ubiquitination and proteasomal degradation of FOXP3. IL-18-treated Tregs or Tregs from obese mice fail to control PGD, whereas IL-18 inhibition ameliorates lung inflammation. The IL-18-driven impairment in Tregs' suppressive function before transplant was associated with an increased risk and severity of PGD in clinical lung transplant recipients. <b>Conclusions:</b> Obesity-related IL-18 induces Treg dysfunction that may contribute to the pathogenesis of PGD. Evaluation of Tregs' suppressive function together with evaluation of IL-18 levels may serve as a screening tool to identify obese individuals with an increased risk of PGD before transplant.