IL6 and COVID-19: Likewise, Jia et al. found the levels of IL-1β, TNF-α and IL-6 increased with the severity of COVID-19, and TCA cycle-related metabolites such as aspartate, creatine, malate and alpha-ketoglutaric acid (α-KG) were positively correlated with the expression of IL-1β, TNF-α and IL-6 (Jia et al., 2021).