LEP and systemic lupus erythematosus: In SLE, the disease-associated higher leptin serum levels were negatively correlated with disease severity and number of Treg cells (Ma et al., 2015; Margiotta et al., 2016; Wang et al., 2017), and fasting-induced hypoleptinaemia was related to Treg population recovery in lupus-prone mice (Liu et al., 2012).