IL15 and obesity due to melanocortin 4 receptor deficiency: Stimulation of T lymphocytes with IL-15 (a proinflammatory cytokine abundant in individuals with obesity and fatty liver, and who consume a high-fat diet; (Cepero-Donates et al., 2016)) increases the expression of the CPT1A gene, which, in turn, promotes the oxidation of fatty acids, which are vital for providing energy for cytotoxic T lymphocyte proliferation and survival (Van der Windt et al., 2013).