The stimulation of T lymphocytes by IL-15, a pro-inflammatory cytokine elevated in individuals with high-fat diets, obesity, and fatty liver disease [65], enhances the expression of the Carnitine palmitoyl transferase 1A gene (CPT1A), which promotes fatty acid oxidation, a crucial process providing energy for the proliferation and survival of CD8+ T cells [66]. The gene discussed is CD8A; the disease is obesity due to melanocortin 4 receptor deficiency.