TNF and obesity due to melanocortin 4 receptor deficiency: PTPN2-knockout C57BL/6 mice have a normal lifespan but showed a reduction in obesity symptoms and increased insulin sensitivity [36], but PTPN2-knockout BALB/C mice exhibited a significant systemic inflammatory response, and a large amount of IL-12, IFNγ, and TNFα infiltrated in the spleen and nonlymphoid tissues [25, 37].