While CD8+ T cells control the infiltration of macrophages and promote type-2 diabetes (Zhu et al, 2010), CD4+ T cells (presumably Th2 cells; Winer et al, 2009a, b) and Treg (Feuerer et al, 2009) reverse obesity and/or type-2 diabetes. Here, CD4 is linked to obesity due to melanocortin 4 receptor deficiency.