CD8A and obesity due to melanocortin 4 receptor deficiency: In this study, we showed that upregulated β2-microglobulin expression in hypertrophic adipocytes during obesity not only mediated the activation of adipose-resident CD8+ T cells in a cell contact-dependent manner but also facilitated iron overload and the ferroptosis of adipocytes, thereby promoting the M1 polarization of adipose tissue macrophages.