To test whether accumulated human S100A8+ immune cells could cause BAT aging, isolated human S100A8+ immune cells or S100A8− immune cells were transferred to 2-month-old immuno-deficiency NOD-SCID (nonobese diabetic/severe combined immune-deficient) mice to establish a humanized-mouse model (Fig. 6d). The gene discussed is S100A8; the disease is immunodeficiency disease.