31 reported that T-bet Tg mice developed dermatitis characterized by swollen, flaky and scaly skin in regions without body hair, which is pathologically similar to that seen in contact dermatitis, and that CD4+ T cells differentiated mainly into Th1 cells. Moreover, spontaneous development of characteristic lupus-like mild proliferative glomerulonephritis with predominant IgG3 deposition was reported in ageing C57BL/6 PD-1 KO mice, together with the appearance of arthritis characterized by increased lining layers of synovial tissues in foot joints 23. Here, CD4 is linked to systemic lupus erythematosus.