The severity of symptoms in the C57BL/6lpr/lpr-PD-1-/- mice resembled that of the MRL-FASlpr/lpr mouse, which develops lupus-like symptoms much earlier than the C57BL/6lpr/lpr. PD-1 deletion in the MRL mouse resulted in the development of myocarditis and death of the mice by week 10 (45). Here, PDCD1 is linked to systemic lupus erythematosus.