PDCD1 and systemic lupus erythematosus: As a step forward to reconcile the inconsistencies in previous findings, a recent study revealed that the PD-1 pathway modulates Tfh-mediated humoral immunity by downregulating Tfr cells [97], which indicated that blocking PD-1 may preferentially influence the PD-1 function in Tfr cells and therefore mitigate lupus manifestations.