CD274 and systemic lupus erythematosus: While disruption of PD-1/PD-L1 signalling induces SLE-like autoimmune disease with dominant cardiac involvement (Nishimura and Honjo, 2001; Nishimura et al., 2001), the relative contributions of the direct effects of PD-L1 depletion in the heart versus the indirect effects mediated by systemic autoimmunity are not yet understood and need to be carefully considered.