PDCD1 and systemic lupus erythematosus: In the study “Upregulated PD-1 expression is associated with the development of systemic lupus erythematosus, but not the PD-1.1 allele of the PDCD1 gene,” Q. Jiao et al. found that the PD-1 expression levels of systemic lupus erythematosus (SLE) patients were significantly increased compared with those of the healthy controls.