PDCD4 and systemic lupus erythematosus: miR-21 contributes to aberrant CD4+ T cell responses in human SLE by targeting PDCD4, while inhibiting miR-21 in vitro improves abnormal CD4+ T cell responses, including the production of IL-10, and the expression of CD40L, as well as the capability to support B cell development, which indicates the pathogenic role of miR-21 in SLE (113).