MAPK1 and systemic lupus erythematosus: It has been proposed that impaired ERK signaling pathway in SLE T cells contributes to the DNA hypomethylation that is a characteristic feature of SLE T cells that has also been reported in cells extracted from thymus and axillary lymph nodes of 20-week-old MRL/lpr mice (Quddus et al., 1993; Mizugaki et al., 1997).