ESR1 and rheumatoid arthritis: Moreover, the positive association between the ER-α expression, ERK1/2 phosphorylation and ROS/RNS production in RBCs further supported the hypothesis of involvement of a kinase-linked intracellular signaling whose activation, downstream to estrogen receptor, could play a key role in the induction of the mild oxidative stress detected in RBCs from RA patients (Vona et al., 2019).