CD4 and systemic lupus erythematosus: On further analysis of 16 lupus patients with a range of disease activity, oxidative-stress-induced peroxynitrite (ONOO−) in lupus CD4+ T-cells was found to contribute to site-specific decrease in phosphorylation of PKCδ T505, leading to functional loss of PKC and parallel reduction of ERK phosphorylation, which were significantly correlated with higher lupus disease activity [14].