RIPK1 and systemic lupus erythematosus: Patients with SLE showed significantly decreased levels of TNF adaptor proteins, TNF receptor-associated death domain (TRADD), Fas-associated death domain (FADD), TRAF2, and receptor-interacting protein kinase 1 (RIPK1) expressed in their peripheral blood mononuclear cells, according to Zhu et al. These levels were shown to be inversely associated to the SLE activity index [16,26].