GRK6 and rheumatoid arthritis: In vitro studies with proinflammatory cytokines IL-6 and IFN-γ induce GRK2 protein downregulation in human peripheral blood mononuclear cells (PBMCs) and GRK2 and GRK6 levels are reduced in PBMCs from patients with rheumatoid arthritis (RA) and in splenocytes from experimental mouse models of multiple sclerosis (MS) [2].