RPS19 (
ribosomal protein S19), a component of the 40S small ribosomal subunit, has recently been identified to bind the pro-inflammatory
cytokine macrophage MIF (migration inhibitory factor). In vitro experiments identify RPS19 as the first endogenous MIF inhibitor by blocking the binding of MIF to its receptor CD74 and MIF functions on monocyte adherence to endothelial cells. In the present study, we sought to establish whether recombinant RPS19 can exert anti-inflammatory effects in a mouse model of
anti-GBM (glomerular basement membrane) GN (
glomerulonephritis) in which MIF is known to play an important role. Accelerated
anti-GBM GN was induced in C57BL/6J mice by immunization with sheep
IgG followed 5 days later by administration of sheep anti-mouse GBM serum. Groups of eight mice were treated once daily by
intraperitoneal injection with 6 mg of RPS19/kg of
body weight or an irrelevant control
protein (human
secretoglobin 2A1), or received no treatment, from day 0 until being killed on day 10. Mice that received control or no treatment developed severe crescentic
anti-GBM disease on day 10 with increased serum
creatinine, declined
creatinine clearance and increased
proteinuria. These changes were associated with up-regulation of MIF and its receptor CD74 activation of ERK (
extracellular-signal-regulated kinase) and NF-κB (nuclear factor κB) signalling, prominent macrophage and T-cell infiltration, as well as up-regulation of Th1 [T-bet and IFNγ (
interferon γ)] and Th17 [STAT3 (
signal transducer and activator of transcription 3) and IL (
interleukin)-17A] as well as IL-1β and TNFα (tumour
necrosis factor α). In contrast, RPS19 treatment largely prevented the development of glomerular crescents and
glomerular necrosis, and prevented renal dysfunction and
proteinuria (all P<0.001). Of note, RPS19 blocked up-regulation of MIF and CD74 and inactivated ERK and NF-κB signalling, thereby inhibiting macrophage and T-cell infiltration, Th1 and Th17 responses and up-regulation of pro-inflammatory
cytokines (all P<0.01). These results demonstrate that RPS19 is a potent
anti-inflammatory agent, which appears to work primarily by inhibiting MIF signalling.