P1800RITUXIMAB ENHANCES THE EXPRESSION OF INTERLEUKIN-6 VIA TOLL-LIKE RECEPTOR 3 SIGNALING IN HUMAN PODOCYTE

Abstract

Abstract Background and Aims The etiology of idiopathic nephrotic syndrome (INS) in children remains unclear, but it is well known that viral infections often cause relapses of INS. Since toll-like receptor 3 (TLR3), a ligand of viral dsRNA exists in podocytes, dysregulation of TLR3 signaling in podocytes may be involved in the pathogenesis of INS. Recently, rituximab (RTX) a specific antibody to human CD20, has been successfully used to treat children with intractable nephrotic syndrome (frequent relapse nephrotic syndrome, FRNS, and steroid dependent nephrotic syndrome, SDNS). It has been reported that depletion of B cell is main mechanism of RTX treatment. However, some patients experienced recurrence before peripheral blood B cell recovery, whereas selected patients have sustained remission even after peripheral blood B cell recovery. Considering that dramatic effects of RTX in the treatment of INS, it is speculated that some B cell-independent mechanisms of RTX exist. In this context, some recent studies have reported a direct effect of RTX on podocyte, targeting sphingomyelinase phosphodiesterase acid-like 3b (SMPDL3b), but detailed mechanisms remain to be determined. In this study, we examined whether RTX influences TLR3 signaling in cultured human podocyte. Method Immortalized human podocytes in culture were treated with polyinosinic-polycytidylic acid (poly IC), a synthetic analogue of viral dsRNA. RTX were added before or after the treatment of poly IC. Then, expression of interleukin (IL)-6 were measured using real time RT-PCR and ELISA. Direct binding of RTX to podocyte were confirmed by immunofluorescence. Results Poly IC induced the expression of IL-6 in cultured human podocyte in a concentration and time-dependent manner. IL-6 expression induced by poly IC were enhanced in both mRNA and protein level by pretreatment of RTX. RTX itself were apparently stained on podocyte by immunofluorescence. Conclusion RTX binds directly to cultured human podocyte and enhances the IL-6 expression induced by poly IC. Since IL-6 from podocyte was reported to be engaged in regulating glomerular inflammation by cross-talk with endothelial cells, exploring the role of enhanced IL-6 from podocyte by RTX, at least in a part, suggests a direct mechanism of RTX in treating intractable nephrotic syndrome in children.