IL-1β and
IL-18 are proinflammatory
cytokines that contribute to renal
immune complex disease, but whether IL-1β and
IL-18 are mediators of intrinsic glomerular
inflammation is unknown. In contrast to other
cytokines the secretion of IL-1β and
IL-18 requires a second stimulus that activates the inflammasome-ASC-caspase-1 pathway to cleave pro-IL-1β and -IL-18 into their mature and secretable forms. As the NLRP3
inflammasome and caspase-1 were shown to contribute to postischemic and postobstructive tubulointerstitial
inflammation, we hypothesized a similar role for NLRP3, ASC, and caspase-1 in glomerular immunopathology. This concept was supported by the finding that lack of IL-1R1 reduced antiserum-induced focal segmental
necrosis, crescent formation, and tubular
atrophy when compared to wildtype mice. Lack of
IL-18 reduced tubular
atrophy only. However, NLRP3-, ASC- or caspase-1-deficiency had no significant effect on renal histopathology or
proteinuria of serum
nephritis. In vitro studies with mouse glomeruli or mesangial cells, glomerular endothelial cells, and podocytes did not reveal any pro-IL-1β induction upon LPS stimulation and no caspase-1 activation after an additional exposure to the NLRP3 agonist
ATP. Only renal dendritic cells, which reside mainly in the tubulointerstitium, expressed pro-IL-1β and were able to activate the NLRP3-caspase-1 axis and secrete mature IL-1β. Together, the NLRP3-ASC-caspase-1 axis does not contribute to intrinsic glomerular
inflammation via glomerular parenchymal cells as these cannot produce IL-1β during sterile
inflammation.