Cytokine production induced by binding and processing of calcium oxalate crystals in cultured macrophages.

Deposition of calcium oxalate (CaOx) crystals in the renal interstitium is common in humans with primary oxalosis and secondary hyperoxaluria, as well as in kidneys of rats with CaOx nephrolithiasis. In vivo, macrophages and multinucleated giant cells mostly encapsulate these crystals. To investigate whether macrophages are able to dispose of CaOx crystals after phagocytosis, we used a nontransformed macrophage cell line derived from mouse spleen progenitors. Cytokine assays showed that in response to crystal binding and phagocytosis, these macrophages release tumor necrosis factor-alpha. This release was evident at 8 hours, maximal at 24 hours, and decreased to control values after 48 hours of incubation with crystals. A very low but significant release of interleukin-6 into the culture medium was only noticed after 32 hours. Radiochemical experiments showed that these cells bind 38.8% of the CaOx crystals added. After 4 days, all internalized crystals had been dissolved and their molecular constituents released into the extracellular environment. Confocal laser scanning microscopy followed by morphometrical analyses confirmed these results. Long-term (survival) analyses showed that in the interval under study and at the crystal doses used, cell viability was not significantly affected. These findings support the view that properly functioning macrophages are able to remove CaOx deposits from the renal interstitium and that these cells produce inflammatory cytokines before crystal dissolution.