UPTAKE OF NUCLEOSOMES - EVIDENCE FOR RECEPTOR-MEDIATED MESANGIAL CELL-BINDING

DNA-containing immune complexes (IC) are believed to have a central ca usal role in the glomerulonephritis of systemic lupus erythematosus. E xtracellular DNA which provides the antigenic source for these ICs cir culates as oligonucleosomes (ON). The in vivo glomerular uptake of rad iolabeled ON in rats, as well as its binding by cultured rat mesangial cells, was examined. The data show that the binding of ON to kidney, and specifically glomeruli, was almost fourfold greater than that of p urified DNA. Uptake appeared dose-dependent and saturable, while there were no differences in hepatic or splenic uptake. Most of the nucleos omal DNA recovered from glomeruli was TCA-precipitable, and on gel ele ctrophoresis was about 100 to 300 bp, a size sufficient to allow forma tion of large ICs. In vitro studies demonstrated that ON are bound by cultured mesangial cells in a dose-dependent and saturable manner, wit h a dissociation constant of 1.25 x 10(-10) M/liter and 750 binding si tes per cell. Autoradiography of cell cultures incubated with radiolab eled ON showed deposition along the plasma membrane which was inhibite d by excess unlabeled ON. The data show that binding of ON to glomerul i exceeds that of purified DNA and may be mediated by histones. ON bin d to mesangial cells in a receptor-mediated fashion. The data support the hypothesis of in situ formation of DNA-containing ICs and suggest a role for the mesangial cell in lupus glomerulonephritis.