Interaction of immune complexes with glomerular heparan sulfate-proteoglycans

The binding characteristics of cationic and more neutral immune complexes with heparan sulfate-proteoglycan enriched anionic sites of glomerular basement membrane and mesangial matrix were studied. Rat kidneys were treated either with buffers alone or buffers containing heparitinase or chondroitinase-ABC followed by perfusion with cationic or native immune complexes. Tissues were processed for immunofluorescence and transmission electron microscopy after fixation with glutaraldehyde or tannic acid glutaraldehyde. Kidneys perfused with radioiodinated immune complexes were processed for light and electron microscopic autoradiography. In addition, glomeruli from kidneys perfused with radioiodinated immune complexes were isolated and counted for radioactivity. By immunofluorescence the cationic immune complexes deposited linearly along the glomerular basement membrane. By electron microscopy, the cationic complexes localized mainly in the inner and outer layers of the glomerular basement membrane and to a certain extent in the mesangial matrix in a distribution that corresponded to previously documented anionic sites. Whereas heparitinase treatment abrogated the binding of cationic immune complexes in both glomerular basement membrane and mesangial matrix, chondroitinase-ABC treatment did not cause any decrease in binding. In contrast, more neutral immune complexes appeared to be nonspecifically trapped in the mesangium, and their distribution was unaffected by both enzymatic treatments. Light and electron microscopic autoradiography and counts of isolated glomeruli confirmed these findings. The results overall indicate that cationic immune complexes bind electrostatically to the heparan sulfate-proteoglycan enriched anionic sites of the glomerular basement membrane and mesangial matrix, while more neutral immune complexes are nonspecifically trapped in the mesangium of the renal glomerulus.