[Charge interactions of immune deposits in glomeruli (experimental study)]

An i.v. injection of 8-40 mg (kg cationized and heat-aggregated rabbit or human Ig (cat-aggr RIg,-HuIg; pI 9.5) elicited a strong diffuse linear fixation in rat glomerular capillaries revealed by one-step immunofluorescence or immunoenzyme histochemistry 1 and 2 h post-injection. Preferential binding to the lamina rara externa (LRE) was documented in ultrastructure by preembedding and postembedding assays (HRP-coupled antibody and protein A-colloidal gold, respectively). After 24 and 48 h the glomeruli were negative. Polyethylenimine (PEI)-reactive polyanion of LRE was significantly reduced 1 h after cat-aggr-Ig; depletion persisted even after 48 h. Non-cationized Ig aggregates did not bind to the glomerular capillaries. A subsequent i.p. injection of swine anti-rabbit-Ig antibody (SwAR, 15 mg i.p. after 4 h) produced the same linear binding of both two antigens which, however, persisted after 10 days and assumed a granular pattern. After presensitization with RIg (1-2 mg i.p. or s.c.; 4 days before cat-aggr RIg) the early linear fixation underwent a gradual transformation into the granular pattern and deposits of mesangial, rarely of epimembranous type were found 1 week after cat-aggr RIg and later. RIg and SwIg were proved in both types of deposits. After 2 weeks both rat Ig and C 3 were present, too. Rarefaction of deposits and their concentration in the vascular poles took place during 3 months, and deposits also appeared in the media of vas afferens. The antigen load did not produce an acute glomerulonephritis or significant proteinuria; slight focal mesangial sclerosis and a discrete increase in serum creatinine were noted after 2-3 months. To sum up: The one-shot charge interaction is prompt but short-lived whereas the local binding of additional proteins, especially after a specific preimmunization, significantly prolongs the contamination of glomeruli and promotes the build-up of immune complex-type deposits which gradually retreat to the mesangial stalk and vascular pole.