Treatment of acute serum sickness by plasma ultrafiltration

The clinical value of a scaled-down prototype of an extracorporeal plasma ultrafiltration system for the treatment of acute serum sickness in rabbits was examined. The system uses two filters: the primary separates red cells from plasma, and the secondary filter excludes high molecular weight proteins from plasma. In vitro and in vivo experiments showed that the secondary filters rejected substantially more IgM (80-90%) than IgG (10-30%) or albumin (10%) and totally rejected immune complexes (IC) prepared in vitro. Two groups of rabbits were submitted to either sham filtration with the primary filter only (n = 5), receiving back the remixed components of their blood, or to the complete ultrafiltration protocol (n = 7), with removal of high molecular weight proteins and IC. Several parameters were studied longitudinally, such as circulating IC, which appeared to rise more slowly in animals whose blood was ultrafiltered, and total proteinuria, which appeared to remain at lower levels in the same animals. Histologic examination of the kidneys, collected after killing, showed evidence of glomerular IC deposition in three of five sham-treated animals (a similar frequency to that observed in a separate group of five rabbits with acute serum sickness), while one of six treated animals had evidence of glomerular deposition of IC. These observations are tentative because of the small number of animals in each group, but are encouraging. Further studies with larger groups of animals are needed to determine whether the observed effects are reproducible and to better characterize the factors directly related to the removal of circulating IC.