PHAGOCYTOSIS OF HEAT-AGGREGATED IMMUNOGLOBULINS BY MESANGIAL CELLS - AN IMMUNOPEROXIDASE AND ACID-PHOSPHATASE STUDY

Abstract

Mesangial cells (MC) phagocytose particulate material and nonimmune proteins. To determine if MC are able to engulf aggregated Ig, heat-aggregated antiperoxidase (HRP [horseradish peroxidase]) Ig were injected i.v. into Lewis rats. Sequential immunoelectron microscopic studies revealed that the injected material accumulates progressively in the extracellular compartment from 10 min-5 h and disappears afterward. This disappearance was related in part to the incorporation of aggregated anti-HRP Ig within phagosomes and phagolysosomes by MC. Quantitation of the phagocytic process showed that it starts as early as 10 min after injection and reaches its peak at 2.5 h. Endocytosis seems to be associated with the sequestration of injected Ig within large cytoplasmic invaginations and with micropinocytosis. Ultrastructural cytochemistry for acid phosphatase activity was performed. Quantitative studies showed that the number of acid phosphatase-labeled lysosomes in MC was .ltoreq. 7-fold in rats receiving aggregated anti-HRP Ig than in noninjected ones. Combined immunoperoxidase and acid phosphatase studies show that MC possess a vacuolar (lysosomal) apparatus capable of handling heat-aggregated Ig. It is not known whether these cells are also operational in the disposal of soluble immune complexes in spontaneous and experimental conditions. Observations suggesting the drainage of macromolecules from mesangium to the juxtaglomerular apparatus and from mesangium to the urinary space are presented.