1838 Reactive Oxygen Production during Phagocytosis

The giomerular mesangium is a supporting structure that includes the mesangial cells and an intercellular substance, the mesangial matrix. Mesangial cells are steilate in shape and resemble morphologically smooth muscle cells (1, 2). They contract in response to binding of angiotensin II (3, 4) and vasopressin (4). They also produce prostaglandins (PG) 1 (5) and synthesize the mesangial matrix (6). In addition to these contractile and biosynthetic properties, phagocytic function has been ascribed to mesangial cells, but the data regarding this point are controversial. Following their intravenous administration to rats, macromolecules such as thorium dioxide, colloidal gold, and ferritin (7) are found very rapidly within the mesangial cells. However, other materials, particularly antigenantibody complexes, have been observed only in the mesangial matrix and very rarely within the cells (8), and Striker et al. (9) demonstrated that only the marrow-derived monocytes present within the mesangium were able to phagocytize the immune complexes. Recently, using heat-aggregated antiperoxidase immunoglobulins (Ig), Mancilla-Jimenez et al. (10) showed that mesangial cells could incorporate this material following its in vivo administration. They concluded that mesangial cells possess a vacuolar apparatus capable of ingesting heat-aggregated Ig. It was also shown in in vitro studies that cultured mesangial cells did not phagocytize latex particles (1 1), and did not possess C3 and IgG Fcbinding sites (12). These results contradict the previous findings of Camazine et al. (13) who, 18-24 h after isolation, obtained a population of glomerular cells, probably comprising mainly mesangial cells, which were highly phagocytic for opsonized zymosan particles and had the potential to develop Fc and C3 receptors. Schreiner et al. (14) have concluded that the phagocytic ability belongs to a well-defined fraction of the mesangial cells bearing Ia determinants. Only these cells, which represented a very small percentage of the total glomerular cell population, were able to phagocytose latex beads in vitro or heat-aggregated