Receptor mediated endocytosis by mesangial cells modulates transmigration of macrophages

Background: Accumulation of immune complexes in the mesangium is a common f inding. Since migration of macrophages (M phi) in the mesangium has been de monstrated to he an important event in the development of glomerular lesion s, we studied the role of immune complexes and mesangial cell (MC) interact ion in the transmigration (Tm) of M phi. Methods: To determine the effect o f MC and immune complexes (aggregated IgG, IgGAg) on transmigration of M ph i. MC were incubated with or without IgGAg in the lower compartment of a mo dified Boyden Chamber. To determine the effects of the secretory products ( as a result of endocytosis of IgGAg by mesangial cells), MC-IgAg conditione d media was prepared and placed in the lower compartment of the Boyden cham ber: We evaluated the effects of MC alone, MC + IgGAg, or MC-IgGAg conditio ned media on the transmigration of macrophages across a filter. To determin e the effect of free radicals on MC-IgAg, endocytosis-induced M phi migrati on we evaluated the effect of free radical scavengers such as dimethyl thio urea (DMTU) and tetramethylthiourea (TMTU) in MC-IgAg endocytosis-induccd M phi migration. To determine the role of chemokines, in MC-IgAs endocytosis induced M phi migration we evaluated the effect of ani-MCP-l antibodies on MC-IgAg endocytosis-induced M phi migration, and also studied the effects of IgAg on MC mRNA expression of MCP-1 and RANTES. In addition, we evaluate d the role of Fe receptors and actin cytoskeleton of MC in transmigration o f M phi. Results: Mesangial cell endocytosis of IgG aggregates (IgGAg) is a ssociated with enhanced (P < 0.001) transmigration of M<phi> (control, 11.2 +/- 0.2 vs. MC + IgGAg. 22.1 +/- 0.9 migrated M phi /field). IgGAg also in duced MC mRNA expression for RANTES and MCP-1 on MC. DMTU and TMTU attenuat ed (P < 0.001) the MC + IgGAg-induced migration of M<phi> as well as IgGAg- induced mRNA expression for RANTES and MCP-1. MC and IgGAg interaction prod ucts (MC-IgGAg conditioned media) also increased (P < 0.01) transmigration of Md (control, 18.3 +/- 1.7 vs. MC-IgGAg conditioned media, 30.7 +/- 0.6 M <phi>/field). This effect of MC-IgGAg conditioned media on the migration of macrophages was dose dependent. Anti-MCP-1 antibody partially inhibited MC -IgGAg-induced migration of macropahges. MC and monomeric IgG (MIgG) intera ction (MC-MIgG conditioned media) showed a lower (P < 0.05) migration of M< phi> when compared to the MC-IgCAg conditioned media. MC-IgGAg conditioned media prepared from cytochalasin B pretreated MCs also showed a lower (P < 0.001) migration of M<phi> when compared with MC-IgGAg conditioned media-in duced migration. Conclusions: These results: indicate that MC-IgGAg conditi oned media-induced transmigration of macrophages may be mediated through th e generation of RANTES and MCP-1 by MC.