FIG. 6.

Schematic of interaction between particle and airway epithelial cells in altering iron homeostasis. Endocytosed particle will complex available iron from intracellular sites (A). The cell recognizes a functional deficiency in the metal and responds by generating more ferrireductant (e.g., superoxide) and increasing importers (e.g., divalent metal transporter; rectangular box spanning basolateral membrane [left side of cell]) (B). Following import of iron, a new homeostasis is achieved in the respiratory epithelial cells with higher intracellular iron concentrations allowing the cell to function while the particle sequesters some portion of the metal (C). Ferritin (rectangular box in the cell) is increased as a result of elevated cellular concentrations of iron. (A color image is available in the online version.)