Induction of iNOS followed by arginase-1 (Arg-1) expression in 3D cultures. Cells were exposed to 0.5 μg/ml (0.38 μg/cm2) of particulates. After 3, 7, 10 and 14 days, cells were fixed and co-immunostained for iNOS (green), Arg-1 (red), and counterstained with DAPI. Cells exposed to asbestos and MWCNT 1 and 3 showed earlier co-expression of iNOS and Arg-1. The increasing levels of expression of these two mediators indicate progression towards a profibrotic response. Samples were analyzed by confocal microscopy using the appropriate filters. Photographs are representative of Z-stacks of three individual samples. Magnification: 400×.