Induction of iNOS and NO production by RAW264.7 cells exposed to MWCNTs. Quiescent cultures of RAW264.7 cells were exposed to an increasing concentration of MWCNTs or CBNPs. A) Western blot analysis showed induction of iNOS protein with increasing concentrations of MWCNTs with no induction by CBNPs. Levels of β-actin are shown as a constitutive control protein in RAW264.7 cells. Numeric values above the Western blot represent the fold-increase in relative densitometric intensity of each iNOS band relative to control (zero) nanoparticle treatment which was normalized to 1.0. B) MWCNTs (solid bars), but not CBNPs (open bars), increased levels of sodium nitrite (NaNO2) in RAW264.7 cell supernatants as a measure of NO. *Significantly different from the vehicle control (p < 0.05).