The lower level of  in the supernatant of hmp-infected cells could reflect an inability of the hmp mutant to detoxify NO to ; however, as the fur infected cells showed similar  accumulation, it is probably more likely that differences in  accumulation seen in both non-activated and activated tissue culture supernatants could be explained by the fact that iNOS activation may be infection-load dependent (Witthoft et al., 1998). This evidence concerns the gene FURIN and infection.