Characteristics of MTT as an indicator of viability and respiratory burst activity of human neutrophils.

In the present study, we have examined the suitability of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) for assessing the viability and respiratory burst activity of human neutrophils. MTT is a good indicator of the relative viability of neutrophils which have been in culture up to 24 h, if sufficient serum (10% fetal calf serum) is present in the medium and the cells being compared have been in culture for a similar period of time. However, it is not suitable for exact assessment of percent viable cells in a cell population with low viability. The effectiveness of MTT as an indicator of respiratory burst activity is demonstrated by the sharp increase in MTT reduction induced by respiratory burst stimuli and by the ability of superoxide dismutase to inhibit 75% of MTT reduction by stimulated neutrophils. Unlike nitroblue tetrazolium (which is reduced primarily intracellularly) and cytochrome c (which is reduced extracellularly), MTT is apparently reduced both intracellulary and extracellulary by activated neutrophils.