Neutral Red

This compound (3-amino-7-dimethyl-amino-2-methylphenazine hydrochloride) is one of the most common vital steins in order to distinguish living from dead cells. This compound, when brought onto living cells, enters the cytoplasm and colorates lysosomes. Thus loss of neutral red uptake is correlated to loss of viability. The uptake of this compound, however, depends on the cell’s capacity to maintain pH gradients through ATP production. At physiological pH, this dye test has a net charge close to zero. Thus the product is able to enter into the cell. In lysosomes there is a proton gradient to maintain a somewhat lower pH than that of the surrounding cytoplasm. As a consequence, the compound becomes charged and is thus retained inside the lysosomes and can be noted when using a light microscope or other measurement systems.

This neutral red test is used, e.g., in trials of cytotoxicity of new medicaments, to check cytotoxic T-cell populations and status of unicellular parasites in...