Quantification of the inhibitory effect of eriochrome black and sodium nitrite on non-specific immunofluorescent staining.

To evaluate non-specific staining (NSS) of animal tissues by FITC-labelled immunoglobulins a model system was developed. HeLa cells were treated with labelled antisalmonella globulins and the fluorescence intensity of the cells was determined quantitatively by means of a fibre optic probe system. This system was used to determine the optimal treatment conditions (adequate concentrations, duration of treatment) using the two NSS-reducing agents eriochrome black and sodium nitrite. Approximately the same inhibitory effects (40-50 per cent using nitrite; about 85 per cent using eriochrome black) were obtained by conjugates of different F/P ratio values. The fibre optic probe system was also used to determine the effects of the above-mentioned agents on the NSS of liver sections. In this system, the NSS was strongly reduced by eriochrome black whereas nitrite treatment did not induce any inhibitory effect. The applicability of nitrite and eriochrome black as NSS-reducing agents was further demonstrated by the fact that they had no influence on the specific fluorescence intensity of salmonella bacteria. The effect of eriochrome black was also studied in clinical specimens infected with salmonella or tularemia bacteria.