A Comparison of Fluorescein and I131 as Labels for Determining the«in vivo» Localization of Anti-Tissue Antibodies

Abstract

Fixation of localizing anti-tissue antibodies in vivo as determined by fluorescein-labeled antibody stain techniques and by radioactive techniques are compared. The fluorescein stain technique has the advantage of histological precision, i.e. localization of antibody may be determined on a cellular basis. However, large concentration of antibody must be present for detection, i.e., 1.4 x 10-4 ug/mm2. The precision of localization as determined by radioautographs with I131 is decreased, but location of much less antibody is possible. Both radioautography and fluorescein stain techniques can demonstrate the fixation of a small amount of antibody in the presence of a large amount of background protein if the specific localization is at a higher local concentration. Counting is especially useful in following and quantitating the purification of either localizing antibody or the antigens involved in such localization, but has the disadvantage that the precise distribution on a cellular level is not possible, since only an average value for distribution of radioactivity over the sample measured is determined. The direct injection of fluorescein-labeled antibody has no merit since the amount which must be localized to be seen directly by fluorescence is larger than that required for detection by the fluorescein stain technique. Moreover, the fluorescein level causes nonspecific localization in the liver.