Stability of immunofluorescence reactions produced by polyclonal and monoclonal antibody conjugates for rabies virus

We investigated two consumer complaints that described fading of immunofluorescence reactions associated with the use of a commercial antirabies, fluorescein-labeled, monoclonal antibody conjugate. We compared the performance of this product with that of two polyclonal antibody antirabies conjugates and observed significant diminution of fluorescence with the monoclonal antibody conjugate only. Furthermore, the fading occurred only on tissue impressions that had been mounted but not exposed to UV light excitation, thereby essentially eliminating the photobleaching associated with fluorescence microscopy as a causative factor. Our observations suggest that mounting medium pH and the holding temperature of stained slides may be critical factors in maintaining optimal immunofluorescence reactions with this monoclonal antibody conjugate. We discuss some probable mechanisms that could produce the type of fading observed and also suggest certain precautionary measures for use with this monoclonal antibody conjugate.