Microwaving and Fluorophore-Tyramide for Multiplex Immunostaining on Mouse Adrenals − Using Unconjugated Primary Antibodies from the Same Host Species

Immunostaining is widely used in biomedical research to show the cellular expression pattern of a given protein. Multiplex immunostaining allows labeling using multiple primary antibodies. To minimize antibody cross-reactivity, multiplex immunostaining using indirect staining requires unlabeled primary antibodies from different host species. However, the appropriate combination of different species antibodies is not always available. Here, we describe a method of using unlabeled primary antibodies from the same host species (e.g., in this case both antibodies are from rabbit) for multiplex immunofluorescence on formalin-fixed paraffin-embedded (FFPE) mouse adrenal sections. This method uses the same procedure and reagents used in the antigen retrieval step to strip the activity of the previously stained primary antibody complex. Slides were stained with the first primary antibody using a general immunostaining protocol followed by a binding step with a biotinylated secondary antibody. Then, an avidin-biotin-peroxidase signal development method was used with fluorophore-tyramide as the substrate. The immunoactivity of the first primary antibody complex was stripped through immersion in a microwaved boiling sodium citrate solution for 8 min. The insoluble fluorophore-tyramide deposition remained on the sample, which allowed the slide to be stained with other primary antibodies. Although this method eliminates most false positive signals, some background from antibody cross-reactivity may remain. If the samples are enriched with endogenous biotin, a peroxidase-conjugated secondary antibody may be used to replace the biotinylated secondary antibody to avoid the false positive from recovered endogenous biotin.