Binding Antibodies to Tissue Sections Protocol Once tissues are fixed and permeabilized, the antibodies are added. These antibodies can be labeled directly or detected by a labeled secondary reagent. For indirect detection, any reagent that binds specifically to the primary antibody can be "tagged" and used to locate the antibody. The possible reagents include anti-immunoglobulin antibodies, protein A or G, or, if the first antibody is labeled with biotin, streptavidin. They can be labeled with enzymes or gold.
Labeling Antibodies with Biotin Protocol This protocol describes the covalent coupling of antibodies to biotin. Biotin groups bind with extremely high affinity to streptavidin and avidin, both of which are available commercially coupled with enzymes, fluorescent dyes, or iodine. A biotinylated primary antibody, therefore, can be detected with any of a wide variety of different labels. The biotinylation reaction is simple and mild, and rarely inactivates the antibody.
Labeling Antibodies with Fluorochromes Protocol Direct labeling of purified antibodies is the method of choice when simultaneously visualizing two or more antibodies of the same species, class, or subclass. This allows the localization of multiple antigens to be compared in the same cell, tissue, or sample. Labeled primary antibodies are also useful for improving background-to-readout ratios, and they can be essential for immunoassays in which good quantification is needed.
Labeling Antibodies with Iodine Protocol This protocol describes a simple chemical oxidation method for labeling antibodies with iodine. Iodide-125 (supplied as NaI) is oxidized to form iodine-125 (I2), which attacks tyrosyl and histidyl side chains. The iodinated antibodies are easily detected and quantitated using gamma counters or film. They are used primarily in immunoassays, but other techniques can be adapted conveniently to the iodine detection method.
Labeling Monoclonal Antibodies by Biosynthesis Protocol This method for tagging monoclonal antibodies involves growing hybridomas in the presence of radioactive amino acids. This protocol can be particularly useful when conventional labeling techniques cause the antibody to lose activity. The labeled antibodies that result are essentially identical to the unlabeled antibodies.