Commentary on “Antigen Retrieval Immunohistochemistry: Past,Present,and Future”

Almost half a century has passed from the first successful application of peroxidase labeled antibodies to routinely processed formalin-fixed paraffin-embedded (FFPE) tissues with the express purpose of improved diagnosis. Retention of the morphological features that are the foundation of surgical pathology was key to rendering the “immunoperoxidase” method attractive for diagnostic use. However, significant obstacles remained, including the limited number of antibodies that “worked” on FFPE tissues, the relatively low sensitivity of detection methods, and, most important in terms of broad utility, the deleterious effects of formalin fixation on many antigens. There were advances, some dramatic, but overall progress was slow. ¹ The advent of the hybridoma technique was eventually to lead to the generation of numerous monoclonal antibodies that were rapidly incorporated into immunohistochemistry. Concurrently, detection systems improved, and attempts were made to “undo” the effects of formalin fixation by enzymatic digestion, with limited success.

Against this background, the introduction of what now is known as “antigen retrieval” (AR), or by some as heat induced epitope retrieval (HIER), provided huge impetus to the field, having the effect of greatly increasing the number of antigens that were demonstrable in FFPE tissues, including many with diagnostic application. This advance was entirely counterintuitive and was based upon exhaustive research in dusty libraries (no Internet searches!). There evidence was found that the “antigenic potency” of tetanus toxoid, toxin that had been inactivated by formalin, could in large part be restored by something as simple as boiling. Why not apply the same approach to FFPE tissues?

The current issue of the Journal of Histochemistry & Cytochemistry has selected as its Classical Article a paper by Shan-Rong Shi, Richard Cote, and Clive Taylor that describes the evolution of the AR method, and the impact of AR in diagnostic pathology and broader fields of research, as measured just 5 years after its introduction. That this initial promise has been fulfilled manyfold is attested by extensive day-to-day use of AR in histochemistry laboratories worldwide, and by an enormous ever expanding literature, even providing the basis for DNA extraction methods that underpin much of diagnostic molecular and genetic testing as performed upon archival tissues, which mostly are what we have at our time of need.^1,2