Expression sites of immunohistochemistry markers in oral diseases - A scoping review

Introduction: Immunohistochemistry (IHC) has not always been an easy field for the research beginners like postgraduates, research fellows and scientists. Meaningful interpretation of IHC positivity needs expertise. This could be made easier for beginners by developing a conceptual framework of markers. The literature review revealed a lack of qualitative evidence on the hitherto IHC studies on oral diseases about the overall expression of IHC markers and its comparison with pathology and normal tissues. Aim: This scoping review aimed to examine the literature and classify the various immunohistochemistry markers of oral diseases based on the tissue, cell and site of expression. Materials and Methods: The review was in accordance with Preferred Reporting Items for scoping reviews (PRISMA -ScR). Electronic databases such as PubMed and Cochrane were searched for relevant articles till 2021. Results: We included 43 articles. We found five different possibilities of the site of expression of a marker in a cell. They are the nucleus, cytoplasm, cell membrane, extracellular matrix or any of the above combinations. Based on the tissue of expression, we also mapped the markers expressed in oral diseases to their tissue of origin as ectoderm, endoderm, mesoderm and markers with multiple tissues of expression. Based on our results, we derived two classifications that give an overview of the expression of IHC markers in oral diseases. Conclusion: This scoping review derived new insight into the classification of IHC markers based on cell lineage, tissue and site of expression. This would enable a beginner to better understand a marker with its application and the interpretation of the staining in research. This could also serve as a beginner's guide for any researcher to thrive and explore the IHC world.