Immunohistochemistry (IHC) is a standard lab technique for detection of protein within tissue, and IHC is still widely used in both research and diagnostic pathology. The evaluation of IHC staining is often semi-quantitative, introducing potential bias into interpretation of results. Many semi-quantitative approaches have been developed which incorporate both staining intensity and staining extent into final diagnosis 1-4. Other systems include scoring intensity and subcellular location in order to better localize expression 5. Incorporation of average scores from multiple viewers is often utilized in order to minimize the effects of single viewer bias 6. Despite these efforts, subjectivity in analysis still remains, particularly when evaluating the extent of staining 7. Protocol standardization and minimizing subjectivity from human input is paramount to creating accurate, reproducible IHC results.
There are other options besides IHC for determining protein expression within tissues. Within the research setting, immunohistochemistry has traditionally been viewed as a means to examine protein localization 8, while other techniques such as immunoblotting are viewed as gold standard for investigating protein expression. Determining tissue or cell compartment-specific expression is difficult without incorporating advanced techniques such as cell fractionation or laser capture microdissection 9,10. The use of fluorescent antibodies on tissue slides offers a reasonable compromise, but background autofluorescence due to NADPH, lipofuscins, reticular fibers, collagen, and elastin can make accurate quantitation difficult 11.
Automated computational pathology platforms are a promising direction for more objective quantitation of pathology staining 12-15. Combining multispectral imaging with tissue microarrays facilitates high-throughput analysis of protein expression in large sample sizes. With these techniques, analysis of protein co-localization, staining heterogeneity, and tissue and subcellular localization is possible while substantially reducing both inherent biases and time necessary for analysis, while returning data in a continuous rather than categorical format 16. Therefore, the purpose of this study was to demonstrate the utility of and methodology for performing multiplexed immunohistochemistry with analysis, using multispectral imaging software.
This protocol is written for manual, multiplex immunohistochemical staining of a single tissue section slide with four optimized monoclonal antibodies. As a representative experiment, nuclear anti-rabbit estrogen receptor alpha (ERα) and androgen receptor (AR) are multiplexed with membrane-bound anti-mouse CD147 and membrane-bound anti-mouse E-cadherin. Any antibody of choice may be substituted for the antibodies listed herein, but each combination of antibodies requires separate optimization. Pre-treatment for all the antibodies must be identical. The AR and CD147 antibodies should be optimized individually and then as a cocktail. Each antibody is detected using a biotin-free polymer system and one of 4 unique chromogens.