Characteristics of the tissue section that influence the staining outcome in immunohistochemistry.

Immunohistochemistry (IHC) is influenced by several factors such as cold ischemia time, fixative, fixation time, paraffin, storage time, antibody, antigen retrieval technique and detection systems. In the setting of post-mortem tissue, not only post-mortem delay, but also agonal state is of interest. Here, we assessed an additional variable, i.e., the thickness of the section, and noted that this variable also influenced the IHC outcome. This is of significance when the extent of labelling is a parameter to be assessed, for example when assigning a stage or grade of a disease. Furthermore, when assessing brain tissue with neurons, soma measuring from 4 to 100 µm, various cellular compartments composed of different proteins are localised in sections measuring 4 or 7 µm. Thus, what is seen in a 7-µm-thick section might be lacking in a 4-µm-thick section. Lack of information regarding the molecular size of commercial antibodies is also disturbing as this parameter might influence the distribution of the molecule in the three-dimensional section. The choice of antibody to be used and the staining methodology have been acknowledged being of significance for IHC outcome; however, neither sections thickness or the molecular weight has been discussed sufficiently. IHC has been shown to be an unpredictable technique used for assessment of tissue. This emphasises the need for detailed methodological descriptions in publications, the need to acknowledge and to harmonize all eventual pitfalls related to this methodology.