While the term immunohistochemistry (IHC) is often used interchangeably with immunocytochemistry (ICC), significant differences exist between IHC and ICC in the nature of the biological sample that is analyzed.

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Sample Source

With IHC, tissues are removed from the patient or animal and either frozen or chemically preserved and embedded in paraffin. Sections as thin as 4μm are sliced from frozen or paraffin-embedded tissue and mounted onto slides in preparation for antibody-based staining. In this way, researchers can look at the localization of cellular components while maintaining the original architecture of the surrounding tissue, as shown in the right panel below.

For ICC, most, if not all, of the extracellular matrix and other stromal components are removed, leaving only whole cells to stain, as shown in the top image below. Sample sources for ICC can be from any suspension of cells, either from patients or animals (e.g., blood smears, swabs and aspirates) or tissue culture cell lines carried in a lab.

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Comparison of immunocytochemistry (ICC) and immunohistochemistry (IHC) staining. A549 human adenocarcinoma cells (top panel; ICC) and a human colon carcinoma tissue section (bottom panel; IHC) were fixed and stained for protein phosphatase 2 (PP2A) by indirect detection using Horseradish Peroxidase (HRP)-Conjugated Goat Anti-Mouse Secondary Antibody targeting the anti-PP2A primary antibody. Enzymatic development was completed using Pierce Metal-Enhanced DAB.

Sample Processing

Besides the biological source, IHC and ICC differ in the extent of sample processing required in preparation of antibody-mediated staining. ICC is associated with whole cells that have to be permeabilized, either through the fixation procedure or a separate permeabilization step, for the antibodies to reach intracellular targets. Depending on the thickness of the section and the method of fixation, IHC samples may not have to undergo a separate permeabilization step. IHC sections embedded in paraffin must be further processed prior to antibody staining, which can affect the ability of the antibodies to recognize target epitopes.

Once the samples are processed, there are few differences in the antibody staining protocol between IHC and ICC, although, as with all antibody-based staining, the protocol must be optimized based on the antibodies used.