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Immunocytochemistry and Immunohistochemistry
Immunocytochemistry (ICC) and immunohistochemistry (IHC) are techniques that use antibodies to check for specific proteins or antigens in a sample. Th…
Immunocytochemistry or ICC and immunohistochemistry or IHC are staining techniques that use enzyme-linked antibodies to visualize and quantify specific proteins or antigens in cultured cells or tissue sections.
In ICC, a single layer of targeted cells is grown on a glass coverslip. The cells are fixed with a cross-linking agent to prevent enzymatic degradation of the antigen, then treated with a detergent to make the cell membrane permeable.
In IHC the whole tissue is fixed and embedded in a block of paraffin.Then, the sample is sectioned into thin slices, which can be placed on slides. Finally, the paraffin is removed to retrieve the antigen.
Once the antigens are accessible in the sample, they are bound by target-specific primary antibodies linked with conjugate enzymes like horseradish peroxidase.
The enzyme catalyzes the oxidation of DAB stain to a brown precipitate allowing visualization of the protein of interest.
If the signal detected is weak, secondary antibodies with conjugate enzymes are used to bind an unlabeled primary antibody on the target protein for further signal amplification.
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Q1: What is the difference between immunocytochemistry and immunohistochemistry?
Immunocytochemistry (ICC) visualizes proteins in cultured cells grown on glass coverslips, while immunohistochemistry (IHC) detects antigens in whole tissue sections. ICC uses single cell layers, whereas IHC requires tissue embedding in paraffin, sectioning into thin slices, and paraffin removal. Both techniques use antibodies to localize and quantify specific proteins or antigens.
Q2: How does sample preparation differ between ICC and IHC?
In ICC, cells are fixed with cross-linking agents and treated with detergent to permeabilize membranes. In IHC, tissue is fixed, embedded in paraffin wax, sectioned into thin slices, and the paraffin is removed to access antigens. Both methods prepare samples to allow antibodies to bind target proteins while preventing enzymatic degradation of antigens.
Q3: What role do primary and secondary antibodies play in these techniques?
Primary antibodies bind directly to target antigens. In direct methods, enzyme-conjugated primary antibodies generate signal immediately. In indirect methods, unlabeled primary antibodies are bound by enzyme-conjugated secondary antibodies, providing signal amplification. Secondary antibodies produce stronger signals than primary antibodies alone, improving detection sensitivity.
Q4: How does the enzyme-linked antibody system create a visible signal?
Conjugate enzymes like horseradish peroxidase catalyze oxidation of DAB stain into a brown precipitate, making the target protein visible. When signals are weak, secondary antibodies with conjugate enzymes amplify detection by binding unlabeled primary antibodies. This enzymatic reaction allows visualization of specific proteins under imaging biological samples with optical microscopy.
Q5: What are the two main detection methods used in ICC and IHC?
Colorimetric detection uses enzyme-conjugated antibodies that produce colored precipitates visible under optical microscopy. Fluorescence-based detection uses fluorophore-tagged antibodies that emit light under immunofluorescence microscopy. Both methods allow visualization of protein localization, with choice depending on sample type and available equipment.
Q6: Why is cell membrane permeability important in immunocytochemistry?
Detergent treatment makes cell membranes permeable, allowing antibodies to enter cells and access intracellular antigens. Without permeabilization, antibodies cannot penetrate the membrane to bind target proteins inside the cell. This step is essential for detecting cytoplasmic and nuclear antigens in ICC protocols.
Q7: What advantage does indirect immunostaining offer over direct methods?
Indirect methods use secondary antibodies that bind to primary antibodies, amplifying the signal and improving detection sensitivity. Multiple secondary antibodies can bind a single primary antibody, increasing enzyme or fluorophore concentration at the antigen site. This amplification makes indirect methods more sensitive for detecting low-abundance proteins or antigens.