Formic acid antigen retrieval is used with paraffin embedded, formalin or paraformaldehyde-fixed tissues. When tissues are fixed in cross-linking agents such as paraformaldehyde, these agents will covalently cross-linked proteins, resulting a reduction in the available epitopes for antibody binding. The result is weak or negligible levels of protein detection. Consequently, the use of an acidic agent has been shown to greatly improve detection of some proteins; formic acid is typically used for the detection of amyloid plaque deposits associated with Alzheimer’s disease. However, not all antibodies respond equally well to a low pH solution treatment, and several antigen retrieval condition should be tested when optimizing stainng conditions.
Formic Acid Solution (10%)
- Prepare the solution by adding 10 ml of 99% formic acid to 90 ml of distilled water. Be sure to mix the solution well; the pH should be in the range of 1.6-2.0.
- Deparaffinize and rehydrate tissue sections.
- Incubate sections using the 10% formic acid solution solution for 10 to 20 minutes at room temperature. A range of incubation times (suggestion 10, 15, and 20 minutes) should be tested to determine an optimal antigen retrieval time.
- Rinse sections in two changes of a buffered solution, such as PBS or TBS, in order to neutralize acidity.
- Proceed with the tissue blocking for immunohistochemistry.