Frozen Sections

Frozen sections are preferred for demonstration of antigens / enzymes which maybe lost during subsequent fixation and processing schedules. The freezing procedure is extremely important. If carried out too slowly it will result in the formation of ice crystal artifact, which may make histological interpretation very difficult. For optimum results tissue needs to be sliced thinly (maximum thickness 3 mm) and rapidly frozen in liquid nitrogen. Frozen sections are cut at a thickness of 5 µm using a cryostat. The sections are dried overnight at 37°C before fixation and subsequent staining or storage.

For subsequent immunocytochemical staining the sections are fixed in acetone for 20 minutes. It is important to dry the sections thoroughly, in order to optimize tissue morphology by reducing the effects of chromatolysis and membrane breakdown which is particularly evident with techniques involving long incubations in aqueous solutions.

Drying the sections overnight at 37°C does not affect section antigenicity. Frozen tissue can be stored in liquid nitrogen or at -70°C for many years without affecting antigenicity. The tissue should be wrapped in aluminum foil or immersed in embedding medium to prevent the tissue from drying out. Similarly, frozen sections can be wrapped in aluminum foil and stored at -20°C for a year or more without loss of antigenicity.