Microwave antigen retrieval for immunocytochemistry on formalin-fixed, paraffin-embedded post-mortem CNS tissue

Microwave antigen retrieval methods were assessed for a panel of antibodies on formalin-fixed, paraffin-embedded sections from a range of human central nervous system (CNS) tissues taken at post-mortem. The immunoreactivity of a number of antigens (synaptophysin, PGP9.5, GFAP, carbonic anhydrase II, CD68, ferritin, HLA-DR, alpha beta-crystallin, measles and herpes viruses) was markedly enhanced by this procedure compared with other methods of antigen unmasking, such as trypsinization. Enhancement was noted both by an increased number of positive cells and by the intensity of reactions within individual cells and their processes. Furthermore, the microwave method produced uniform immunostaining over large surface area sections with no loss of morphological detail. Large cryostat sections of CNS tissue can be difficult to obtain with good morphology. The ability to retrieve a wide range of antigen in formalin-fixed, paraffin-embedded CNS tissue will greatly increase the range of investigations that can be carried out on this type of stored material.