Immunoreactivity of some epitopes in longtime inappropriately stored paraffin-embedded tissues

One advantage associated with paraffin-embedded tissues is their availability for further studies and review. Where block filing facilities are not available, used blocks are often dumped in neglected rooms. This may affect their appropriateness for follow-up studies such as immunohistochemistry. The goal of this study was to perform immunohistochemical procedures on poorly stored paraffin-embedded blocks after a simple cleaning and re-embedding procedure. Thirty paraffin-embedded Onchocerca nodules, poorly stored for over 15 years, were used. The blocks were soaked overnight in tap water, rinsed in distilled water, air-dried, and re-embedded in fresh paraffin wax. Immunoperoxidase demonstrations of six major enzymes (LDH, SDHB, PDK2, G6PD, ME1, and A/BHD4) were performed on their sections and examined by light microscopy. Fifty-one 0.6% Female worm nodules in the amount of 51.6% had detectable SDHB, 56.6% had detectable levels of PDK2, 58.6% had A/BHD4, 61.1% had G6PD, 63.3% had detectable levels of ME1, and 64.5% had detectable levels of LDH. At a 99% confidence level, >= 30% of the nodules have all six enzymes detectable by immunohistochemistry and >= 35% have four detectable enzymes (LDH, PDK, A/BHD, and ME). Poorly stored archival formalin-fixed, paraffin-embedded Onchocerca nodules over a prolonged period still retain enough antigenicity for immunohistochemical demonstration of the enzymes LDH, SDHB, PDK2, G6PD, ME1, and A/BHD4 and perhaps other antigens.