Friday, January 15, 2010
Can that brain you left in storage since 1996 still be assessed immunohistochemically?
The current issue of the Journal of Neuropathology and Experimental Neurology features an article about the effect of prolonged fixation time on the immunoreactivity of brain tissue being assessed for neurodegenerative disease. Dr. Irina Alafuzoff from Uppsula University in Sweden is the senior author on this study which looked at 20 post-mortem brains to determine whether prolonged fixation time has a deleterious effect on typical immunohistochemical stains used for neurodegenerative disease diagnosis. A panel of commercial antibodies to amyloid-[beta], ubiquitin, p62/sequestosome, tau, and [alpha]-synuclein was assessed using tissue microarray with several antigen retrieval methods. Short-term fixation was defined as a time period of up to 70 days before paraffin embedment. Long-term fixation was defined as 71 days to 14 years in formalin. The bottom line is that brains that are stored in 10% formalin for periods far exceeding a decade do indeed lose some immunoreactivity. But with proper antigen retrieval techniques (which are outlined in detail in the article) immunoreactivity can be maintained in these long-fixed tissues. Keep this article in mind to avoid false-negative results in brain autopsy specimens that have fixed for prolonged periods of time.
POSTSCRIPT: In an email to me regarding this article, Dr. Alafuzoff wanted to add this: "[A]s new antibodies are produced almost monthly and some of them work better than others on archived material (ex. synuclein), maybe we all working in this field should try out new antibodies at regular intervals."