PrP immunohistochemistry: Different protocols, including a procedure for long formalin fixation, and a proposed schematic classification for depositsin sporadic Creutzfeldt-Jakob disease

The use of immunohistochemistry on formalin-fixed and paraffin-embedded tis sue has greatly improved the neuropathological diagnosis of Creutzfeldt-Jak ob disease and the other subacute spongiform encephalopathies in human and animals. Two pitfalls of this technique, however, currently exist: low sens itivity after long formalin fixation and difficulties in interpreting some images. Here we review the protocols currently in use for the pretreatment of sections allowing PrP detection by immunohistochemistry. In addition, a technique useful after long formalin fixation is reported: enzymatic digest ion with proteinase K (24 degrees C, 1/100 for 8 minutes) was employed in a ddition to the usual autoclaving (121 degrees C for 10 minutes) followed by formic acid (99% for 5 minutes) and 4M guanidine thiocyanate (4 degrees C for 2 hours). This allowed a substantial increase in the sensitivity of 3F4 immunohistochemistry on paraffin-embedded tissue, especially after prolong ed formalin fixation. In addition, we suggest a simple method for classific ation of PrP immunolabelling in sporadic Creutzfeldt-Jakob disease that wou ld allow easy comparisons. (C) 2000 Wiley-Liss. Inc.