Effect of ribonuclease A and deoxyribonuclease I on immunostaining of Ki-67 in fixed-embedded sections

Immunostaining of the cell cycle-associated Ki-67 antigen was studied on routinely formalin-fixed and paraffin-embedded tissue sections, using the Ki-67-specific monoclonal antibody MIB-1. Immunomorphological analysis of the Ki-67 immunostaining pattern was carried out following tissue pre-treatments including combinations of microwave heating and trypsinization, as well as of ribonuclease and deoxyribonuclease pre-digestion of the sections. The nucleolar Ki-67 immunostaining after slide pre-treatment by microwave heating followed by trypsinization was reduced only by ribonuclease pre-digestion, if this latter was used before heating. Ki-67 immunostaining was not significantly reduced by deoxyribonuclease treatment. We conclude that Ki-67, located in the nucleoli, may be associated there with nucleolar RNA.