Effect of heat-induced antigen retrieval following inconsistent formalin fixation.

The variable effects that inconsistent lengths of formalin fixation are known to have on the reactivity of tissue antigens were addressed by the application of a method for their heat-induced retrieval. Uniformly sized blocks of tonsil were fixed for increasing periods within 12 hours to 8 days before the heat retrieval and immunostaining of 30 tonsil antigens. The results were compared with their staining in the absence of heat retrieval, after prolongation of the standard retrieval time, and by use of a higher retrieval temperature. Consistent optimal staining of 26 of the 30 antigens was achieved despite the variable length of fixation. It is anticipated that the results will make a useful contribution to ongoing efforts toward the standardization of immunohistochemistry.