Influence of fixatives on the immunoreactivity of paraffin sections

The unlabeled antibody peroxidase-antiperoxidase (PAP) technique was used to demonstrate IgA in paraffin sections of human tonsil fixed in eight commonly known fixatives. In all but one of the fixatives, treatment with trypsin prior to immunostaining resulted either in digestion of sections, or no change in positive staining. In tissues fixed in neutral buffered formalin-saline, positive staining was absent unless the sections had been treated with trypsin, and it has been shown that digestion requirements of different areas throughout a section may vary according to the effectiveness of fixation.