Intensification of the immunocytochemical reaction by staining both sides of tissue sections.

We describe how the efficiency of immunostaining may be increased by staining paraffin sections on both sides. This modification exposes more antigenic binding sites per unit tissue area, as shown by the peroxidase-antiperoxidase and the avidin-biotin-peroxidase complex methods. Using antigen-rich tissue samples, the modified procedure made it possible to use more dilute primary antiserum or to reduce the incubation time of the tissue with the primary antibody. Alternatively, in tissue samples with sparse antigenic sites, the procedure made it possible to visualize and document very weak immunoreactivities.