Antibody penetration into LR-White sections.

The purpose of this investigation is to study the ability of antibodies to penetrate sections of LR-WHITE resin. The methods used in this study were the following: (1) Reembedding of sections labeled with immunogold (1 nm) and peroxidase/DAB/gold chloride, (2) tilting of ultrathin sections treated with immunogold (1 nm), (3) immunolabeling of cylindrical structures embedded in LR-WHITE, (4) application of primary and secondary antibodies on opposite sides of ultrathin sections. Fibrin and human pituitary tissue was embedded in LR-WHITE and treated with anti-fibrinogen or anti-ACTH respectively (ACTH = Adrenocorticotropic hormone). No indication of antibody penetration into the section were found with either of the methods, contrary to findings in earlier publications. The significance of this result is that antigens cannot be demonstrated in the interior of LR-WHITE sections with post-embedding techniques. Furthermore, LR-WHITE resin may be used for quantitative immunoelectron microscopy, and the resin may be used for double immunogold labeling since the application of immunoreagents on opposite sides of the sections is completely safe.