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DIFFUSION ARTIFACTS IN 3,3'-DIAMINOBENZIDINE CYTOCHEMISTRY

throughout the cytoplasm (Figs. 2 and 3). The reaction product was seen as coarse masses of granules or accumulation of fine threads forming a mesh. The albumin-containing cells were scattered diffusely throughout the lobules. Most of cells situated in the centrilobular area contained a large amount of albumin. The control sections showed no staining. The localization of albumin in liver tissue observed is similar to that reported by using an immunofluorescent antibody method (5). In the lymph nodes of rabbits hyperimmunized with HPO, the cells containing antibody against HPO were mainly localized in the medullary cords adjacent to the lumen of the lymph sinuses or in the lumen itself (Fig. 4). The antibody-containing cells were classified into two types (Fig. 5). One is plasma cell, which had an eccentrically situated nucleus and contained a large amount of antibody throughout the cytoplasm. The other cell type contained only a small amount of antibody in the thin rim of cytoplasm. These cells, round in shape and small in size, may be interpreted as lymphoblasts or lymphoplasmacytes (2). In the intercellular space, there were often small granules of the reaction product. Since the reaction product was observed only occasionally in the intercellular space in sections not exposed to HPO prior to incubation with substrate for peroxidase, most of intercellular reaction product was thought to indicate the localization of antibody in this space. There were few antibody-containing cells in the germinal center. These results are also identical with those reported with frozen or paraffin sections (9). Our results indicate that fixation, dehydration and embedding employed do not disturb the antigen-antibody reaction. Furthermore, GMA sect ions gave clearer localization of the antigen and antibody at both the cytologic and histologic level than frozen or paraffin sections. Several tissue antigens were localized immunocytochemically by Nakane (8) by using methacrylate-embedded or Epon-embedded ultrathin sections and by partially removing the embedding medium. The embedding medium is difficult to remove from thin sections, however. The use of GMA as embedding medium is expected to simplify the procedure because of the dispensability of the removal of embedding medium. REFERENCES