Immunoelectron microscopic localization of thyroglobulin in the human thyroid gland

The microidentification of the organelles containing thyroglobulin (TG) in the follicular cells of human thyroid glands were studied by the immunoelectron microscopic method. Fresh human thyroid glands were used for the purification of TG. TG was purified by differential salt fractionation and DEAE-cellulose chromatography. Anti-human TG rabbit IgG antibody was obtained by immunization of this purified TG. F(ab')2 fragments of anti-TG rabbit IgG antibody were prepared by pepsin digestion. The specificity of the antibody was tested on an Ouchterlony immunodiffusion plate. Conjugation of the purified F(ab')2 fragments of anti-TG rabbit IgG antibody to horse radish peroxidase was performed in order to use the direct peroxidase labelled antibody method. Under immunohistochemical light microscopy, the luminal colloid and the follicular cells appeared heavily stained. Under immunoelectron microscopy, positive reactions were observed in the rough endoplasmic reticulum, the Golgi apparatus, and the apical cell border. To date, no clear direct evidence of the presence of TG in the rough endoplasmic reticulum and the Golgi apparatus of human thyroid cells has ever been reported in immunoelectron microscopic studies. This study indicates that the use of F(ab')2 fragments of anti-TG rabbit IgG antibody in immunoelectron microscopic study is useful for the identification of TG in organelles of human thyroid follicular cells.