Localization of human chorionic gonadoptropin and placental lactogen by immunogold labeling for electron microscopy:...

To demonstrate human chorionic gonadotropin (hCG) and human placental lactogen (hPL) secretory granules in placenta and to illustrate newer embedding techniques and specific immunospecificity problems in the placenta, labeling experiments using immunogold or peroxidase combined with avidin-biotin enhancement in epoxy LX-112-, Araldite-, or LR gold-embedded tissue fixed in 2.5% glutaraldehyde or 2.5% paraformaldehyde were carried out in term and first-trimester normal human placenta and in partial hydatidiform moles. Increased sensitivity of the low-temperature LR gold method was found for hPL-labeled granules. beta hCG-labeled granules were noted in syncytium of first-trimester placenta, and beta hCG-containing granules in hydatidiform moles were similar to those of normal placenta. Paraformaldehyde fixation and LR gold embedding permitted identification of endoplasmic reticulum-associated labeling not observed with other methods. A brief review and discussion of immunolabeling methods, controls, and embedding materials is presented. We conclude that further refinement of peptide localization methods in the placenta is possible but must take into account the abundant potentially cross-reacting peptides present in the placenta.