Cellular and subcellular immunolocalization of alpha1-fetoprotein and albumin in rat liver. Reevaluation of various experimental conditions.

Open Access
Publisher Website
Google Scholar
Abstract
The cellular and subcellular immunolocalization of .alpha.1-fetoprotein (AFP) and albumin in rat liver was reevaluated. Some experimental conditions cause important immunolocalization artifacts. None of the tissue processing techniques tested resulted in release of large amounts of intracellular proteins into the fixative medium. Considerable diffusion of serum proteins into the cells occurred when frozen sections were prepared before fixation, or if tissues were fixed in alcohol-acetic acid under stirring. This was established by light microscopic immunolocalization of intracellular immunoglobulins, and by EM demonstration of their diffuse distribution in the cytoplasm and their absence from endoplasmic reticulum and Golgi apparatus lumina. The diffusion of serum proteins was minimized when a 24 h alcohol-acetic acid fixation, or a 6-8 h 10% paraformaldehyde fixation, each without stirring, were employed. The specificity of the reactions was further improved by perfusion-washing before fixation. During the neonatal period, only a fraction of the hepatocytes contained albumin or AFP; some cells were positive for both proteins. AFP and albumin were distributed in the rough and smooth endoplasmic reticulum and in the Golgi apparatus. In 3''-MDAB [3-methyl-4-dimethylaminoazobenzene] fed rats, at the early AFP induction stage, AFP was detected only in transitional cells; albumin was present in typical hepatocytes and some transitional cells. The importance of careful selection of experimental conditions for immunolocalization studies on exportable liver proteins was stressed. The hepatocytes may be functionally homogeneous in regard to AFP and albumin production. AFP may follow the secretion scheme generally recognized for liver export proteins.