Immunocytochemical localization of peroxisomal beta-oxidation enzymes in human fetal liver.

In the majority of congenital peroxisomal disorders, beta-oxidation of very long chain fatty acids is deficient. We have investigated the appearance and localization of the three peroxisomal beta-oxidation enzymes in normal fetal liver (fertilization age between 5 and 18 weeks) with protein A-gold immunocytochemistry and silver enhancement for light microscopic visualization. With specificity-tested polyclonal antibodies, acyl-CoA-oxidase, bifunctional enzyme, and 3-oxoacyl-CoA thiolase were localized in the peroxisomes of the parenchymal cells, which appear as brown or black granules. In the youngest specimen, no immunopositive reaction was obtained. A weak reaction with anti-thiolase was obtained at the age of 6-7 weeks. At a fertilization age of 8 weeks, peroxisomes could be distinctly visualized after immunostaining for all three enzymes. From a staining series with anti-thiolase on simultaneously treated slides, it appears that the amount of antigen per peroxisome and the organelle size increase between the seventh and eighteenth weeks. These data should enable a more specific diagnosis in fetal liver biopsies from pregnancies at risk and after termination of pregnancy.