The intracellular localization of two antigens after uptake in vivo by peritoneal macrophages from normal mice.

Normal mouse macrophages, which had ingested ferritin labelled with fluorescein isothiocyanate and human serum albumin labelled with tetramethylrhodamine isothiocyanate , were fixed in formalin and embedded for electron microscopy. The examination of sections 1–2 μ thick and adjacent ultrathin sections showed that the yellow-green fluorescent droplets (due to ferritin-FITC) seen by fluorescence microscopy were in the same position as the ferritin-containing phagolysosomes as seen by electron microscopy. Normal mouse macrophages, which had ingested I-labelled human serum albumin ([I]HSA) and unlabelled ferritin, were investigated by electron microscopic autoradiography. Both antigens were found to be situated within the same lysosomes.