Characterization of residual bodies fromed in phase II cultivated human glia cells

Residual body-like structures have been shown to occur in small numbers in actively growing in vitro cultivated phase II human glia cells. In contact inhibited phase II glia cells they have been shown to accumulate. Whether such structures are analogous to lipofuscin pigment granules in post-mitotic cells in vivo has been uncertain. We have characterized such bodies in actively growing and contact inhibited cells as to their acid phosphatase content, heavy metal content, autofluorescent characteristics, staining characteristics and morphology. It has been shown that many of these bodies are acid phosphatase positive, contain heavy metals, show the natural and characteristic fluorescence of lipofuscin pigment, are PAS-positive, acid fast with Ziehl-Neelsen and are morphologically similar to lipofuscin. They are thus analogous to the lipofuscin granules found in post-mitotic cells in vivo. The number of such granules was found to increase following contact inhibition of the mitotic activity. We conclude that lipofuscin granules are found continuously in the culture and that the cellular content of these granules can be diluted by cell division.