Ultrastructural distribution of interferon receptor sites on mouse L fibroblasts grown in suspension: ganglioside blockade of ligand binding

Abstract

Murine beta-interferon (IFN) receptors on L929 cells grown in suspension culture were visualized by indirect immunoferritin electron microscopy. Ferritin label on these cells was associated primarily with the coated areas and coated pits of the membrane, in contrast to previous observations with L929 cells grown in a monolayer, which did not reveal such coated areas or pits but showed ferritin label distributed randomly on the cell membrane (Kushnaryov et al., Infect. Immun. 36:811-821, 1982). On about 15% of the cell sections from suspension-grown cells, the ferritin label was found outside coated membrane areas. These findings suggest that different cell populations exist with respect to the localization and possibly the affinity of IFN receptors. In the same experiment, exogenously added gangliosides blocked the binding to cell surfaces not only of 125I-labeled IFN but also of unlabeled IFN as revealed by an immunospecific ferritin labeling technique, providing direct evidence that gangliosides interfere with the binding of IFN to specific receptor sites on the surface of mouse L929 cells. These studies establish that the binding of IFN to cell membranes, depending on cell growth conditions, can involve coated areas and coated pits, to which certain hormones and toxins have been shown to bind.

Alpha/beta interferons fail to induce antiviral activity from within the nucleus

“…Electron microscopic observation of the fate of murine (Mu) IFN-W/p, as visualized by ferritin-labeled immunoglobulin G, has shown the presence of IFN in coated pits, coated vesicles, and receptosomes a few minutes after binding to mouse L-cell receptors (14), and human IFN-otA molecules labeled with colloidal gold for monitoring the endocytic pathway have been visualized successively on plasma membrane receptors, in clathrin-coated pits, in receptosomes inside the cell, and finally in lysosomes (17). Of particular interest are the observations that suggest the existence of IFN receptors within the cell nucleus.…”