Analysis of the endocytic pathway upon intracellular transport of IgG molecules through Fc receptors

The uniformly distributed Fc receptors (FcRs) on the surface of many cell t ypes are involved in a variety of immune reactions by non-specifically faci litating the entry of antigen-specific IgG molecules to the cell. Such reac tions may be beneficial to the organism when foreign antigens are involved, or harmful in cases of self antigens and viruses. In order to avoid the Ig G-mediated self antigen presentation or viral infection in autoimmunity and viral attack respectively, we attempt in this study to inhibit the intrace llular transport of antibodies. This blockage, however, implies: efficacy o f inhibition, inability of de novo exocytosis of the internalised antibody and finally maintenance of normal cell growth and morphology. We thus concentrate our interest on the endocytic pathway followed by a neu tralising antibody in murine trophoblast cells where we try to inhibit anti body intracellular transport by various agents according to the criteria se t above. In our model-system, IFN-gamma, upon induction of FcRs, facilitate s endocytosis of the anti-p21(ras) antibody which blocks in turn the IFN-ga mma-induced surface class II major histocompatibility complex (MHC) express ion. Using various intracellular transport inhibitors, we study the require d conditions by which these compounds cancel the inhibitory action of anti- p21(ras) and allow induction of class II MHC molecules by IFN-gamma. The ef fectiveness of the inhibitors in a ranking order is shown as following: mon odansyl cadaverine > didansyl cadaverine > pepstatin A > leupeptin > NH4Cl > brefeldin A > ZPCK > TPCK. From these inhibitors, only brefeldin A, leupe ptin, pepstatin and ZPCK do not allow exocytosis of the antibody in the cul ture medium and only didansyl cadaverine, pepstatin and leupeptin maintain cell viability and morphology. However, by sequential elimination based on this study's established criteria, only pepstatin A and leupeptin are shown to be effective inhibitors to specific antibody intracellular transport, p rotecting also the cell's viability and physiology.