Immune system, genetics and regulation / edited by Eli E. Sercarz, Leonard A. Herzenberg, C. Fred Fox.

  • ICN-UCLA Symposium on the Immune System (1977 : Park City, Utah)
Date:
1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Immune system, genetics and regulation / edited by Eli E. Sercarz, Leonard A. Herzenberg, C. Fred Fox. Source: Wellcome Collection.

    699/792 (page 675)
    THE IMMUNE SYSTEM 675 Interestingly, when degranulating mast cells were labelled with cholera toxin, which has been shown to bind to the ganglio- side, GM^ (31), there was incre¿ised labelling in regions of fused membranes (32). This suggests that at least some of the glycolipids are not displaced during membrane fusion and that not all of the gangliosides are associated with protein. Bleb and whorl formation: Physiological or artifactual? (29) In regions of plasma and granule membrane interaction in degranulating mast cells, we sometimes observed multi-vesicu- lated membranous structures blebbing from the cell surface. These blebs were seen by thin section and freeze-fracture electron microscopy and were always unlabelled by the lectins and antibodies and were free of intramembrane particles. Although they were sometimes seen in unstimulated mast cells and in other cell types, they were much more frequent in de¬ granulating mast cells. They were usually seen overlying a]tered granules. Although blebs were not seen in regions where granule membranes were interacting with each other, multi¬ lamellar membrane whorls (myelin figures) were sometimes seen in these areas within cavities containing altered granules. Blebs and myelin figures have usually been considered fixation artifacts and we have been unable to exclude this possibility. On the other hand, they would provide the cell with a simple mechanism for disposing of excess lipid while conserving membrane proteins; in addition, the breaking off of blebs could be the mechanism by which the granules are opened to the extracellular space following membrane fusion, MAST CELL ACTIVATION: A PROPOSED SEQUENCE OF EVENTS It is very likely that the cross-linking of IgE receptors leads to the opening of gate Ca2+ channels in the mast cell membrane. In preliminary experiments we have not been able to demonstrate a relationship between IgE receptors and intra¬ membrane particles (33), and since an ion channel would be expected to have sufficient mass in the lipid bilayer to be visualised as an intramembrane particle in freeze-fracture studies (30), it seems unlikely that the Fc receptors are physically associated with the putative Ca^* channels. Thus, we would suggest that the Ca^^ channels open indirectly. Recently, we have shown that Con A, covalently linked to Sepharose 4B beads, induces Са^'''-dependent localised degranu- lation along the region of contact between the bead and adherent mast cells (34). This indicates that whatever the mechanism of Ca^^ channel opening is, it operates locally in the region of the cross-linked Fc receptors. The mechanism of Ca^*