On the origin of the FcRIII (CD16)-containing vesicle population in human neutrophil granulocytes.
Human blood neutrophils bear two types of Fc receptors that recognize the Fc portion of immunoglobulin G: FcRII and FcRIII. In earlier studies we found that neutrophils not only express FcRIII on their plasma membrane but also contain a large population of FcRIII-containing vesicles mainly located in the juxtanuclear area. To find out whether these vesicles derive from the plasma membrane, we used electron microscopic techniques to study compartments involved in ligand-independent endocytosis in human neutrophil granulocytes. The endocytic compartments were labeled with BSA-gold. This marker entered the cell through non-coated invaginations of the plasma membrane as well as via coated pits. After internalization, BSA-gold was present in numerous electron-lucent vesicles in the juxtanuclear area and in the trans-Golgi reticulum, endosomes, and lysosome-like structures. FcRIII also occurred in the BSA-gold-containing electron-lucent vesicles in the juxtanuclear area, as shown by postembedding immunocytochemical labeling of FcRIII in cells already containing BSA-gold. Quantification showed that 29% of all FcRIII-containing vesicles also bear BSA-gold while the remaining 71% contain only the receptor. In sum, our findings show that one third of the FcRIII-containing electron-lucent vesicles in neutrophil granulocytes derive from the plasma membrane and are involved in ligand-independent endocytosis of FcRIII. The majority of these vesicles, however, are not of an endocytic origin and might constitute an "internal pool" of receptors in these cells.
Jost
C R
CR
Laboratory for Electron Microscopy, University of Leiden, The Netherlands.
de Goede
R
R
Fransen
J A
JA
Daha
M R
MR
Ginsel
L A
LA
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000378:metabolism*; D004705:Endocytosis; D011992:Endosomes / Q000276:immunology* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000276:immunology / Q000648:ultrastructure; D006801:Humans; D008247:Lysosomes / Q000276:immunology / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D009504:Neutrophils / Q000276:immunology* / Q000648:ultrastructure; D011961:Receptors, Fc / Q000378:metabolism*; D017452:Receptors, IgG; D014617:Vacuoles / Q000276:immunology / Q000648:ultrastructure
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D011961:Receptors, Fc; D017452:Receptors, IgG