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.
Laboratory for Electron Microscopy, University of Leiden, The Netherlands.
C R
CR
Jost
R
R
de Goede
J A
JA
Fransen
M R
MR
Daha
L A
LA
Ginsel
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