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The alternatively spliced CD64 transcript FcgammaRIb2 does not specify a surface-expressed isoform
M J van Vugt1, E Reefman, I Zeelenberg
1Department of Immunology, University Hospital Utrecht, The Netherlands.
European Journal of Immunology
|February 5, 1999
Summary
The hFcgammaRIb2 transcript does not encode a surface-expressed CD64 isoform on myeloid cells. This finding suggests other Fc receptor transcripts may also not represent distinct isoforms.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Class I human IgG receptor (CD64) has three homologous genes (A, B, C) and six identified transcripts.
- The hFcgammaRIa1 isoform encodes the high-affinity IgG receptor.
- The hFcgammaRIb2 transcript was proposed as a second surface-expressed CD64 isoform on myeloid cells.
Purpose of the Study:
- To investigate the proposed role of the hFcgammaRIb2 transcript as a surface-expressed CD64 isoform.
- To determine if hFcgammaRIb2 is expressed on the plasma membrane of myeloid cells.
Main Methods:
- Transfection of tagged hFcgammaRIb2 (hFcgammaRIb2tag) and FcR gamma-chain into IIA1.6 cells.
- Detection of hFcgammaRIb2tag transcript and protein using tag-specific monoclonal antibodies.
- Confocal scan laser microscopy to assess protein localization.
Main Results:
- Both hFcgammaRIb2tag transcript and protein were present in transfected cells.
- No surface expression of hFcgammaRIb2tag was detected.
- Confocal microscopy showed hFcgammaRIb2tag retained in the endoplasmic reticulum, not reaching the plasma membrane.
Conclusions:
- hFcgammaRIb2 is not surface-expressed and does not represent a distinct CD64 isoform.
- This challenges the validity of other Fc receptor transcripts as functional isoforms.
- Further research is needed to clarify the roles of various Fc receptor transcripts.