Expression and modulation of FcepsilonRIalpha and FcepsilonRIbeta in human blood basophils.
BACKGROUND
The IgE receptor (FcepsilonRI) may exist as a tetramer (alphabetagamma2) or a trimer (alphagamma2) because FcepsilonRIbeta is dispensable for membrane expression of FcepsilonRIalpha. FcepsilonRIbeta amplifies signaling of FcepsilonRI so that regulation of FcepsilonRIalpha:beta stoichiometry would affect cellular responsiveness.


OBJECTIVE
We examined basophils from a variety of donors for differences in their expression of FcepsilonRIalpha and FcepsilonRIbeta protein.


METHODS
Enriched blood basophils were assessed at baseline and after IL-3 culture for FcepsilonRIalpha and FcepsilonRIbeta protein by Western blotting, surface FcepsilonRIalpha by flow cytometry, and FcepsilonRIbeta mRNA by real-time PCR. Basophil functional response was measured by allergen-triggered histamine release.


RESULTS
For the FcepsilonRIalpha subunit, 2 protein bands with molecular weights of 50 kd and 60 kd were identified by Western blots. The 60-kd band correlated to surface-expressed FcepsilonRIalpha detected by flow cytometry (Spearman R = 0.78, P <.01). Surface FcepsilonRIalpha also correlated with FcepsilonRIbeta protein (Spearman R = 0.92, P <.01). FcepsilonRIbeta protein levels increased disproportionately with higher surface FcepsilonRIalpha expression. The ratio of FcepsilonRIbeta to FcepsilonRIalpha varied 10-fold among donors and correlated with surface FcepsilonRIalpha. Basophil 50-kd alpha protein levels were similar despite a 10-fold range in surface FcepsilonRIalpha expression, implying stores of this protein such as those found in eosinophils. Unlike eosinophils, the basophil 50-kd protein was lost with culture and was absent from supernatants. Levels of beta protein and mRNA were enhanced by IL-3 culture, whereas FcepsilonRIalpha expression (by flow cytometry and 60 kd) was not.


CONCLUSIONS
These findings demonstrate variable stoichiometry of FcepsilonRIalpha:beta in whole cells and that this stoichiometry can be altered by IL-3 culture. With the assumption that all detected beta protein is surface expressed, these findings suggest a variable stoichiometry for FcepsilonRIalpha:beta that is also related to FcepsilonRIalpha surface expression.
Saini
S S
SS
Department of Medicine, Division of Clinical Immunology, Johns Hopkins University School of Medicine, Baltimore 21224, USA.
Richardson
J J
JJ
Wofsy
C
C
Lavens-Phillips
S
S
Bochner
B S
BS
Macglashan
D W
DW
D000328:Adult; D000818:Animals; D001491:Basophils / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D005434:Flow Cytometry / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects; D006636:Histamine Release; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D015471:Leukemia, Basophilic, Acute / Q000473:pathology; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D021122:Protein Subunits; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017455:Receptors, IgE / Q000097:blood* / Q000235:genetics; D014407:Tumor Cells, Cultured
D007377:Interleukin-3; D021122:Protein Subunits; D012333:RNA, Messenger; D017455:Receptors, IgE