Mechanism of formation of human IgE-binding factors (soluble CD23): III. Evidence for a receptor (Fc epsilon RII)-associated proteolytic activity.
There is mounting evidence that Fc epsilon RII (CD23) and its soluble fragments (IgE-binding factors [BFs] or soluble CD23) have pleiotropic activities. IgE-BFs are formed mainly by the proteolytic cleavage of surface Fc epsilon RII; they are first released as 37- and 33-kD unstable molecules that are subsequently transformed into 25-kD IgE-BFs. In this study, purified and radioiodinated 37-kD IgE-BFs as well as 45-kD Fc epsilon RII were used as substrates to identify the proteases leading to the formation of 25-kD IgE-BFs. These substrates generate 25-kD IgE-BFs when incubated with several Fc epsilon RII-bearing cells, including CHO1-7 cells (transfected with Fc epsilon RII cDNA); by contrast Fc epsilon RII- cells, including CHO control cells, have no effect. Highly purified unlabeled native 37-kD and recombinant 29-kD IgE-BFs also cleave labeled 45-kD Fc epsilon RII into 25-kD IgE-BFs. The proteolytic activity of these purified IgE-BFs is specifically removed by immunoprecipitation with an antibody against IgE-BFs. These data strongly suggest that Fc epsilon RII and some of its soluble fragments play an active role in the proteolytic mechanism generating IgE-BFs. They are supported by the observation that IgE-BFs released by CHO1-7 cells are cleaved exactly at the same sites as B cell-derived IgE-BFs. Taken collectively, the results are compatible with an autoproteolytic process.
Letellier
M
M
Laboratory for Allergy Research, Notre-Dame Hospital, University of Montreal, Quebec, Canada.
Nakajima
T
T
Pulido-Cejudo
G
G
Hofstetter
H
H
Delespesse
G
G
D000818:Animals; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D006801:Humans; D007073:Immunoglobulin E / Q000378:metabolism*; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000378:metabolism; D011961:Receptors, Fc / Q000302:isolation & purification / Q000378:metabolism*; D017455:Receptors, IgE
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D011961:Receptors, Fc; D017455:Receptors, IgE; D007073:Immunoglobulin E; D010447:Peptide Hydrolases