Difference in CD22 molecules in human B cells and basophils.
OBJECTIVE
CD22 is believed to be restricted to normal and neoplastic B cells. Human basophils were found to express CD22 molecules. Among the antibodies against CD22, Leu14, which recognized the ligand binding domain, reacted to basophils, and B3 and 4KB128, which recognized the amino terminus side and carboxy terminus side of the ligand binding epitope, respectively, did not. To clarify the difference of CD22 antigenicity in human B cells and basophils, we investigated RNA sequence and structures of CD22 molecules.


METHODS
Purified B cells and basophils were obtained from normal human volunteers by using a MACS magnetic cell sorting system and anti-CD19 and anti-Fc epsilon R1 antibodies, respectively. RT-PCR and sequencing of CD22 mRNA were performed in the exons 3 to 8. Western blotting analysis of CD22 was also performed.


RESULTS
The sequence of CD22 mRNA extracted from the basophils was the same as that of B cells in exons 3 to 8 (epitopes recognized by Leu14, B3, and 4KB128 were translated from exons 4 and 5). Reduced CD22 peptide extracted from the basophils reacted to Leu14 as well as B3 and 4KB128, and the molecular size of the reduced and nonreduced products was 130 kDa as expected.


CONCLUSIONS
Disulfide bonds and the resulting 3D conformation of the CD22 molecules may have important roles in the difference of antigenicity of CD22 beta in B cells (CD22 beta 1) and basophils (CD22 beta 2). The difference in molecular structure surrounding the ligand-binding domain of CD22 may imply a specialization of the conformational forms of CD22 according to the ligand isoforms.
Toba
Ken
K
First Department of Internal Medicine, Niigata University Hospital, Niigata City, Japan. tobaken@med.niigata-u.ac.jp
Hanawa
Haruo
H
Fuse
Ichiro
I
Sakaue
Minori
M
Watanabe
Kenichi
K
Uesugi
Yumiko
Y
Higuchi
Wataru
W
Takahashi
Masuhiro
M
Aizawa
Yoshifusa
Y
D000328:Adult; D000906:Antibodies; D000941:Antigens / Q000276:immunology*; D015703:Antigens, CD / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D018941:Antigens, CD19 / Q000276:immunology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D001491:Basophils / Q000276:immunology*; D015153:Blotting, Western; D015815:Cell Adhesion Molecules; D002469:Cell Separation / Q000379:methods; D004220:Disulfides / Q000737:chemistry; D005091:Exons; D006801:Humans; D037102:Lectins; D008280:Magnetics; D008297:Male; D011487:Protein Conformation; D012333:RNA, Messenger / Q000097:blood / Q000737:chemistry; D017455:Receptors, IgE / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017423:Sequence Analysis, RNA; D051918:Sialic Acid Binding Ig-like Lectin 2
D000906:Antibodies; D000941:Antigens; D015703:Antigens, CD; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; D015815:Cell Adhesion Molecules; D004220:Disulfides; D037102:Lectins; D012333:RNA, Messenger; D017455:Receptors, IgE; D051918:Sialic Acid Binding Ig-like Lectin 2