cDNA cloning of the B cell membrane protein CD22: a mediator of B-B cell interactions.
We have cloned a full-length cDNA for the B cell membrane protein CD22, which is referred to as B lymphocyte cell adhesion molecule (BL-CAM). Using subtractive hybridization techniques, several B lymphocyte-specific cDNAs were isolated. Northern blot analysis with one of the clones, clone 66, revealed expression in normal activated B cells and a variety of B cell lines, but not in normal activated T cells, T cell lines, Hela cells, or several tissues, including brain and placenta. One major transcript of approximately 3.3 kb was found in B cells although several smaller transcripts were also present in low amounts (approximately 2.6, 2.3, and 1.6 kb). Sequence analysis of a full-length cDNA clone revealed an open reading frame of 2,541 bases coding for a predicted protein of 847 amino acids with a molecular mass of 95 kD. The BL-CAM cDNA is nearly identical to a recently isolated cDNA clone for CD22, with the exception of an additional 531 bases in the coding region of BL-CAM. BL-CAM has a predicted transmembrane spanning region and a 140-amino acid intracytoplasmic domain. Search of the National Biological Research Foundation protein database revealed that this protein is a member of the immunoglobulin super family and that it had significant homology with three homotypic cell adhesion proteins: carcinoembryonic antigen (29% identity over 460 amino acids), myelin-associated glycoprotein (27% identity over 425 amino acids), and neural cell adhesion molecule (21.5% over 274 amino acids). Northern blot analysis revealed low-level BL-CAM mRNA expression in unactivated tonsillar B cells, which was rapidly increased after B cell activation with Staphylococcus aureus Cowan strain 1 and phorbol myristate acetate, but not by various cytokines, including interleukin 4 (IL-4), IL-6, and gamma interferon. In situ hybridization with an antisense BL-CAM RNA probe revealed expression in B cell-rich areas in tonsil and lymph node, although the most striking hybridization was in the germinal centers. COS cells transfected with a BL-CAM expression vector were immunofluorescently stained positively with two different CD22 antibodies, each of which recognizes a different epitope. Additionally, both normal tonsil B cells and a B cell line were found to adhere to COS transfected with BL-CAM in the sense but not the antisense direction.(ABSTRACT TRUNCATED AT 400 WORDS)
Wilson
G L
GL
Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Fox
C H
CH
Fauci
A S
AS
Kehrl
J H
JH
D000293:Adolescent; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000096:biosynthesis / Q000235:genetics*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis / Q000235:genetics*; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000235:genetics*; D002648:Child; D002675:Child, Preschool; D003001:Cloning, Molecular; D006801:Humans; D037102:Lectins; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins / Q000096:biosynthesis; D051918:Sialic Acid Binding Ig-like Lectin 2
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; D015815:Cell Adhesion Molecules; D037102:Lectins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2