title: IgM are associated to Sp alpha (CD5 antigen-like).
abstract: In 1993, we reported the presence of an IgM-associated peptide (M(r) 44 kDa; pI 5.45) in all immunoglobulin M (IgM) fractions purified from plasma/serum by various methods. This peptide was absent in Ig fractions of non-IgM isotypes. The N-terminal sequence was determined as being APPSGVRLVGGLH. To gain insight into the nature of this peptide, we further analyzed, using modern proteomic tools, the IgM-associated peptide isolated from cryoglobulins. Mass spectrometry revealed three peptides of different masses: 2203.13 (ELGCGAASGTPSGILYEPPAEK), 1564.83 (KPIWLSQMSCSGR), and 1544.77 (EATLQDCPSGPWGK). Theses sequences together with the already known N-terminal sequence allowed us to identity the IgM-associated peptide as Sp alpha (O43866 in TrEMBL database; CD5 antigen-like). Sp alpha is a member of the scavenger receptor cysteine-rich superfamily of proteins. This family includes the T-and B-cell antigens CD5 and CD6, and several of its members influence immune cell fate. Our finding may have important implications in the understanding of the homeostasis of IgM antibodies.
authors: Service Régional Vaudois de Transfusion Sanguine, Lausanne, Switzerland. jean-daniel.tissot@chuv.hospvd.ch
authors: Jean-Daniel
authors: JD
authors: Tissot
authors: Jean-Charles
authors: JC
authors: Sanchez
authors: Françoise
authors: F
authors: Vuadens
authors: Alexander
authors: A
authors: Scherl
authors: Jürg A
authors: JA
authors: Schifferli
authors: Denis F
authors: DF
authors: Hochstrasser
authors: Philippe
authors: P
authors: Schneider
authors: Michel A
authors: MA
authors: Duchosal
mesh_terms: D000595:Amino Acid Sequence; D018956:CD5 Antigens / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D007075:Immunoglobulin M / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data
chemical_list: D018956:CD5 Antigens; D007075:Immunoglobulin M