The human Ig-beta cDNA sequence, a homologue of murine B29, is identical in B cell and plasma cell lines producing all the human Ig isotypes (original) (raw)
Related papers
Receptors for IgM on Human B Lymphocytes
Scandinavian Journal of Immunology, 1978
Using a rosette technique with IgM coated bovine red blood cells (EA-IgM) receptors for IgM can be demonstrated on human B-lymphocytes. While in the peripheral blood B cells with IgM receptors are found only occasionally, between 7 and 33%. mean 16%, of tonsil B-lymphocytes exhibit receptors for IgM. This was shown in double marker studies using EA-IgM for the demonstration of IgM receptors and fiuorochrome labelled conjugates for the demonstration of S-IgD. S-IgM and B cell antigens. These receptors are specific for IgM. they can be completely blocked by IgM-anti OVA complexes and partially by free IgM. but not at all by aggregated human IgG. They are sensitive to trypsin and pronase but reconstitute after further incubation at 37°C. These data show that not only T and CLL cells but also some normal B-lymphocytes have receptors for IgM. We favour the view that CLL lymphocytes may derive from these B-lymphocytes. which may represent a certain maturation step in B cell development.
A tyrosine-based signal present in Ig α mediates B cell receptor constitutive internalization
The Journal of Immunology
B lymphocytes express Ag receptors (BCR) that are composed of ligand binding subunits, the membrane Igs, associated with Ig alpha/Ig beta heterodimers. One main BCR function is to bind and to internalize Ags. Peptides generated from these internalized Ags may be presented to T lymphocytes. Here, we have analyzed the involvement of BCR Ig alpha/Ig beta components in BCR constitutive endocytosis. The role of Ig alpha subunit in BCR constitutive endocytosis was first determined in the context of an IgM-based BCR. In contrast with BCR that contain wild-type Ig alpha, surface BCR lacking Ig alpha cytoplasmic domain were not constitutively internalized. The respective roles of Ig alpha and Ig beta subunits were then analyzed by expressing chimeric molecules containing the cytoplasmic domains of either subunits in a B cell line. Only the Ig alpha cytoplasmic domain contained an internalization signal that allowed constitutive endocytosis of Ig alpha chimeras via coated pits and accumulatio...
Receptors for IgM on Certain Human B Lymphocytes
The Journal of Immunology
A receptor for IgM was demonstrated on the surface of human B lymphocytes by using a rosette technique with ox erythrocytes coated with rabbit IgM antibody (EAM). Lymphocytes forming rosettes with EAM did not bind sheep red cells, had membrane Ia-like antigens and, in some instances, surface immunoglobulin. The specificity of EAM rosettes was confirmed by inhibition experiments with purified human Ig. IgM but not IgG molecules inhibited the rosette reaction. In addition, inhibition of EAM rosettes with IgM fragments showed that the receptor has affinity for a part of the molecule located in the Fc portion. By analogy with the receptors previously found on certain human T cells, receptors for IgM were not detected on freshly isolated B cells, but were expressed after overnight culture in IgM-free media. Studies on different human lymphoid tissues showed that IgM receptors are expressed on a limited percentage of both circulating and noncirculating B cells. In addition to normal B cel...
Signal transduction by immunoglobulin is mediated through Ig alpha and Ig beta
Journal of Experimental Medicine, 1993
Immunoglobulin (Ig) antigen receptors are composed of a noncovalently-associated complex of Ig and two other proteins, Igo~ and Ig3. The cytoplasmic domain of both of these Ig associated proteins contains a consensus sequence that is shared with the signaling proteins of the T cell and Fc receptor. To test the idea that Igc~-IgB heterodimers are the signaling components of the Ig receptor, we have studied Ig mutations that interfere with signal transduction. We find that specific mutations in the transmembrane domain of Ig that inactivate Ca 2+ and phosphorylation responses also uncouple IgM from Igoe-Ig/3. These results define amino acid residues that are essential for the assembly of the Ig receptor. Further, receptor activity can be fully reconstituted in Ca 2+ flux and phosphorylation assays by fusing the cytoplasmic domain of Igct with the mutant Igs. In contrast, fusion of the cytoplasmic domain of Ig~ to the inactive Ig reconstitutes only Ca z+ responses. Thus, Igor and IgB are both necessary and sufficient to mediate signal transduction by the Ig receptor in B cells. In addition, our results suggest that IgoL and IgB can activate different signaling pathways.
Journal of Experimental Medicine, 1992
Snml'nal~ We have recently reported that on human B lymphocytes, membrane IgM (mlgM) associates with a heterodimer of 47-and 37-kD polypeptides, the 47-kD subunit being encoded by the rob-1 gene. We show here that expression of rob-l, both at the mRNA and the protein level, is not restricted to IgM + B cells but can also be found in IgM-pre-B cells and mlgM-IgG + B cells. Membrane forms of IgD and IgG, isolated from freshly isolated human B cells and B cell lines, are expressed together with heterodimeric protein structures biochemically similar to the mlgM-associated polypeptides, and these were shown to comprise the products of the rnb-1 and B29 genes, or homologous genes. Finally, all three classes of antigen receptors are linked to protein kinases, capable ofphosphorylating the Ig-associated heterodimers. Our findings provide insight in the structural organization of the different antigen receptors on human B cells and have implications for their function.