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Attachment of the antigen receptor to the B cell membrane
Immunochemistry
Models for the attachment of antigen receptors to the B cell membrane and some of the issues which arise on a consideration of this problem are discussed with reference to IgM receptors. It is suggested that the binding to the membrane may be a consequence of a unique structural feature of receptor immunoglobulin. Alternatively this may be a result of the subcellular site of biosynthesis of the receptor or the presence of a specific proreceptor molecule. Experiments to differentiate between the models are briefly discussed.
Scandinavian Journal of Immunology, 1991
We do not agree with the analysis of Langman and Cohn on the function of Ig receptors. We have reviewed the available literature regarding anti-Ig activation of B cells and found it contradictory and unconvincing. We have presented experimental evidence on the inability of Ig receptors on B cells to mediate activation or tolerogenic signals. We suggest that the Ig receptors serve to focus antigen to specific B cells so the B cells can be activated by TI antigens or helper T cells. The Ig molecules also bind foreign antigen and thereby initiate internalization and antigen processing. The processed peptides are exported to the membrane, where they associate with MHC class II antigens, thus transforming B cells into efficient antigen-presenting cells.
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...
Stability of the B cell antigen receptor complex
Molecular Immunology, 2000
The B cell antigen receptor (BCR) comprises the membrane-bound immunoglobulin (mIg) molecule and the Ig-a/Ig-b heterodimer. By comparing the stability of the IgD-BCR and IgM-BCR in dierent detergent lysates, we ®nd that the IgD-BCR is more stable than the IgM-BCR. Analysis of chimeric mIgD molecules suggests that the dm transmembrane region is responsible for the more stable association of mIgD with the Ig-a/Ig-b heterodimer. Further, the dierential glycosylation of Iga molecules, in the two dierent BCR complexes, is determined solely by the ectodomains of the mIg molecules. The implications of these ®ndings for the intracellular transport and the signalling capacity of the BCRs are discussed.
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.
Journal of Experimental Medicine, 1970
High-rate antibody-forming cells and immunological memory cells can be selectively retained if filtered through a column coated with relevant antigen. This trapping can be blocked if the cells are incubated with an anti-immunoglobulin serum prior to column passage. A similar blocking is not observed when cells are treated with an anti-lymphocyte serum, thereby excluding the possibility that any antibodies combining with surface structures could cause this effect. By the use of antisera specific for heavy or light chain antigens, it was possible to locate such antigens in the antigen-binding receptor areas of immune cells. Criss-cross studies using antisera specific for gamma 1 or gamma 2a heavy chains showed that the membrane receptor has the same heavy chain as will be present in the eventual product of that cell, the humoral antibody.