Structure and Function of Antigen Receptor Complexes on Murine B Lymphocytes

Abstract

B lymphocytes express immunoglobulin M (IgM) and D (IgD) on their surface that function as antigen receptors. When both Ig isotypes exist on one individual cell they possess the same antigen specificity. The binding of antigen to the receptors leads, together with other signals, to the activation of the cells. However, the mechanisms and structures by which Ig transmits such signals to the interior of the cells are unknown. One model of an antigen-recognition complex on the lymphocyte surface (Fig. 1) which is involved in the specific triggering of lymphocytes was postulated by us and others many years ago [5, 6]. By analogy with certain polypeptide hormones, this complex could consist of a recognition, a regulator and an effector element. Binding of antigen to the Ig molecule would induce its interaction with the regulator-effector complex which would then trigger a cascade of reactions that finally lead to the activation of the B cell. Since such receptor complexes have not yet been described, the aim of this work was to identify and biochemically characterize molecules which are associated and/or covalently linked to Ig. Furthermore, we are interested in the question whether IgM and IgD are linked to identical or different molecules.