ABSTRACT
Receptor editing in the bone marrow (BM) serves to modify the Ag receptor specificity of immature self-reactive B cells, while anergy functionally silences self-reactive clones. Here, we demonstrate that anergic B cells in hen egg lysozyme Ig (HEL-Ig)/soluble HEL double transgenic mice show evidence of having undergone receptor editing in vivo, as demonstrated by the presence of elevated levels of endogenous kappa light chain rearrangements in the BM and spleen. In an in vitro IL-7-driven BM culture system, HEL-Ig BM B cells grown in the presence of soluble HEL down-regulated surface IgM expression and also showed induction of new endogenous kappa light chain rearrangements. Using a panel of soluble protein ligands with reduced affinity for the HEL-Ig receptor, the editing response was shown to correlate in a dose-dependent fashion with the strength of signaling through the B cell receptor. The finding that the level of B cell receptor cross-linking sufficient to induce anergy in B cells is also capable of engaging the machinery required for receptor editing suggests an intimate relationship between these two mechanisms in maintaining B cell tolerance.
Subject(s)
Immunoglobulin Light Chains/genetics , RNA Editing/immunology , Receptors, Antigen, B-Cell/genetics , Animals , Autoantigens/immunology , Autoantigens/metabolism , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , Bone Marrow Cells/immunology , Cells, Cultured , Clonal Anergy/genetics , Gene Rearrangement, B-Lymphocyte, Light Chain/immunology , Immunoglobulin Light Chains/metabolism , Immunoglobulin Variable Region/genetics , Immunoglobulin Variable Region/metabolism , Immunoglobulin kappa-Chains/genetics , Immunoglobulin kappa-Chains/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Muramidase/immunology , Muramidase/metabolism , Receptors, Antigen, B-Cell/immunology , Receptors, Antigen, B-Cell/metabolism , Spleen/cytology , Spleen/immunologyABSTRACT
Clonal anergy of autoreactive B cells is a key mechanism regulating tolerance. Here, we show that anergic B cells express significant surface levels of CD5, a molecule normally found on T cells and a subset of B-1 cells. Breeding of the hen egg lysozyme (HEL) transgenic model for B cell anergy onto the CD5 null background resulted in a spontaneous loss of B cell tolerance in vivo. Evidence for this included elevated levels of anti-HEL immunoglobulin M (IgM) antibodies in the serum of CD5(-/-) mice transgenic for both an HEL-specific B cell receptor (BCR) and soluble lysozyme. "Anergic" B cells lacking CD5 also showed enhanced proliferative responses in vitro and elevated intracellular Ca(2+) levels at rest and after IgM cross-linking. These data support the hypothesis that CD5 negatively regulates Ig receptor signaling in anergic B cells and functions to inhibit autoimmune B cell responses.
