title: Human memory B cells.
abstract: A key feature of the adaptive immune system is the generation of memory B and T cells and long-lived plasma cells, providing protective immunity against recurring infectious agents. Memory B cells are generated in germinal center (GC) reactions in the course of T cell-dependent immune responses and are distinguished from naive B cells by an increased lifespan, faster and stronger response to stimulation and expression of somatically mutated and affinity matured immunoglobulin (Ig) genes. Approximately 40% of human B cells in adults are memory B cells, and several subsets were identified. Besides IgG+and IgA+memory B cells, ∼50% of peripheral blood memory B cells express IgM with or without IgD. Further smaller subpopulations have additionally been described. These various subsets share typical memory B cell features, but likely also fulfill distinct functions. IgM memory B cells appear to have the propensity for refined adaptation upon restimulation in additional GC reactions, whereas reactivated IgG B cells rather differentiate directly into plasma cells. The human memory B-cell pool is characterized by (sometimes amazingly large) clonal expansions, often showing extensive intraclonal IgV gene diversity. Moreover, memory B-cell clones are frequently composed of members of various subsets, showing that from a single GC B-cell clone a variety of memory B cells with distinct functions is generated. Thus, the human memory B-cell compartment is highly diverse and flexible. Several B-cell malignancies display features suggesting a derivation from memory B cells. This includes a subset of chronic lymphocytic leukemia, hairy cell leukemia and marginal zone lymphomas. The exposure of memory B cells to oncogenic events during their generation in the GC, the longevity of these B cells and the ease to activate them may be key determinants for their malignant transformation.
authors: Institute of Cell Biology (Cancer Research), Medical Faculty, University of Duisburg-Essen, Essen, Germany.
authors: M
authors: M
authors: Seifert
authors: Institute of Cell Biology (Cancer Research), Medical Faculty, University of Duisburg-Essen, Essen, Germany.
authors: R
authors: R
authors: Küppers
mesh_terms: D001402:B-Lymphocytes / Q000145:classification / Q000166:cytology / Q000276:immunology*; D006801:Humans; D007132:Immunoglobulin Isotypes; D007156:Immunologic Memory; D009369:Neoplasms / Q000473:pathology
chemical_list: D007132:Immunoglobulin Isotypes