title: Ontogeny of B cells and pathogenesis of humoral immunodeficiencies.
abstract: Studies of B-cell ontogeny have played an important role in furthering our understanding of the pathogenesis of immunodeficiencies. Development of clonal diversity for both T and B cells begins during the first trimester and is far advanced by midgestation. Fetal and neonatal B cells have a limited capacity to express IgG and IgA antibody responses, although precursors expressing these immunoglobulin classes are present. T-and B-cell interactions in the neonate are dominated by suppression. T helper cells are present and functional, but their capacity to drive IgG and IgA responses is impaired. This paper will review the major steps in ontogenetic development of B cells and the functions associated with each differentiation stage. Possible pathogenetic mechanisms of several humoral immunodeficiency diseases are reviewed from the perspective of the normal progression of B-cell differentiation.
mesh_terms: D000818:Animals; D000916:Antibody Diversity; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation; D002999:Clone Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D006412:Hematopoietic Stem Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007126:Immunoglobulin Allotypes / Q000096:biosynthesis; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007136:Immunoglobulins / Q000096:biosynthesis*; D007153:Immunologic Deficiency Syndromes / Q000209:etiology* / Q000276:immunology / Q000473:pathology; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis
chemical_list: D007126:Immunoglobulin Allotypes; D007135:Immunoglobulin Variable Region; D007136:Immunoglobulins; D011947:Receptors, Antigen, B-Cell