title: Evolving abundance and clonal pattern of human germinal center B cells during childhood.
abstract: Childhood is a critical period for the development of the memory B-lymphocyte repertoire necessary in protective humoral immunity. This study addressed the natural history of memory B cells based on the previous identification of germinal center and mantle zone cells as the probable precursor and mature memory cell populations, respectively. Using flow cytometric quantitation of these B-cell subpopulations in human tonsil, we found that germinal center cells were abundant (70% of tonsil B cells) during early childhood (2 to 3 years), but decline by early adolescence (8 to 14 years) to a low level (33%, P = .0003). To study the clonal evolution of these B-cell subpopulations, germinal center and mantle zone B cells were isolated using a preparative magnetic immunobead method, and analyzed using a novel polymerase chain reaction-based quantitative assay to measure the abundance of B-cell clones bearing certain rearranged VH subfamilies. Two VH subfamilies were informative: VH1N clones were uniquely deficient in germinal center B cells at the early age period, but became abundant in later childhood; and VH3L clones were absent among germinal center cells regardless of age. In contrast, B-cell clones bearing each VH subfamily were abundant in the mantle zone subpopulation throughout childhood. These findings suggest that the abundance and clonal pattern of germinal center B cells evolves during childhood, presumably due to changing antigenic or ontogenic processes. Moreover, the distinct clonal pattern of germinal center versus mantle zone B cells suggests that a major phase of clonal selection occurs after germinal center emigration.
authors.affiliation: Department of Pathology, UCLA School of Medicine 90024-1732.
authors.forename: Y
authors.initials: Y
authors.lastname: Valles-Ayoub
authors.forename: H L
authors.initials: HL
authors.lastname: Govan
authors.forename: J
authors.initials: J
authors.lastname: Braun
mesh_terms: D000293:Adolescent; D001402:B-Lymphocytes / Q000166:cytology*; D002454:Cell Differentiation; D002469:Cell Separation; D002648:Child; D002675:Child, Preschool; D002999:Clone Cells / Q000166:cytology; D005434:Flow Cytometry; D006801:Humans; D014066:Palatine Tonsil / Q000166:cytology*; D010641:Phenotype; D016133:Polymerase Chain Reaction