title: In vivo imaging of germinal centres reveals a dynamic open structure.
abstract: Germinal centres are specialized structures wherein B lymphocytes undergo clonal expansion, class switch recombination, antibody gene diversification and affinity maturation. Three to four antigen-specific B cells colonize a follicle to establish a germinal centre and become rapidly dividing germinal-centre centroblasts that give rise to dark zones. Centroblasts produce non-proliferating centrocytes that are thought to migrate to the light zone of the germinal centre, which is rich in antigen-trapping follicular dendritic cells and CD4+ T cells. It has been proposed that centrocytes are selected in the light zone on the basis of their ability to bind cognate antigen. However, there have been no studies of germinal-centre dynamics or the migratory behaviour of germinal-centre cells in vivo. Here we report the direct visualization of B cells in lymph node germinal centres by two-photon laser-scanning microscopy in mice. Nearly all antigen-specific B cells participating in a germinal-centre reaction were motile and physically restricted to the germinal centre but migrated bi-directionally between dark and light zones. Notably, follicular B cells were frequent visitors to the germinal-centre compartment, suggesting that all B cells scan antigen trapped in germinal centres. Consistent with this observation, we found that high-affinity antigen-specific B cells can be recruited to an ongoing germinal-centre reaction. We conclude that the open structure of germinal centres enhances competition and ensures that rare high-affinity B cells can participate in antibody responses.
authors.affiliation: Laboratory of Molecular Immunology, The Rockefeller University, New York, New York 10021, USA.
authors.forename: Tanja A
authors.initials: TA
authors.lastname: Schwickert
authors.forename: Randall L
authors.initials: RL
authors.lastname: Lindquist
authors.forename: Guy
authors.initials: G
authors.lastname: Shakhar
authors.forename: Geulah
authors.initials: G
authors.lastname: Livshits
authors.forename: Dimitris
authors.initials: D
authors.lastname: Skokos
authors.forename: Marie H
authors.initials: MH
authors.lastname: Kosco-Vilbois
authors.forename: Michael L
authors.initials: ML
authors.lastname: Dustin
authors.forename: Michel C
authors.initials: MC
authors.lastname: Nussenzweig
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology; D002448:Cell Adhesion; D002450:Cell Communication; D002465:Cell Movement; D018858:Germinal Center / Q000166:cytology* / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL