title: In vivo obtained antigen presented by germinal center B cells to T cells in vitro.
abstract: Shortly after secondary immunization germinal center (GC) B cells obtain antigen from follicular dendritic cells (FDC) in the form of immune complexes. This antigen appears to be degraded by the GC B cells and may be processed for presentation to T cells. The present study was undertaken to determine whether GC B cells can process and present antigen obtained from FDC in vivo to appropriate T cells in vitro. GC B cells were isolated from immune mice with the use of Percoll density separation followed by a panning procedure which utilizes the ability of the plant lectin, peanut agglutinin (PNA), to selectively bind to GC B cells. The enriched GC B cells were approximately 80% highly positive for PNA, 97% positive for Ia and surface IgM, but less than 0.01% positive for Thy-1.2 or esterase. In some experiments, this population was further purified to near 100% highly PNA-positive cells with the use of fluoresceinated PNA and a fluorescence-activated cell sorter. Cell sorting analysis indicated that the antigen (125I-labeled ovalbumin (OVA)) was restricted to the highly PNA-positive cell fraction. The capacity of these highly PNA-positive B cells to present antigen was assessed by monitoring interleukin 2 (IL-2) production by the OVA-specific T cell hybridoma, 3DO-54.8. GC B cells obtained from mice 3 wk or more after secondary immunization did not elicit IL-2 production in the absence of added OVA. However, GC B cells isolated as early as 1 day and for over 1 wk after a challenge with OVA, were able to stimulate high levels of IL-2 production, in the absence of adding OVA to the cell cultures. This response was maximal on day 5 and corresponded precisely with the kinetics of the ultrastructural studies which document the uptake of antigen by GC B cells in vivo. The FDC-derived antigen was remarkably immunogenic when compared with exogenous antigen. These findings demonstrated that antigen obtained in vivo by GC B cells could be processed and presented to T cells. In vivo, GC B cells may induce the T cell help needed for the germinal center reaction, generate B memory cells, and help induce the high titers of antibody associated with the secondary antibody response.
authors.affiliation: Department of Microbiology and Immunology, Medical College of Virginia, Richmond 23298.
authors.forename: M H
authors.initials: MH
authors.lastname: Kosco
authors.forename: A K
authors.initials: AK
authors.lastname: Szakal
authors.forename: J G
authors.initials: JG
authors.lastname: Tew
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D000941:Antigens / Q000032:analysis / Q000276:immunology*; D001402:B-Lymphocytes / Q000145:classification / Q000276:immunology*; D002469:Cell Separation; D005260:Female; D005434:Flow Cytometry; D007700:Kinetics; D037102:Lectins; D008198:Lymph Nodes / Q000166:cytology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D019887:Peanut Agglutinin; D010641:Phenotype; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000941:Antigens; D037102:Lectins; D019887:Peanut Agglutinin