Germinal Center B Cells Present Antigen Obtained in vivo to T Cells in vitro and Stimulate Mixed Lymphocyte Reactions

Abstract

Shortly after secondary immunization, germinal center (GC) B cells have been observed in ultrastructural studies to obtain antigen from follicular dendritic cells (FDCs) in the form of immune complexes (1). This antigen appears to be degraded by GC B cells and may be processed for presentation to T cells. The present study was undertaken to determine if GC B cells can process and present antigen obtained from FDCs in vivo to appropriate T cells in vitro. In addition, the stimulatory capacity of GC B cells on T cells was evaluated in primary mixed lymphocyte reactions (MLR). The findings presented here demonstrate that antigen obtained in vivo by GC B cells can be processed and presented to T cells. The ability of GC B cells to interact with T cells is indicated by the fact that they served as potent stimulators of allogeneic T cells. In contrast, the small high density (HD) B cells are weak to negative stimulators under the same conditions. In addition, the GC B cells were even able to stimulate detectable syngeneic MLRs. These data suggest that in vivo, GC B cells are capable of interacting with T cells, in turn inducing the T cell help needed for the germinal center reaction, generating B memory cells, and influencing the high titers of antibody associated with the secondary antibody response.