Targeted delivery of antigens to follicular dendritic cells via a monoclonal antibody specific for complement receptor 2 on marginal zone B cells: Dynamics of delivery and applications towards vaccine development

Antigens that have reacted with antibodies to form immune complexes (IC) and then fix complement are more immunogenic than free antigens and multiple lines of evidence suggest that complement opsonization plays a role in this enhanced immunogenicity. Opsonization of IC by complement, and their subsequent capture of C3b followed by its breakdown to C3dg allows these complexes to bind to the C3dg specific receptor, complement receptor 2 (CR2, CD21), on B cells. There is good evidence that C3dg-opsonized IC bound to marginal zone B cells are transferred to follicular dendritic cells (FDC) in the spleen and lymph nodes. I believe that a key step in the immune response to IC is the transfer of marginal zone B cell-bound IC to FDC. The mechanism of this in vivo reaction, "The B cell Transfer Reaction", has not yet been elucidated, and is the focus of my studies.;In order to target antigens for B cell-mediated delivery to the FDC I used model IC based on mAb 7G6. 7G6 is an anti-CR2 mAb that competes with C3dg for binding to CR2. My experiments in chapter 2 indicate that model IC constructed with mAb 7G6 can be transferred to the FDC. The most basic model IC consisted solely of the mAb 7G6. More complex model IC contained antigens directly bound to mAb 7G6. The hapten Alexa 488 or the protein antigen anthrax protective antigen (APA) was used for the immunization studies in chapter 3. Another IC that was used, which we have called a bispecific construct, consists of mAb 7G6 chemically cross-linked to an anti-antigen mAb. Bispecific constructs were used in experiments to determine if both mAbs remain cross-linked and colocalize to the FDC. These experiments were also performed with bispecific constructs containing various mouse monoclonal antibodies to determine if an anti-idiotype immune response could be produced in mice (chapter 4).