Follicular Dendritic Cells (BLymphocyte Stimulating)

Abstract

Follicular dendritic cells (FDCs) are found in all secondary lymphoid tissues, where they function as a repository of antigens to maintain long‐term IgG and IgE responses. Antigens are trapped and retained on FDCs in the form of immune complexes; and while most immune complexes require large quantities to induce an immune response, FDC‐trapped antigens are remarkably immunogenic and only a few picogram can induce microgram concentrations of a specific antibody. In addition to providing antigens, FDCs provide a number of additional signals (e.g. BAFF, IL‐6) that further contribute to antibody production. In addition to their contributions to immunity in health, FDCs are involved in some pathological situations including HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome), sarcoma/lymphoma, prion‐mediated transmissible spongiform encephalopathies (e.g. Creutzfeldt–Jakob) and Castleman disease. A further understanding of FDCs and their functions in both health and disease may aid our ability to better regulate immunity and ameliorate some disease states. Key Concepts FDCs trap antigens as immune complexes that consist of antigen in the presence of either specific antibodies or complement proteins, or both. FDCs trap immune complexes using CD32 and/or CD21. FDC‐trapped antigens or iccosomes are highly immunogenic and minute amounts (picogram) can induce significant quantities (microgram) of a specific antibody. FDC‐trapped antigens remain on the surface of FDCs and are not internalised. These antigens are not degraded but maintain their native configuration and immunoreactivity for many months. In addition to trapping conventional antigens, FDCs also trap HIV (and potentially other viruses) and maintain the infectious nature for many months. FDC‐trapped HIV can transmit infection to adjacent target cells (e.g. CD4 + T lymphocytes). FDCs provide both antigen and other signals that are central to the induction and maintenance of specific antibody responses. FDCs can play roles in both health and disease (e.g. HIV/AIDS, prion diseases and follicular lymphomas).