An Antigen Depository of the Immune System: Follicular Dendritic Cells

Follicular dendritic cells (FOe) are unique among cells of the immune system. While their morphological characteristics re sulted in their inclusion as a 'dendritic cell type', tt1ey differ quite significantly from the other members of the dendritic cell family. In contrast to T-cell-associated dendritic cells or the Langerhans cells found in the skin, FOe reside in highly organized B cell follicles within secondary lymphoid tissues. This site of resi dence provided a nomenclature committee in 1982 with the second descriptive factor for the derivation of their name. The cardinal feature of FOe is to trap and retain antigen on the surface of their dendritic processes for extended amounts of time and it is this feature that provides the conceptual compo nent for the title of this book. In response to an antigenic challenge, primary B cell follicles undergo dynamic events, giving rise to germinal centers which are associated with activation, expansion, and differentiation processes of B cells. The interactions of B cells with Foe and T cells in the germinal centers are essential for generating the complete repertoire of antibody isotypes obtained during an antibody response. In addition, stimuli either initiated or main tained during the germinal center reponse leads to production of high affinity antibodies through the processes of somatic muta tion and clonal selection. In this context, FOe act as a pivotal source of antigen. They accumulate foreign proteins (e. g.