Follicular dendritic cell

A follicular dendritic cell (FDC) is a stromal cell type found in the light zone of the germinal center that captures and displays intact antigen on its surface for extended periods. Unlike classical dendritic cells, FDCs do not process antigen into peptides for MHC presentation; they preserve the native three-dimensional structure of antigens as immune complexes bound to complement receptors. This makes them the physical substrate of selection in affinity maturation: B cells must compete to pull antigen from FDC surfaces, and those with higher-affinity receptors win more antigen and thus more survival signals.

The FDC is not merely a passive display rack. It actively shapes the selection landscape by controlling antigen density, localization, and accessibility. In this sense, the FDC functions as a distributed evaluator in the germinal center's optimization algorithm — the objective function made cellular. Without FDCs, affinity maturation does not occur; the germinal center collapses into disorganized proliferation without direction.