The follicles of secondary lymphoid tissues and germinal centres

These B-cell-rich areas are permeated by a dense network of follicular dendritic cells (FDCs). In follicles where no antigen-dependent activation is taking place, small recirculating B cells fill the spaces in the FDC network. In the first 3 weeks of T-dependent antibody responses, there is massive clonal expansion of B cells in follicles. This is associated with germinal centre formation. In the later stages of responses to protein antigens, small numbers of memory B blasts continue to proliferate in follicles for months or even a few years.

FDCs have the capacity to take up antigen in the form of antigen-antibody complexes and retain it for periods of many months. FDCs hold the antigen on their surface in a non-degraded form. In this respect they are completely different from Langerhans cells, IDCs and B cells, which process and present protein-based antigens to T cells. It seems likely that the antigen retained by these cells provides the drive for maintaining B-cell activation and indirectly T-cell activation during the months of the established phase of T-cell-dependent antibody responses.

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