Cellular Origin of Follicular Dendritic Cells

Abstract

Follicular dendritic cells (FDC) are found in follicles of all secondary lymphoid organs. These FDC bind and retain immune complexes on the surface of their dendrites and serve as a long term repository for unprocessed antigen which is believed to maintain both B cell memory and secondary antibody responses.¹ The origin of this unique cell type has not been unequivocally established. Several authors have studied the ontogenic development of FDC in lymphoid organs of rat,^2,3,4 mouse⁵ and rabbit.⁶ Based on a number of morphological similarities these investigators suggest that FDC are a differentiated form of fibroblastic reticulum cells. On the basis of enzyme histochemical studies on human FDC, Rademakers et. al.⁷ suggest FDC to be a differentiated form of mesenchymal cells. Based on studies with mouse radiation chimeras, Humphrey et al.⁸ concluded that follicular dendritic cell (FDC) precursors are not derived from the bone marrow. In this study, chimeras maintained for over a year continued to express H-2 antigens of host phenotype on the FDC. We have confirmed Humphrey’s observation (Kosco and Burton et. al., unpublished observations). However, in our studies an essential control failed. FDC are radioresistant and were not eliminated by doses of irradiation that exceeded 1200 R. Clearly the lymphocytes and macrophages were eliminated by high doses of irradiation but functional FDC were still present in the lymph nodes (Burton et al, unpublished). Thus it may be argued that on account of the radioresistant nature of FDC, host FDC were not eliminated from the recipients and their presence may have inhibited donor FDC from developing normally.