FOLLICULAR DENDRITIC CELL (FDC) PRECURSORS IN PRIMARY LYMPHOID-TISSUES

The origin of follicular dendritic cells (FDC) is unresolved cd, and a s such, remains controversial, Based on the migration of Ag-transporti ng cells (ATC) into lymphoid follicles and the phenotypic similarity b etween FDC and ATC, one hypothesis is that ATC may represent emigratin g FDC precursors, This contrasts with the view that FDC originate from local stromal cells in the secondary lymphoid tissues, Mice homozygou s for the severe combined immunodeficiency (prkdc(scid)) mutation (sci d) lack FDC, Thus, they provide a powerful tool for assessing de novo generation of FDC, To test whether FDC precursors could be found in bo ne marrow or fetal liver scid/scid mice were reconstituted with either : 1) bone marrow cells from (BALB/c x C57BL/6 F-1 donors, 2) bone marr ow cells from ROSA BL/6 F-1 (lacZ-transfected) mice, 3) rat hone marro w cells, or 4) rat fetal liver cells, Sis to eight weeks after reconst itution with F-1 bone marrow cells reactive with the FDC-labeling mAb, FDC-M1, also expressed donor class I molecules on their surfaces, Sim ilarly in mice reconstituted with lacZ-transfected bone marrow cells, these cells were also positive for the lacZ gene product, Furthermore, in spleens of animals reconstituted with either rat bone marrow or ra t fetal liver, rat FDC were identified using the specifically labeling mAb. ED5, In all cases host FDC were also present, indicating that sc id/scid mice have FDC precursors that will mature in the presence of a llogeneic or xenogeneic lymphoid cells, In summary, FDC can be derived from progenitor cells present in primary lymphoid tissues.