Morphological study on the function of antigen transporting cell (ATC) and follicular dendritic cell (FDC) in the lymph node

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Antigen transporting cell (ATC) and follicular dendrtic cell (FDC) in the murine lymph node were investigated by electron microscopy and immunohistochemistry.1. After the immunization with two different antigens, horseradish peroxidase (HRP) and keyhole limpet hemocyanin (KLH), only HRP repeated injection induced the accumulation of large number of KLH, but no HRP on the processes of FDC in the lymph nodes. Antigen transporting cells (ATCs) located beneath the endothelial cells in the subcapsular sinus possessed both KLH and HRP.2. After elimination of the macrophages by MDPCl2 injections, MOMA- 1 positive cells disappeared in the subcapsular sinus in the lymph node. FDC-M1 positive cells remained near the subcapsular sinus and in the follicular area. Five days after the antigen injection, ATCs were presented in the MDPCl2 injected mice without MOMA-1 positive cells. ATC is different from the MOMA-1 positive cells.3. We investigated the expression of marker proteins on FDCs in popliteal lymph nodes after repeated injections of HRP into the rat footpads. The decreased accumulation of antigens in the germinal center (GMC) of lymph nodes indicated suppressed antigen exchange on FDCs after 40 antigen stimulations. S-100 protein reactions remained unchanged throughout the study, suggesting that the FDC population was preserved in GMC. On the other hand, EDS and MRC OX-2 reactions in GMC were decreased in animals given 40 injections. Decreased antigen exchange on FDC and its altered phenotype may play a role in the regulation of FDC function after repeated antigen stimuli.These experiments suggested that after antigen repeated injection, FDC was not destroyed, but may down regulate in the function. The different reaction of ATC and FDC for the antigens suggests these cells may be different type of cells.