Repeated antigen challenge modulates expression of follicular dendritic cell (FDC) related molecule in draining lymph nodes

Follicular dendritic cells (FDC) play a pivotal role in the regulation of humoral immunity, yet the regulatory mechanism of FDC remains largely unknown. Repeated antigen stimulation of 20 injections of HRP reduces the exchange of extant for newly arrived antigen on FDCs. This phenomenon might be related to the feedback regulation of FDC under extensive antigen stimuli. In the present study, for better understanding of the phenomenon, we observed the localization of fluorescence-labeled HRP injected after HRP stimuli of up to 40 injections with HRP under a fluorescent microscope, and examined antigen exchange on FDCs. Further, we also investigated the expression of marker proteins on FDCs in popliteal lymph nodes after repeated injections of HRP into the rat footpad. The decreased accumulation of fluorescent material in the germinal center (GMC) of lymph nodes indicated suppressed antigen exchange on FDCs after 20 and 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, ED5 positivity peaked and the reaction area was largest after 20 antigen injections, but weakened after 40 injections. MRC OX-2 reactions in GMC were decreased in 4 of 6 animals given 40 injections, but were positive in other animals. Decreased antigen exchange on FDC and its altered phenotype may play a role in the regulation of FDC function after repeated antigen stimuli.