FOLLICULAR DENDRITIC CELLS AND THE MAINTENANCE OF IGE RESPONSES

Antigen (Ag) is retained for long periods of time in secondary lymphoi d tissues in the form of immune complexes on follicular dendritic cell s (FDC). Ag retained on FDC is thought to play a role in maintaining a ntibody (Ab) responses in vivo. A model for study of Ab production ind uced by retained Ag in vitro, is the spontaneous Ab response. In this response, specific Ab production is induced spontaneously (no exogenou s Ag needed) in cultures derived from secondary lymphoid tissues conta ining persisting Ag. Specific IgG is spontaneously induced and we reas oned that FDC may also play a role in the maintenance of specific IgE responses. To test this hypothesis, we monitored spontaneous anti-oval bmin (OVA) IgE production in cultures of lymph node (LN) fragments fro m OVA-immunized mice. In addition, highly enriched preparations of OVA bearing FDC were added to OVA-specific memory cells in an attempt to stimulate OVA-specific IgE production. Months after secondary immuniza tion, anti-OVA IgE responses were spontaneously induced when fragments from draining LN were placed into culture. Furthermore, FDC bearing O VA from draining LN induced anti-OVA ISE production when incubated wit h spleen cells from OVA-immune mice whereas identical cultures with FD C bearing environmental Ag from non-draining LN of the OVA immune anim als did not. The anti-OVA IgE responses were elicited only in cultures containing OVA-immune memory cells indicating that specific memory ce lls were critical for these anti-OVA IgE responses. Removal of FDC fro m cultures with an FDC-specific mAb dramatically decreased anti-OVA Ig E production. These studies demonstrate that FDC can induce specific m emory T and B cells to produce IgE and help support the concept that F DC-associated antigen may be involved in the long-term maintenance of specific IgE responses.