Follicular dendritic cells and B cell chemotaxis.

B cells isolated from germinal centers (GC) of immune mice 2-5 days after antigen (Ag) challenge migrate in response to chemotactic signals, whereas GC B cells isolated at other times and resting B cells do not. Since B cells are in direct contact with follicular dendritic cells (FDC) in GC we reasoned that FDC might play a role in enabling B cells to become chemotactically active. Resting B cells were co-cultured with FDC either with or without anti-mu-dextran (anti-mu-dex) as an Ag surrogate and/or recombinant interleukin (rIL)-4 as a T cell surrogate. After 3 days, the B cells were isolated and their migration to chemotactic factors contained in zymosan-activated serum assessed in microchemotaxis chambers. B cells incubated alone or with anti-mu-dex or rIL-4 showed minimal migration, which could be increased if both anti-mu-dex or rIL-4 were present. However, maximal migration was obtained when B cells were cultured with FDC, and this was not increased by addition of anti-mu-dex and/or rIL-4, indicating that the FDC signal was a primary signal and did not require pre-activation of the B cells. Checkerboard analysis using variation in concentration and location of the chemoattractant in chemotaxis chambers indicated that both chemotaxis and chemokinesis occurred. B cell migration began within 6 h of culture, peaked by 48 h and decreased thereafter. Removal of FDC or interference with FDC-B cell contact ablated or significantly decreased induction of B cell migration. Furthermore, induction did not require functional T cells. These data indicate that FDC can induce resting B cells to become responsive to chemotactic signals.