FOLLICULAR DENDRITIC CELLS AND B-CELL CHEMOTAXIS

B cells isolated from germinal centers (GC) of immune mice 2-5 days af ter 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 wi th FDC either with or without anti-mu-dextran (anti-mu-dex) as an Ag s urrogate and/or recombinant interleukin (rIL)-4 as a T cell surrogate. After 3 days, the B cells were isolated and their migration to chemot actic factors contained in zymosan-activated serum assessed in microch emotaxis chambers. B cells incubated alone or with anti-mu-dex or rIL- 4 showed minimal migration, which could be increased if both anti-mu-d ex and rIL-4 were present. However, maximal migration was obtained whe n B cells were cultured with FDC, and this was not increased by additi on of anti-mu-dex and/or rIL-4, indicating that the FDC signal was a p rimary signal and did not require pre-activation of the B cells. Check erboard 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 cultur e, peaked by 48 h and decreased thereafter. Removal of FDC or interfer ence with FDC-B cell contact ablated or significantly decreased induct ion of B cell migration. Furthermore, induction did not require functi onal T cells. These data indicate that FDC can induce resting B cells to become responsive to chemotactic signals.