Fig. 6.

Naive lymphocytes and LTβR signaling are required to trigger FRC expansion. Total LN cellularity, as well as the number and proliferation of FRCs, were measured by flow cytometry in six draining LNs at 5.5–6 d (A, B, D–F) or 3 d (C) after the indicated immunization. (A) WT or T/B-cell-deficient (RAG2 KO) mice were immunized s.c. with PBS or WT BMDCs activated with CpG without OVA antigen. (B) WT mice received i.p. injections of PBS or IL-7/α-IL-7 complexes each day for the first 4 d. (C and D) Mice that received OT T cells were injected with LTβR-Fc or control (ctrl) IgG and then immunized with OVA/Mont or PBS, followed by the flow cytometry analysis of six draining LNs at day 3 (C) or day 5.5 (D) after immunization. (E) Representative histogram (Left) and mean fluorescence intensity (MFI; Right) for the surface expression of LTβR on FRCs in LNs of PBS-injected (black line) or OVA/Mont-injected (dashed line) mice. Surface protein expression on CD45⁺ cells served as a negative control (gray area). (F) OT T cells were adoptively transferred into CD11c-DTR tg or ntg littermate mice, which were then immunized s.c. with OVA/Mont and received a single dose of DT at 3 d after immunization. Data are pooled from two independent experiments that are represented by circles and triangles. Data are mean ± SD, either representative of (A, C, and E) or compiled from (B, D, and F) at least two experiments, with n ≥3 mice per experiment.