IgM localizes within the conduit system of reactive LNs. (A) Confocal imaging of reactive and steady state auricular LNs from WT (C57BL/6J) or B cell–deficient (JHT) mice, 10 d after intradermal CFA immunization in the ears. Sections were stained for CD3, B220, collagen IV (col.IV), and IgM. Insets display high-magnification views of collagen IV+ conduits in the T cell zone. Bars, 100 µm (left panels); 10 µm (right panels). Data are representative of three experiments (two mice per condition and experiment). (B) Confocal imaging of auricular dLNs and contralateral ndLNs from Ccl19-Cre:RosatdT mice, 10 d after intradermal CFA injection in one ear. Sections were stained for collagen IV and IgM. tdT, tdTomato. Bars, 5 µm. Pictures are representative of three experiments (two mice per experiment). (C) Representative EM pictures of FRCs and conduits in steady state and auricular reactive LNs of WT and JHT mice, 10 d after intradermal CFA injection in one ear. Ultrathin sections were stained with 6-nm gold nanobeads specific for mouse IgM (highlighted with arrowheads), and the average number of beads located in the conduit lumen was evaluated for each condition. Bars, 2 µm (upper panels); 200 nm (lower panels). Data are representative of two experiments (one individual per condition and experiment). Results are expressed as mean ± SEM. *, P < 0.05; ****, P < 0.0001.
