Locally produced, Ag-specific IgM localizes within the conduit system of reactive LNs. (A) HEL-specific MD4 IgM_a⁺ B cells and OVA-specific OT-II CD4⁺ T cells were adoptively transferred into WT mice. The next day, recipient mice were injected intradermally with an HEL-OVA chimeric protein emulsified in CFA, in one ear. 4 d later, auricular dLNs and contralateral ndLNs were harvested. Sections were stained for collagen IV (Col.IV), B220, and IgM_a and imaged by confocal microscopy. tdT, tdTomato. Bars, 200 µm (left panels); 10 µm (right panels). Data are representative of three experiments (two mice per experiment). (B) Confocal imaging of reactive and contralateral LNs from Ccl19-Cre:Rosa^tdT recipient mice treated as described in A. Bars, 5 µm. Data are representative of two experiments (two mice per experiment).