Postmitotic LN MRC network is remodeled upon initial B cell colonization. (A) RAG-2°^/° Ubow mice were irradiated and reconstituted with RAG-2°^/° nonfluorescent BM cells to generate chimeric mice with dTomato-expressing stromal cells. Reconstituted chimeras were adoptively transferred or not with 6 × 10⁷ CMFDA-labeled polyclonal WT B cells to trigger FDC development in recipient LNs. 1 d later, peripheral LNs were sectioned, stained for RANK-L expression, and analyzed by confocal microscopy. L displays the width of the MRC network based on RANK-L staining. (B) The number of RANK-L⁺ dTomato⁺ cellular bodies was manually counted on tissue sections and used to calculate the density of the dTomato⁺ RANK-L⁺ MRC network in the two types of LNs, either in its globality (left) or in the first 30 µm below the SCS (right). Data are representative of 3 different experiments (2 mice per experiment, 6 LNs analyzed per mouse). (C) Representative high-magnification views of the MRC network present in the 2 types of LNs. (D) Auricular/cervical LN sections from Wnt-1Cre Ubow^+/+ RAG-2°^/° mice were stained for RANK-L expression and analyzed by confocal microscopy. Note the presence of MRCs Foci (F) in the SCS of these LNs devoid of B cells. Insets on the right display high-magnification views of MRC clusters. (E) Quantification of CFP⁺⁺ RANK-L⁺ MRC clustering index in the auricular/cervical LNs of Wnt-1Cre Ubow^+/+ RAG-2°^/° mice. A two-tailed Student’s t test was used to determine significance. *, P < 0.05; ***, P < 0.001. Bar = median. Data are representative of 5 individual mice (4 LNs analyzed per mouse) obtained in 2 independent experiments. Each dot represents one follicle. Bars, 25 µm.