Figure 2. BALB/c mice develop an additional paLN in close vicinity to the knee joint.

(a) Section of paraffin-embedded hind leg from BALB/c mouse in the early chronic phase of RA with hematoxylin eosin staining. Arrows: periarticular lymph node (paLN) close to the knee joint and popliteal lymph node (pLN) embedded in fat tissue. Black bars, 400 μm. (b) paLN and popliteal lymph node stained for B cells (B220, blue) and T cells (CD3, red). (c) HE staining of cryosections of paLN in healthy untreated BALB/c mice (top) and 10 days after induction of arthritis (bottom). Black bars, 200 μm. (d) paLNs are connected to the vasculature. Biotinylated splenocytes were injected intravenously into arthritic mice. Eighteen hours after transfer, biotinylated cells (in red) could be detected in the spleen (top) and the paLN (bottom). Magnification X40. (e) paLNs are fully functional and develop GCs following arthritis induction. Characterization of the microarchitecture of the paLN from healthy and arthritic BALB/c mice: T cells were stained with peroxidase-labelled anti-CD3 antibody (in red) and several other lymph node and activation markers (in blue). FDC-M2 is a marker for FDCs, Lyve for lymphatic vessels, PNAd for high endothelial venules, PNA for GCs and Ki67 for proliferating cells. Only after arthritis induction, GCs are formed that harbour proliferating cells. The tissue sections represent two independent experiments with four animals per time point. Magnification: X40 for lymph nodes isolated 10 days after induction of arthritis and X100 for lymph nodes from healthy untreated mice. Black bars, 200 μm.