Background/Purpose: Tumour necrosis factor a (TNF) is important in immune-mediated inflammatory diseases such as spondyloarthritis (SpA). Transmembrane ™TNF-transgenic (tg) mice that overexpress tmTNF develop typical SpA symptoms, including inflammation, bone destruction and bone formation. Interestingly, these mice also develop lymphoid aggregates in the bone marrow (BM) of the axial and peripheral skeleton. We characterized the lymphoid aggregates in the context of angiogenesis and inflammation.

Methods: Ankles, femora, tibiae, vertebrae and spleens from tmTNF tg mice and wild-type (WT) littermates (6 weeks, 12 weeks, and 8 months old; n=5 per age per group) were dissected and analyzed by confocal microscopy. In addition, 12 week old mice (n=6 per group) were analyzed by flow cytometry. To study the importance of TNF-R signaling in these processes, tmTNF tg mice lacking TNF-RI (tmTNF tgxTNF-RI^-/-) or TNF-RII (tmTNF tgxTNF-RII^-/-) (n=5 per group) were investigated.

Results: Immunofluorescent (IF) evaluation demonstrated that BM of tmTNF tg mice contained extensive lymphoid aggregates, both in the vertebrae and the ankles, but not in the femurs. The aggregates in the BM progressed with age and contained characteristics of ectopic lymphoid structures (ELS) consisting of B220⁺ B cells, CD3⁺ T cells, expression of the germinal center marker peanut agglutinin (PNA) and FDC-M1⁺ follicular dendritic cells that are in close proximity of MECA79⁺ high endothelial venules (HEVs). Quantification showed a median of 2 aggregates per vertebra in the tmTNF tg mouse, while there were none in the WT (P=0.001). Flow cytometric analysis revealed that tmTNF tg vertebrae contained a significantly higher amount of B cells (P=0.002) and more IgD^–CD95⁺ germinal center B cells per B cell (P=0.002) with a higher expression of the costimulatory molecules CD80 (P=0.002) and CD86 (P=0.002) compared to vertebrae of WT animals. The vertebrae also contained significantly more CXCR5⁺PD-1⁺FoxP3^–CTLA4^– T follicular helper cells (P=0.026), CXCR5⁺PD-1⁺FoxP3⁺CTLA4⁺ T follicular regulatory cells (P=0.02) and CXCR5^–PD-1^–FoxP3⁺ T regulatory cells (P=0.01) in tmTNF tg mice. Meanwhile, B cell development in the BM of tmTNF tg femurs and vertebrae was not altered. Furthermore, BM, spleen and vertebrae from tmTNF tg mice contained significantly more IgA⁺ plasma cells compared to WT littermates. Of note, tmTNF tgxTNF-RI^-/- mice did not display lymphoid aggregates or HEVs in the BM, while tmTNF tgxTNF-RII^-/- mice did, although to a lesser extent than tmTNF tg mice. Likewise, tmTNFa tgxTNF-RI^-/- mice did not develop macroscopic inflammation in spine and ankle joints, while the tmTNF tgxTNF-RII^-/- mice did.

Conclusion: tmTNF overexpression in mice induces ELS in BM and supports IgA⁺ plasma cell differentiation. These effects are critically dependent on TNF-RI signaling and may underlie SpA pathology, as BM edema and elevated serum IgA have also been described in SpA patients.

« Back to 2019 ACR/ARP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/inflammatory-processes-in-experimental-spondyloarthritis-are-accompanied-by-formation-of-ectopic-lymphoid-structures-and-b-cell-lineage-alterations-in-the-bone-marrow/