Background/Purpose: Tumour necrosis factor (TNF) induced signaling events are important in lymphoid organ development and function, both in health and in immune-mediated inflammatory diseases such as arthritis. Important receptors involved in this process include TNF receptors (R) I and II that exert distinct functions. Mice overexpressing transmembrane ™TNF develop various features of chronic inflammation, including arthritis, that are mediated via TNFRI and/or TNFRII. In this study we investigated the contribution of TNFRI and TNFRII in spleen and peripheral lymph node (PLN) morphology in transgenic mice overexpressing tmTNF (tmTNF-tg).

Methods: Spleen and PLN were collected from wild type (wt) and heterozygous tmTNF-tg mice, with were either on a normal or TNFRI or TNFRII deficient background. Spleens were stained by immunofluorescence for B and T cell markers, imaged by confocal microscopy and analyzed using FIJI software. PLN were used for whole mount tissue staining for B and T cell markers, cleared, 3D imaged by light sheet microscopy and analyzed using Imaris software.

Results: TmTNF-tg mice exhibited an altered spleen morphology characterized by smaller follicles (tmTNF-tg 69.73 ± 72.25 µm²; wt 139.3 ± 71.36 µm²), and a reduced proportion of follicle T cell area (tmTNF-tg 15.22 ± 9.69%; wt 26.60 ± 10.46%). Spleen morphology of TNFRI^-/- and TNFRII^-/- mice was similar to wt mice. TmTNF-tg x TNFRI^-/- exhibited a normal spleen architecture (follicle size: 239.2 ± 250.5 µm²; T cell area: 29.92 ± 11.46%). In contrast, spleen follicles of tmTNF-tg x TNFRII^-/- mice had T cell areas (17.31 ± 8.88%) comparable to tmTNF-tg mice. PLNs of tmTNF-tg mice were increased in size (tmTNF-tg 3.74 ± 1.31 mm³; wt 2.41 ± 0.60 mm³), also in combination with deficiency of TNFRI (3.98 ± 2.07 mm³) or TNFRII (4.01 ± 1.96 mm³). TmTNF-tg PLNs had an increase in absolute B cell volume (tmTNF-tg 0.86 ± 0.33 mm³; wt 0.51 ± 0.07 mm³), but no change in B cell area as proportion of total PLN volume. The increased B cell volume was critically dependent on TNFRII. Interestingly, TNFRI deficiency caused profound alterations B cell area morphology that appeared as one peripheral layer of B cells covering a central T cell area rather than properly developed follicles.

Conclusion: This study demonstrates that overexpression of tmTNF leads to an aberrant spleen architecture, characterized by smaller follicles and reduced central T cell areas, which is critically dependent on TNFRI. In addition, overexpression of tmTNF results in enlarged PLN and increased total B cell volume, which is dependent on TNFRII, whereas TNFRI is more important in the proper organization of B cell follicles. Overall, this study employing different state-of-the-art (3D) imaging techniques highlights the importance of tmTNF-TNFR-induced signaling events in secondary lymphoid organ morphology and function, and reveals distinct roles for TNFRI and II. Advancing our knowledge in this field might provide a better understanding of the pathophysiology of TNF-associated diseases such as arthritis, which may be important to develop new or improved treatment strategies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differential-roles-of-tnfri-and-tnfrii-in-the-morphology-of-secondary-lymphoid-organs/