COL6A1 and arthritic joint disease: To address whether mesenchymal-specific p55TNFR signalling is also required for the development of arthritis, we crossed p55TNFR conditional knockout (KO) mice29 with Col6a1-Cre mice6 in order to generate animals which lack mesenchymal p55TNFR in their SFs (p55TNFRMs-KO) (Supplementary Figure 1A).