TNFRSF1A and Arthritis: To determine whether TNFR1 was needed in the hematopoietic compartment for the development of iBALT and NLH, we transplanted the bone marrow of BPSM1m/mTNFR1−/− donors into irradiated WT recipients and examined the mice 2 months later (again, time‐limited because of the development of severe arthritis).