TNF and Arthritis: As an example the spontaneous development of arthritis in transgenic mice expressing mutant membrane TNF was directly attributed to the deregulation of membrane TNF production.23 Two novel mutants have been generated where the endogenous TNF was either replaced by a Δ1-9,K11E TNF allele24 or Δ1-12 allele,25 which represent a major advance allowing interesting insights in the role of membrane TNF in lymphoid structure development and inflammation.