NCF1 and Arthritis: The development of spontaneous arthritis in both rats and mice has been described as a result of genetic polymorphisms or mutations, for example in the genes Ncf1 (neutrophil cytosolic factor 1) (Hultqvist et al., 2004) and ZAP-70 [zeta-chain (TCR) associated protein kinase 70] (Sakaguchi et al., 2003), and as a result of environmental factors, such as the presence of commensal microbes (Wu et al., 2010) and hormonal and behavioural influences (Holmdahl et al., 1992b).