As TNF-RI has been shown to be crucial for RA-like polysynovitis in other TNF overexpression models (Diarra et al., 2007; Kontoyiannis et al., 1999), we tested whether TNF-RII may be more important than TNF-RI in the SpA-like phenotype of tmTNF tg mice. This evidence concerns the gene TNFRSF1B and rheumatoid arthritis.