Studies in rats have demonstrated that nerve injury induces a migration of macrophages into the DRGs. Because TNFa plays a key role in maturation of macrophages we investigated whether the occurrence of ED1 positive cells changes in sections of DRGs

(L1-L5) during antigen-induced arthritis (AIA) of one knee joint of the rat with and without therapy (post-treatment) of the rats with etanercept or infliximab. For control application of NaCl was used. DRGs (L1-L5) from both sites were removed from normal rats and from rats at 0 and 3 (each n=5 rats) days after induction of AIA. The ganglia were fixed, embedded, cut into sections and incubated with an anti-ED1 antibody. Using a computer based analysing system we analysed changes in the grey value of a 5 mm2 area in each DRG sections. Only very few ED1 positive cells were found in ganglia from normal rats. But the presence of ED1 positive cells in the DRGs of both sides was increased significantly in the ganglia 3 days after induction of AIA. Both after therapy with etanercept and infliximab the presence of ED1 positive cells was significantly reduced. We conclude that inflammation of a knee joint induces an activation of macrophages not only at the site of inflammation but also in the ganglia. TNFa appears to be one of the essential factors for the migration of ED1 positive cells into the ganglia.