The in vivo effects of tumour necrosis factor blockade on the early cell mediated immune events and syndrome expression in rat adjuvant arthritis

SUMMARY Anti‐TNF therapy is effective in rheumatoid arthritis (RA); however, its mechanisms of action are incompletely understood. T cell‐driven mechanisms are thought to play an important role in RA and the effects of TNF blockade on these mechanisms are unclear. Adjuvant arthritis (AA) is a T cell dependent model of inflammatory arthritis. The aims of this study were to investigate the effects of TNF blockade on in vivo T cell cytokine expression and to clarify the role of TNF in the inguinal lymph nodes (ILN) in early arthritis. AA was induced in male DA rats. Rats received either 3 mg/kg or 10 mg/kg PEG sTNF‐RI at days 0, 2 and 4 postinduction or 10 mg/kg anti‐TNF antibody on day of arthritis induction. Control rats received either saline or normal sheep serum. Paw volume was assessed every 3–4 days. Rats were sacrificed on days 0, 6, 13 and 21 postinduction. Ankles were removed for quantitative radiology and histology. Synovium and ILN were removed for cell culture and to determine mRNA expression of cytokines using semiquantitative RT‐PCR. TNF and IFN‐γ protein production was measured using a bioassay and an ELISA. TNF blockade did not suppress mRNA expression of T cell cytokines in the ILN of rats in the early phase of AA, suggesting ongoing T cell activity. TNF protein production by ILN cells in culture was reduced in PEG sTNF‐RI treated rats, although mRNA expression was increased in the ILN prior to culture. Early administration of PEG sTNF‐RI did not attenuate AA, in contrast to an anti‐TNF antibody, which suppressed disease. A shorter half‐life for the PEG sTNF‐RI compared with the anti‐TNF antibody or the development of anti‐PEG sTNF‐RI antibodies may account for these results.