SUMMARYThe aim of this study was to understand the immune processes controlling the initiation and spontaneous resolution of adjuvant arthritis (AA). We investigated synovial T-cell recruitment and mRNA expression of IL-17 and other important disease related cytokines, IFN-g , IL-2, IL-4, TNF and TGF-b in inguinal lymph node (ILN) and synovial membrane (SM). Arthritis severity was assessed by a numerical rating score and rats were sacrificed every 3±4 days postadjuvant induction. Further assessment involved quantitative radiology and histology of the ankle joints on each day, and the ILN and SM were removed for RNA extraction. Cytokine mRNA expression was measured using RT-PCR and densitometry. Paraffin sections of rat ankle joints were stained for T-cells (CD3) by immunohistochemistry. In the ILN, there was an increase in IL-17, TNF and IFN-g expression in the early stages of disease, with a secondary sustained increase in IFN-g expression. In the SM, there was expression of T-cell cytokines in early arthritis (day 13), and prolonged TNF and TGF-b expression, which reflected disease progression. IL-4 mRNA expression increased in the later stages of AA. Synovial T-cell numbers transiently increased at day 6, and remained high from days 13±28. Increased pro-inflammatory cytokine expression, including IL-17, in the ILN reflects the initiating events in the early stage of disease. IL-17 may therefore play an important role in the pathogenesis of AA. The increase in IL-4 (an antiinflammatory cytokine) in the SM in the later stages of AA suggests that IL-4 is involved in the spontaneous resolution of AA. The initial increase in IFN-g in the ILN may reflect a pro-inflammatory response, while the prolonged secondary increase may indicate activation of regulatory T-cells.

SUMMARYIL-17 is a T cell cytokine with a complex and important role in the immune system. It has been detected in rheumatoid arthritis (RA) synovial membrane and found to stimulate the production of the proinflammatory cytokines IL-6, IL-8, tumour necrosis factor-alpha (TNF-a ) and granulocytemacrophage colony-stimulating factor (GM-CSF) in vitro. To date, there are few data available on the agents that stimulate IL-17 production. We therefore investigated the in vitro IL-17 response to a variety of mitogens and antigens, and compared the IL-17 response to interferon-gamma (IFN-g), IL-4, IL-10 and TNF-a . In this study we used a type-0 antigen, tetanus toxoid (TT), a type-1 antigen, PPD from Mycobacterium tuberculosis, a potential type-2 rye grass (RG) antigen (Lol I) and an autoantigen SS.B (La), to stimulate PBMC from healthy controls. Cytokine mRNA was measured using semiquantitative reverse transcriptase-polymerase chain reaction and cytokine protein measured using specific ELISA techniques, while the frequency of IL-17-producing T cells was determined by flow cytometry. The mitogens concanavalin A, phytohaemagglutinin and phorbol myristate acetate/ ionomycin induced a significant increase in IL-17, with the highest levels being produced by anti-CD3/anti-CD28 stimulation. The antigens TT and PPD significantly increased IL-17 mRNA expression over time, but failed to have such an effect at the protein level. IL-17 protein was also detectable in both antigen-specific (TT, SS.B) and non-specific T cell clones, but at levels lower than IFN-g . IL-17 production did not correlate with either the type-1 cytokine IFN-g or TNF-a or the type-2 cytokine IL-4 or IL-10 at either the mRNA or protein level.

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