Cytokine regulation in rodents with experimental arthritis

The general aim of this project has been to try to elucidate the mechanisms behind induction of arthritis by using in situ hybridization and immunohistochemical methods to analyse the dynamics of the cytokine network in vivo, in the peripheral Iymphoid system and in the joints of rodents with collagen-induced arthritis (CIA)and oil-induced arthritis (OIA).

We first examined the kinetics of cytokine gene expression in vivo, in the draining Iymph nodes of DA rats following immunization with rat type II collagen (RCII) emulsified in Freund's incomplete adjuvant oil (FIA) or with only FIA, which are regimens that induce CIA and OIA, respectively. We also investigated if inhibition of arthritis through inclusion of an irrelevant antigen, ovalbumin (OVA) in the emulsions was associated with an altered cytokine production. A rapid and pronounced expression of TNFa mRNA was observed in RCII/FIA and FIA immunized rats but not in OVA/FIA immunized animals, which instead expressed IL-4 mRNA.

We further compared the cytokine secretion pattern in the draining lymp nodes of arthritis susceptible DA rats and non-susceptible F344 and DA MHC congenic PVG. IAV 1 rats following RCIVFIA immunization. In contrast to DA rats which did not express IL-4, immunization of RCII/FIA in F344 rats and PVG IAVI rats was characterized by induction of IL-4 mRNA. Moreover, TNFa, IL-2 and IFNr mRNA expression was significantly reduced compared to DA rats at all timepoints studied. We also investigated which cell population is involved in OIA by using adoptive transfer. The results indicate that polyclonal CD4+ cells expressing a type I cytokine secretion pattern could transfer OIA.

As induction of TNFa synthesis in CIA appears to be a key feature in the induction of the disease, the effect of Rolipram, a drug with documented downregulatory effect on TNFa, was evaluated in the CIA model. An ameliorative effect of Rolipram on the development of arthritis was recorded, an effect associated with a profound reduction in the expression of TNFa and IFNy.

The presence of TGFß isoforms and TGFß receptor-expressing cells was examined in the synovial tissue of arthritic rats during the course of CIA, and an abundant expression of TGFßs and its receptors in arthritic joints was demonstrated. Finally, we analysed the dynamics and distribution of cytokine production in arthritic limbs of mice with CIA. A dominant and universal presence of monokines in contrast to a paucity of T cell-derived cytokines throughout the disease process was recorded. Moreover, differences in cytokine patterns at various stages of disease were observed with T cell-derived cytokines (IFNy) only being expressed during the initial phase of disease and monokines being expressed during all phases of disease.

Our results indicate that (I) a strong local expression of TNFa may be important for the induction of arthritis, (2) the elicitation of an immune reaction against an irrelevant antigen, may inhibit arthritis development by contributing to a shift in the initial arthritogenic cytokine response, (3) non-MHC gene(s) determine the direction of the anti-RCII response towards a type I disease-promoting, or a type2 disease-limiting response, (4) a type I cytokine response may be important in the induction of experimental arthritis.