Progress in the Understanding of Inducible Models of Chronic Arthritis

Modulation of adjuvant arthritis in the rat by 2-methoxyestradiol: an effect independent of an anti-angiogenic action

Angiogenesis is a prominent feature in rheumatoid arthritis. 2-methoxyestradiol (2ME2) inhibits endothelial cell proliferation, and angiogenesis in vivo. We evaluated the effect of 2ME2 in rats with adjuvant arthritis (AA), an autoimmune T-cell-dependent polyarticular arthritis induced by immunization with Mycobacterium organisms. Rats were immunized with Mycobacterium butyricum and arthritis was assessed clinically, by radiolabeled blood neutrophil (PMNL) migration to joints and by histology. Treatment with 2ME2 (30 mg/kg/d or 100 mg/kg/d) from day 6 post-immunization inhibited arthritis severity on day 14 (vehicle clinical score=11.2; 2ME2 groups=7-8, p<0.05). When treatment was delayed until signs of clinical arthritis on day 10 post-immunization, 2ME2 treatment still inhibited arthritis severity. PMNL migration to the joints was significantly inhibited (by 35-40%; p<0.01) by early 2ME2 treatment (day 6-14). Treatment with 2ME2 inhibited PMNL migration to dermal inflammation induced by TNF-alpha but not by LPS or C5a. Joint histology revealed decrease in leukocyte infiltration and especially in cartilage damage. However, synovial vascularity was not affected by 2ME2 treatment. The marked splenomegaly, splenitis and lymphoid hyperplasia associated with AA were prevented by 2ME2 therapy. Furthermore, the ex vivo proliferative response to mycobacterial antigen (PPD) of lymphocytes from 2ME2-treated rats with AA was markedly diminished, although response to mitogens was unaffected. Thus 2ME2 has anti-arthritic properties with a disease-modifying action, separate from its anti-angiogenic properties. The selective inhibition of TNF-alpha-induced leukocyte recruitment, lymphoid hyperplasia and attenuated recall response to antigen suggests both immunomodulatory and anti-inflammatory actions of 2ME2.

The role of tumour necrosis factor-alpha and IL-1 in polymorphonuclear leucocyte and T lymphocyte recruitment to joint inflammation in adjuvant arthritis

The mediators involved in leucocyte recruitment to joints during arthritis are not fully defined, but two important proinflammatory cytokines, IL-1 and tumour necrosis factor-alpha (TNF-alpha), are produced in joints in rheumatoid arthritis (RA). We investigated in the rat adjuvant arthritis model whether endogenous IL-1 and TNF-alpha contribute to joint inflammation and polymorphonuclear leucocyte (PMNL) and T lymphocyte infiltration. The migration of 51Cr-labelled rat blood PMNL and 111In-labelled T lymphocytes to the joints of rats with adjuvant arthritis was measured along with plasma protein extravasation, which was quantified using 125I-labelled human albumin. Rats with active arthritis of 5 days' duration received i.p. non-immune serum, polyclonal neutralizing anti-serum to rat TNF-alpha, antiserum to IL-1 alpha and IL-1 beta, or both anti-TNF plus anti-IL-1 for 5 days. Treatment with anti-IL-1 alpha and IL-1 beta did not affect plasma protein extravasation, or PMNL or T lymphocyte accumulation in the joints (i.e. talar joint, hind paws, and tail) despite the fact that this treatment inhibited 80-90% of the PMNL migration into dermal sites injected with IL-1 alpha or IL-1 beta. In contrast, anti-TNF-alpha treatment significantly improved clinical scores, decreased plasma protein extravasation by 60-80%, inhibited PMNL accumulation by 40-50% and decreased T lymphocyte accumulation by 30-50%. Treatment with anti-IL-1, together with anti-TNF-alpha, significantly potentiated the inhibition of T lymphocyte accumulation observed with anti-TNF-alpha alone. These results indicate that endogenous TNF-alpha production may play an important role in the inflammatory changes and leucocyte recruitment in this experimental model of human arthritis, while IL-1 may have a less important role in leucocyte recruitment to these joints.

T lymphocyte migration to arthritic joints and dermal inflammation in the rat: differing migration patterns and the involvement of VLA-4

The migration of T lymphocytes into arthritic joints of rats with adjuvant arthritis was examined and compared to the accumulation of the same cells in cutaneous inflammation, since previous studies had shown that only a subpopulation of T lymphocytes, found enriched in peritoneal exudates (sPEL), migrated efficiently to cutaneous inflammatory sites. Surprisingly, lymphocyte migration to the inflamed joint included T cells from most of the recirculating lymphocyte pool, including sPEL, spleen, peripheral lymph node (PLN), and Peyer's patches, and was much more rapid than migration through either cutaneous sites or PLNs. Treatment of sPEL with antibody to VLA-4 inhibited sPEL accumulation in the joints, while anti-VLA-4 treatment did not affect the accumulation of PLN T cells. It is concluded that the arthritic joint not only attracts inflammation-seeking lymphocytes (sPEL), through at least a partially VLA-4 dependent interaction, but also large numbers of lymphocytes which normally migrate to PLNs through a VLA-4-independent mechanism.

Bisphosphonates in collagen arthritis

Bisphosphonates suppress bone destruction in various diseases. We studied the effects of 3-amino-hydroxypropylidene-1,1-bisphosphonate (APD), and dimethyl-APD in the collagen model of chronic arthritis in rats. The incidence and severity of arthritis was not lower in rats treated with APD or dimethyl-APD compared with controls. The cellular and humoral immune responses to collagen were also similar in the treated and untreated animals. In all animal groups the same bone destruction was found radiographically 42 days after immunization. This study demonstrates that bisphosphonates do not suppress the course of collagen arthritis in rats.

Collagen arthritis in rats, arthritogenic lymphokines and other aspects

This review will mainly highlight data from selected, independent studies which collectively implicate a primary role for T cells in the pathogenesis of collagen arthritis in rats. Conferring insusceptibility to this experimental disease with the use of polyclonal, T cell specific antiserum provided direct initial evidence for this conclusion. Substantiation for the theory of a dominant T cell role in collagen arthritis was afforded by T cell line vaccination; scrutiny showed that the mechanism accounting for this protection was a specific down-regulation of the cellular response to collagen. Additional support came from experiments which showed that as few as 10(3) type II collagen specific T line cells were capable of provoking a sustained proliferative synovitis when instilled into the knee joint cavity of syngeneic naive rats. Further analysis of this phenomenon revealed that the arthritogenic capacity of various collagen-reactive line cells correlated with their ability to release a 65-Kd, collagen-binding lymphokine. This antigen-specific lymphokine was designated arthritogenic factor, based on an arthritogenic activity in the knee joint bioassay similar to that of the cells. A functional and physicochemically identical rat arthritogenic factor has also been identified in the adjuvant model of arthritis. These data support the premise that a major effector mechanism in experimental rat arthritis is the release of arthritogenic factor by expanded clones of autoreactive T cells; they also indicate that substantive efforts should be undertaken to seek to identify arthritogenic factor-like lymphokines in patients with chronic inflammatory synovial disease. As an equally plausible alternative hypothesis, the review will close with a brief discussion of recent findings supporting the possible involvement of cartilage-binding, complement-fixing anti-type II collagen antibodies in the pathogenesis of rheumatoid arthritis.