Changes of immunoregulatory properties and induction of autoimmune reactivity to cartilage in rabbits with antigen-induced arthritis

Expression of cell adhesion molecules and cytokines in murine antigen-induced arthritis

Adhesion molecules and cytokines are important in chronic inflammatory conditions such as rheumatoid arthritis (RA) by virtue of their role in cell activation and emigration. Using immunohistochemical techniques we studied the expression of adhesion molecules and cytokines in cryopreserved sections of murine knee joint in the course of antigen-induced arthritis, an animal model of human RA. Various adhesion molecules and cytokines are expressed in the arthritic joint tissue. LFA-1, Mac-1, CD44, ICAM-1 and P-selectin were strongly expressed in the acute phase and to a lesser degree in the chronic phase of arthritis. VLA-4 and VCAM-1 appeared to be moderately expressed on day 1, L-selectin between days 1 and 3. LFA-1, Mac-1, CD44, alpha 4-integrin, ICAM-1 and the selectins were found expressed on cells of the synovial infiltrate, LFA-1, Mac-1 and ICAM-1 on the synovial lining layer, and VCAM-1 and P-selectin on endothelial cells. Expression of E-selectin could be demonstrated throughout the experiment at a low level in cells of the acute cell infiltrate. Cytokines, especially IL-2, IL-4, IL-6, TNF, and IFN-gamma, were heavily expressed during the acute phase of arthritis in cellular infiltrate. Taken together these data demonstrate that cytokines and their activation of adhesion molecules contribute to cell infiltration and activation during the initial phase of arthritis and to the induction and progression of tissue destruction in arthritic joints. These molecules might be potential targets for novel therapeutic strategies in inflammatory and arthritic disorders.

Different immunological mechanisms contribute to cartilage destruction in antigen-induced arthritis

Antigen-induced arthritis in guinea pigs was used as a model to investigate the pathogenic mechanisms responsible for cartilage destruction in chronic joint inflammation. The activation of macrophages, their effects on cartilage metabolism, and the development of autoimmunity to cartilage constituents were studied during the progression of arthritis. The results show that in arthritic animals the macrophages are systemically activated, with a peak in the early phase of inflammation. Interleukin 1, produced by the activated cells, suppresses the proteoglycan synthesis in cartilage explants and cultured chondrocytes and increases the proliferation of the cells in vitro. During the progression of arthritis humoral and cell-mediated immune responses to collagen type II and cartilage proteoglycans occur correlating with the severity of arthritis. It is concluded that different immunological mechanisms may be involved in cartilage destruction during antigen-induced arthritis. Mediator-induced metabolic reactions dominate in the early phase, whereas autoimmunity to cartilage might play an essential role in later phases of arthritis.

Humoral and cell-mediated sensitivity to cartilage constituents in mice with antigen-induced arthritis

Serum antibodies against native collagen type II and cartilage proteoglycans as well as proliferative responses of spleen lymphocytes to these antigens were evidenced during the progression of antigen-induced arthritis in mice. Because there were some correlations to the severity of arthritis, it is suggested that autoimmunity to cartilage constituents play a role for the persistence of the joint inflammation and cartilage destruction in this experimental model of chronic arthritis.

Effects of the immunomodulator diacetyl-splenopentin on antigen-induced arthritis in rabbits

Long-term treatment with the immunomodulator diacetyl-splenopentin reduces the severity of chronic joint inflammation and cartilage destruction in rabbits with antigen-induced arthritis. The level of specific antibodies as well as specific and non-specific cell-mediated immune reactivities including the proliferative response of spleen lymphocytes to cartilage proteoglycans in treated animals are lower than in untreated arthritic rabbits. Moreover, suppressor cell activity, which normally decreases during the early phase of inflammation, is enhanced and hyperreactive helper cell potential is reduced. These findings suggest that treatment with diacetyl-splenopentin normalizes the immune regulation, which is disturbed in the early phase of inflammation. This might result in a depression of the hyperreactive immune system including the autoimmunity developed against cartilage. Lowered immune reactivity in the joint in turn reduces the severity of chronic joint inflammation.