Heterogeneous effects of IFN-gamma in adjuvant arthritis.

In an attempt to evaluate the role of IFN-gamma in autoimmune arthritis, we tested the effects of IFN-gamma and anti-IFN-gamma mAb (DB-1) in various phases of arthritis development in a rat model for rheumatoid arthritis; the adjuvant arthritis (AA) model, induced by immunization with CFA. In addition, the effects of IFN-gamma were tested in vitro on T cell clones derived from rats afflicted with AA. T cell clone A2b, which has been shown to be arthritogenic secreted low amounts of IFN-gamma and its Ag-specific proliferation was inhibited by IFN-gamma. In contrast, clone A2c, which can inhibit the development of AA, produced high amounts of IFN-gamma and its proliferation was increased by IFN-gamma. In vivo administration of IFN-gamma 24 h before CFA caused an enhancement of arthritis, whereas giving IFN-gamma 24 to 48 h after CFA suppressed the disease. Administration of IFN-gamma between day +4 to +12 or between day +12 to +24 increased the severity of the first phase of the disease, but had no effect later. Administration of DB-1 1 to 2 days before adjuvant or between day +4 to +8 substantially decreased the disease, whereas DB-1 given from day +12 to +24 significantly enhanced it. Taken together, these results illustrate the heterogeneity of IFN-gamma in autoimmune arthritis and suggest a rational explanation for the possibly conflicting reports regarding the role(s) and effects of IFN-gamma in autoimmune processes. The multistage nature of T cell-mediated autoimmune arthritis may be due to the predominance of distinct T cell populations at different stages of the disease. The differences in the biologic activities of these T cells may be due to their patterns of lymphokine production.