To assess whether systemic administration of recombinant interferon‐γ (rIFNγ), a proinflammatory cytokine that influences the differentiation of naive T cells into Th1 cells, promotes the induction of arthritis in DBA/1 mice immunized with type II collagen (CII) in Freund's incomplete adjuvant (IFA) and to determine the antiarthritic effect of treatment with CII in IFA.

DBA/1 mice were immunized with CII in IFA and injected intraperitoneally with rIFNγ (8,000 units/mouse/day) or with recombinant interleukin‐12 (rIL‐12; 100 ng/mouse/day). In another experiment, mice were immunized with CII in Freund's complete adjuvant (CFA) and treated with a single dose of CII in IFA on the day of immunization or on the day of disease onset. Mice were monitored to assess the effect of the treatment on the severity of disease. Th1/Th2 cytokines and anti‐CII antibodies were measured by enzyme‐linked immunosorbent assay.

The administration of rIL‐12 or rIFNγ to mice immunized with CII in IFA restored the Th1 response and resulted in the development of arthritis. We then determined whether immunization with CII in IFA had the capacity to prevent and/or ameliorate collagen‐induced arthritis. A single intraperitoneal injection of CII in IFA prevented arthritis when given at the time of immunization with CII in CFA and reduced disease severity when given at the time of arthritis onset. The administration of CII in IFA resulted in a profound down‐regulation of IFNγ production and an up‐regulation of IL‐10 in cultures of draining lymph node cells.

These findings demonstrate that it is possible to deflect an ongoing pathogenic Th1 response to an antigen by reimmunization of the same antigen with a Th2‐polarizing adjuvant.