CIA was induced in DBA-1 mice by injection of bovine collagen type II (CII) in complete Freund's adjuvant followed by a booster injection in incomplete Freund's adjuvant at day 21. At the first appearance of swollen joints, the mice were injected subcutaneously (s.c.) with BiP, a control protein, BSA or vehicle control (PBS). Disease progression was followed by measurement of swollen joints. At termination, splenocytes and draining lymph node cells were removed and T-cell cytokine secretion was assessed. Mixed spleens and lymph nodes from groups of DBA-1 mice that had been immunized s.c. with BiP or BSA (200 μg), or i.v. with BiP or BSA (10 μg), were collected 12 days after immunization. Cell cultures (2.5 × 106 cells/ml) were set up with 20 μg of the respective protein (BiP or BSA) for 5 days. Cells were then washed and injected intraperitoneally into DBA/1 mice (20 × 106 cells/mouse) that had received the first CII immunization 24 days previously. DR1+/+ IL-4 knockout mice, (n = 20) developed by backcrossing C57Bl/6 IL4-/- mice to DR1+/+ mice, were immunized with CII, and on day 24 after immunization were given 10 μg BiP i.v. Wild-type HLA-DR1+/+ transgenic mice (n = 20/group) were administered 10 μg BiP or PBS i.v.