Kallikrein–kinin system (KKS) assays. Plasma KKS protein concentrations in the human leukocyte antigen B27 transgenic rats treated with control monoclonal antibody IgG (filled bars) or monoclonal antibody C11C1 (open bars) at day 16 of the experimental protocol. Values were compared with a pool of normal Fischer 344 rat plasma. Both high-molecular-mass kininogen (HK) and prekallikrein (PK) were significantly decreased in the IgG1-treated group and were closer to normal in the C11C1-treated group. Both experimental groups showed decreased factor XI (FXI) with no significant differences between them. There were no significant changes between any groups in factor XII (FXII). ***P < 0.005.