Clearance of rHCII from the mouse circulation. HCII^−/− mice were injected intravenously with rHCII^WT (●, —) or rHCII^R189H (○, ----) as in Figure 2. Blood samples were collected 5 minutes, 1 hour, and 2 hours after injection, and the plasma HCII antigen was determined in duplicate by ELISA. HCII antigen values were normalized to the 5-minute point (100%). The half-life was calculated from the slope of the line fit to log(HCII antigen) versus time and was approximately 0.9 hour for each protein.