Effect of an anti-C5 miniantibody on thrombus formation and vessel occlusion induced by aPL-positive IgG in LPS-treated rats. The animals received 1 mg of either the anti-C5 miniantibody (□) or an unrelated miniantibody (▪) intravenously 15 minutes before the infusion of aPL-positive IgG (10 mg/1 mL sterile saline). The IgG from 3 patients with APS (A, C, and D) and from 3 healthy control subjects were used. In parallel experiments the miniantibody used at this concentration was found to completely neutralize the serum C activity for 20 minutes and to maintain this activity to 50% of the starting value up to 5 hours after infusion (data not shown). Thrombi (A) and vessel occlusions (B) were significantly reduced in the rats treated with the miniantibody to C5. These parameters were evaluated on 2 rats from each IgG sample. The results are expressed as mean ± SD. ^*P < .05 versus control rats receiving the unrelated miniantibody. Immunofluorescence analysis of the mesenteric tissue from LPS-treated rats that received aPL-positive IgG and anti-C5 miniantibody showing the deposits of C3 (C) and absence of C9 (D). Original magnification, × 250. Details of image acquisition are given in Dobrina et al.²³