APL-positive IgG fail to induce thrombus formation and vessel occlusions in C6-deficient rats. Six C6^+/+ PVG rats (□) and an equal number of C6^-/- PVG (▦) rats received LPS and 3 hours later aPL-positive IgG from 3 patients with APS (A, C, and D). An additional group of 6 C6^+/+ PVG rats (▪) received LPS followed by aPL-negative IgG. All rats were examined for the number of thrombi (A) and occluded vessels (B). Thrombi and vessel occlusions were significantly reduced in C6^-/- rats. These parameters were evaluated on 2 rats for each IgG sample. The results are expressed as mean ± SD. ^*P < .05, ^**P < .01 versus C6^-/- PVG receiving aPL-positive IgG; ns indicates not significant. Error bars indicate standard deviation (SD).