IgG from patients with SLE augments PMN recruitment via FcγRIIa. (A) HMEC-1 cell binding of SLE sera with high- and low-binding activity, as tested by ELISA. (B) Titration of IgG fractions with high- and low-AECA activity on unstimulated and TNFα-stimulated HMEC-1 cells, as tested by ELISA. Values are mean of triplicates ± standard deviation. (C) Purified IgG from sera of patients with SLE with high-level AECA activity was perfused at 400 μg/mL over HMEC-1 cells at 0.83 mL/minute for 5 minutes, after which antibody binding was determined by confocal imaging with biotinylated-conjugated anti–human IgG and AlexaFluor 488 streptavidin. Main panel shows composite Z-stacks and the lower inserts show cell cross-section. Arrows point to the deposition of human Ig on the apical surface of the cells. (D) Deposition of SLE IgG (400 μg/mL) with high-level anti-EC activity enhanced PMN adhesion at 1.5 dynes/cm² to TNFα-stimulated HMEC-1 cells (*P < .03 compared with either no AECA or IgG with low-AECA activity). Values are mean + SEM of 3 experiments. Panel E shows that AECA-stimulated PMN adhesion at 1.5 dynes/cm² was fully inhibited by anti-FcγRIIa (IV.3) but not by fab′ anti-FcγRIIIb (3G8) (*P < .02). All values are mean + SEM of 3 experiments.