SPIO-mediated complement activation in knockout mouse sera. (a) Model of worm-like polycrystalline SPIO NW shows magnetite/maghemite crystals (10 nm, brown color) randomly coated with 20 kDa dextran chains (arrow). Size bar for transmission electron microscopy image: 100 nm; (b) scheme of C3 chains and cleaved fragments; (c) nanoparticles were incubated with normal mouse sera (C57BL/6) and C3 fragments were detected on purified SPIO NW or in whole serum by western blotting. Fragments of C3 are clearly detected in purified SPIO NW sample. Zymosan particles (1 mg/ml) also showed strong complement activation; (d) deposition of C3 fragments on SPIO NW surface as a function of normal serum concentration as detected with dot blot immunoassay (see Methods); (e) deposition of C3 fragments in sera deficient for the LP components shows complete dependency on the MBL-MASP-2 but not on FcnA. All experiments were repeated at least three times based on n = 3; (f) deposition of C3 fragments in normal mouse sera pre-incubated with different concentrations of the LP inhibitor mannose; (g) deposition of C3 fragments in sera deficient for the AP. N = 3 for each bar, repeated at least 3 times. ***p < 0.0001, and **p < 0.01.