Physical interactions of HIT ULICs and C1q. (A) C1q increases the size of HIT ULICs. PF4 (10 µg/mL) and heparin (H; 0.1 U/mL) were incubated alone or with KKO (50 µg/mL) to generate ULICs. C1q was added to KKO ULICs at molar ratio of 1:4, and size of the complexes was measured by dynamic light scattering. The mean ± standard error of the mean of 3 independent experiments is shown. P < .001 for PF4/heparin + KKO + C1q vs all other conditions starting at 1 hour (2-way analysis of variance). (B) C1q restores formation of ULICs. PF4 (10 µg/mL), KKO (30 µg/mL), RTO (350 µg/mL), and heparin (0.2 U/mL) were preincubated, and buffer alone or buffer containing C1q (1:16 ratio with KKO) was added 1 hour later. The percentage of small particles (<20 nm) is shown at the indicated times. The mean ± standard error of the mean of 3 experiments is shown.