Low fucosylation and high galactosylation of the IgG tail enhances adhesion to VWF. Platelet adhesion to slides coated with immune complexes containing recombinant SARS-CoV-2 spike protein and COVA1-18 recombinant anti-spike IgG with modified glycosylation. (Ai) Numbers of platelets adhered to glass slides coated with FCS (negative control), spike protein only, or spike protein plus unmodified IgG (WT) or IgG modified to have Low Fuc, High Gal, or Low Fuc High Gal and (Aii) representative images (acquired at ×20 original magnification) of adhered platelets stained with DiOC₆. (Bi) Numbers of platelets adhered to VWF plus immune complexes containing spike protein and modified IgGs and (Bii) representative images (acquired at ×20 original magnification) of adhered platelets. (Ci) Volume of thrombi formed on VWF with immune complexes containing spike and either WT IgG or IgG with modified glyosylation and (Cii) representative images (acquired at ×20 original magnification) of thrombi stained with DiOC₆. (D) Volume of thrombi formed on spike, WT IgG, Low Fuc High Gal IgG, or VWF alone and in combination. Values are mean ± standard error of the mean (SEM). Significant differences were tested by 2-way analysis of variance (ANOVA) with the Tukey multiple comparisons test. *P < .05; **P < .01. n.s., not significant.