Neutrophil phagocytic activity of IgA depleted plasma samples was tested on primary human neutrophils44 (link). Biotinylated antigens were coupled to fluorescent neutravidin beads (Thermo Fisher) and incubated 1:100 diluted plasma. Primary neutrophils were incubated with immune complexes for 1h at 37°C. Next, cells were stained for surface CD66b expression with a 1:100 diluted antibody (Biolegend, CA, USA; clone: G10F5), fixed with 4% paraformaldehyde, analyzed by flow cytometry, and phagocytosis score calculated as described above (Supplemental Figure 14).