Antibody-Dependent Cell-Mediated Phagocytosis of Influenza Virus

Isolation of human neutrophils from peripheral blood was carried out by using Ficoll-Paque PLUS density gradient (GE Healthcare) according to the procedures described previously [51 (link)]. ADCP by THP1 cells (from ATCC) and neutrophils was performed essentially as a previous report [52 (link)]. Control IgG was purchased from GeneTex (GTX16193). Briefly, Cal/09 virus was incubated with indicated antibodies at 37°C for 1 h and added to the sialidase (0.5 unit/mL, Sigma) pre-treated THP-1 cells or neutrophils. After 1 h incubation, THP-1 cells or neutrophils were washed three times with RPMI and incubated at 37°C. After 6 h incubation, THP-1 cells or neutrophils were fixed in 4% paraformaldehyde, permeabilized and stained with anti-influenza NP antibody (Abcam, Ab20921, 1:100 dilution). The levels of phagocytosis were monitored by flow cytometry.