Phagocytic activity of macrophages
To evaluate neutral red phagocytosis by peritoneal macrophages, 100 µl of 0.075% aseptic neutral red solution was added and incubated for 1 h. The supernatant was discarded and the cells were washed twice with PBS. Then, 100 µl of cell lysate solution (ethanol 50% and 1% acetic acid at the ratio of 1:1) was added to a 96-well plate to lyse the cells at room temperature for 2 h. The optical density at 540 nm was measured by ELISA reader.