Human AM were cultured and infected with PR/8 at the designated MOI. Uptake of zymosan or heat-killed S. aureus were performed according to manufacturer's instructions. For uptake of zymosan, cells were incubated with fluorescent-labeled zymosan A Bioparticles (Invitrogen) at a ratio of 10 particles per cell for 2 h, then cells were washed and fixed with 4% paraformaldehyde for 10 min. The uptake was analyzed by fluorescent microscopy. For uptake of heat-killed S. aureus, cells were incubated with pHrodolabeled, heat-killed S. aureus (pHrodo-SA) (Invitrogen) at a ratio of 20 particles per cell for 2 h. The cells were then washed to remove non-internalized particles, collected, and fixed with 4% paraformaldehyde. Uptake of the pHrodo-SA was analyzed on the LSR II flow cytometer (BD Biosciences) in the National Jewish Health Flow Cytometry Core, and the data were analyzed using FlowJo software (TreeStar, Ashland, OR). In addition to the PR/8 infected cells, positive control uninfected cells and negative control paraformaldehyde fixed cells were also used.