A549 is a human lung adenocarcinoma cell line commonly used in biomedical research. Here is a general protocol for culturing A549 cells:

1. Prepare A549 cell culture media: RPMI-1640 media supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin solution.
2. Thaw frozen A549 cells and seed them in a T25 flask containing 5-10 mL of the prepared media.
3. Incubate the cells in a humidified incubator at 37°C with 5% CO2.
4. Monitor the cells daily and change the media every 2-3 days.
5. Once the cells reach 80-90% confluency, detach them using 0.25% trypsin-EDTA solution and centrifuge at 1000 rpm for 5 minutes.
6. Re-suspend the cells in fresh media and seed them at the desired density for experiments.

Note: The protocol may vary depending on the specific experiment being performed.