The BAL liquid should be filtered through a stainless steal sieve with a pore size of 0,2mm into a 50mL polystyrol centrifugation tube (e.g. Nunc). As alternative sterile disposable nylon sieves or sterile gauze can be used. These alternative materials have to be validated before use to ensure there is no loss of cells compared to using the sieve. The disposable BD FaIconT"' 100pm Cell Strainer (cat nos 352360) has been used successfully.