A new automated flow cytometric method for BALF leukocyte differentiation, using four antibodies (anti-CD45, anti-CD66b, anti-HLA-DR, anti-CD52) given to human BALF in one tube, was developed and prospectively validated in 745 unselected subsequent BALF samples from patients with interstitial lung diseases (455 patients), infectious diseases (196 patients), and other diseases (94 patients). This evidence concerns the gene PTPRC and interstitial lung disease.