ALB and Pleural effusion: After depletion of six abundant proteins (albumin, immunoglobulin G, immunoglobulin A, transferrin, α1-antitrypsin, and haptoglobin) using affinity column, the pleural effusion samples from 4 UPPE patients and 4 CPPE patients were pooled equally (10 μg proteins from each patient) into the UPPE group and the CPPE group (Exp 1), respectively, to diminish the influences of between-individual variations.