FOXP3 and Pleural effusion: We found statistically higher frequency of CD4+CD25+ FoxP3+ T cells in MPE with malignant cells (I) than in nonmalignant pleural effusions (III) (3.29% ± 2.99% versus 0.82% ± 0.66%, p = 0.000009) and in MPE without malignant cells (II) compared to nonmalignant pleural effusions (III) (2.46% ± 2.53% versus 0.82% ± 0.66%, p = 0.0015).