Biological functions of Mycobacterium tuberculosis-specific CD4+T cells were impaired by tuberculosis pleural fluid

► Pleural fluid inhibits Mycobacterium tuberculosis-specific Th1 cytokines production. ► Cell activation and division are vigorously impaired. ► Timing of interaction with pleural fluid has an impact on cell functions. Immunosuppressive factors in pleural fluid contribute to the suppressive effect.