High level of interferon gamma in tuberculous pleural effusion

It has been observed that T-lymphocytes of patients with tuberculosis produce interferon gamma (IFNγ) in vitro. Based on this idea, we studied IFNγ in pleural fluid and serum. We studied 80 patients with pleural effusion; 30 patients with tuberculous pleurisy had high IFNγ concentrations in pleural fluid. Patients with malignant pleural effusions, nonspecific pleural effusion, parapneumonic effusions and pleural transudates had low levels. The IFNγ levels were higher in those with massive tuberculous effusion and apparent pulmonary lesion on x-ray film. We found that the T4/T8 lymphocyte ratio was higher in pleural fluid than in peripheral blood. Numbers of T3 and T4 lymphocytes were higher in tuberculous pleural effusions compared with those in other patients. There is no correlation between IFNγ levels and lymphocyte subsets in pleural effusion. Perhaps pleural T-lymphocytes produce IFNγ after stimulation by mycobacterial antigens and this lymphokine activates macrophages, increasing their bactericidal activity against Mycobacterium tuberculosis.