Immune response profile in patients with active tuberculosis in a BCG vaccinated area

Tuberculosis patients with pulmonary (N = 95) or lymph node disease (N = 23) were assessed for Th1 responses (PPD skin test and lymphocyte blastogenic and interferon gamma) and Th2 responses (polyclonal and antigen specific IgE). Skin test responses to PPD and lymphocyte proliferative responses to crude mycobacterial antigens (PPD, culture filtrate and sonicate) and recall antigens (tetanus toxoid and streptolysin O) were significantly suppressed (p < 0.001) in patients with pulmonary disease compared to endemic controls. However, mitogen (phytohemagglutinin)-stimulated responses were comparable in patients and controls. Polyclonal and antigen specific (M. tuberculosis culture filtrate) IgE responses which are considered to be surrogate markers for Th2 responses were significantly higher in patients with pulmonary disease compared to healthy endemic controls (Mann Whitney analysis p < 0.01). Patients with lymph node disease showed strong Th1 responses but did not show significant responses for either polyclonal or antigen specific IgE. Thus overall suppression of T cell memory response was observed only in patients with pulmonary disease but not in patients with lymph node disease suggesting that sequestration of antigen in different compartments leads to differential activation of Th1 and Th2 responses. PPD skin test responses were highly positive in endemic controls (47% positive) and household contacts (86% positive). Furthermore, PPD positivity decreased with disease severity. Therefore PPD positivity in a BCG vaccinated TB endemic area cannot be used as a diagnostic marker for active tuberculosis particularly in advanced disease.