We all want a good test for tuberculosis. Sputum smears are negative in half of those with lung involvement.1 How can we detect tuberculosis if there are <105 bacilli per ml of sputum? We could use either a more sensitive test for something the tubercle bacillus produces or use the host’s response to amplify the signal. Mycobacterial culture, DNA-based amplification,2 breath tests for volatile organic chemicals3 and lipid profiles4 5 exhibit the first approach. Chest radiographs, non-specific inflammatory markers and tests based on the specific immune response (such as tuberculin testing) exploit the second option.

Local immune responses have previously been shown to have greater potential for diagnostic assays than systemic responses from peripheral blood.6 7 Studies using cells …