SETTING We recently showed that treatment failure rate was higher among multidrug-resistant tuberculosis (MDR-TB) patients without a previous history of tuberculosis (TB) treatment, or so-called 'primary resistance'.

OBJECTIVE To investigate the phosphorylation levels of signal transducers and activators of transcription-1 (STAT-1) and STAT-4 and the subsequent cytokine release as a possible cause of a poor prognosis in MDR-TB patients with primary resistance.

DESIGN Ten patients with successfully treated pulmonary TB without resistance, 12 MDR-TB patients with acquired resistance and 10 MDR-TB patients with primary resistance were enrolled. After 24 h stimulation of peripheral blood mononuclear cells (PBMC) with interferon-gamma (IFN-gamma), interleukin-12 (IL-12), purified protein derivative (PPD), or lysate of Mycobacterium tuberculosis, flow cytometric analysis of intracellular pSTAT-1 and pSTAT-4 were performed and secretion of IFN-gamma, IL-12p40 and tumour necrosis factor-alpha (TNF-alpha) was measured in culture supernatant.

RESULTS The mean fluorescent intensities of pSTAT-1 and pSTAT-4 in PBMC of MDR-TB patients with primary resistance decreased on stimulation of IFN-gamma, PPD or lysate of M. tuberculosis when compared with patients with acquired resistance. In addition, secretion of IFN-gamma, IL-12p40 and TNF-alpha in these patients decreased on various stimuli.

CONCLUSION Decreased phosphorylation of STAT-1, STAT-4, and of subsequent cytokine release, might be associated with a poor prognosis in MDR-TB patients with primary resistance.