Regulatory T cells (T_reg) increase in active tuberculosis (TB). However, whether T_reg-mediated immune suppression affect the susceptibility to active TB or development of multidrug-resistant (MDR) TB is not yet clear. We compared circulatory T_reg frequencies in drug susceptible (DS) and MDR TB before and after anti-TB treatment.

Circulatory T_reg frequencies were measured in blood samples from 33 DS TB, 7 mycobacterial culture-positive active MDR TB, 16 stable MDR TB who had been culture negative for at least 6 months, and 14 healthy controls before and after treatment. T_reg frequency was measured by flow cytometry using cell-surface marker CD4 and intracellular marker FoxP3.

T_reg frequency was higher in DS TB and active MDR TB patients than in healthy controls (p < 0.05), with no significant difference between the former. T_reg frequency was higher in patients with sputum acid-fast bacilli smear-positive TB than in patients with smear-negative TB, but the increase did not correlate with the radiologic extent of TB or presence of a cavity. After successful treatment, T_reg decreased to control levels in DS TB and MDR TB patents.

The pattern of change, in which T_reg frequency increased during active infection and normalized to control levels after successful treatment, was similar in DS and MDR TB patients.