Role of soluble interleukin-2 receptor levels in patients with latent tuberculosis.

Serum soluble interleukin-2 receptor (sIL-2R) serves as a marker of disease activity in patients with tuberculosis (TB). However, little is known about its role in latent TB. The aim of this study was to assess the levels of sIL-2R in patients with latent TB and correlate them with the purified protein derivate (PPD) test results. Patients with a diagnosis of latent TB were divided into three subgroups by induration size: <10 mm, 10-20 mm, >20 mm. Blood was collected for sIL-2R assay. Findings were compared to a healthy control group. The study group consisted of 44 patients (68% male) of mean ( +/- SD) age 20 +/- 10 years, and the control group consisted of 41 subjects (42% male) aged 31 +/- 11 years. Comparison of the two groups yielded a significantly higher serum sIL-2R level in the patients (450 +/- 224 U/ml vs. 374 +/- 30 U/ml, p = 0.03). Mean sIL-2R levels were significantly correlated with the presence of latent TB (p = 0.03), and with purified protein derivative (PPD) subgroups: 387 +/- 177 U/ml for induration size <10 mm, NS; 450 +/- 238 U/ml for 10-20 mm, p = 0.04, and 605 +/- 235 U/ml for >20 mm, p < 0.0001. sIL-2R assay may serve as an additional tool to estimate the extent of the immune response in patients with latent TB.